xact.c

/*-------------------------------------------------------------------------
 *
 * xact.c
 *	  top level transaction system support routines
 *
 * See src/backend/access/transam/README for more information.
 *
 * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.241 2007/04/30 03:23:48 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <time.h>
#include <unistd.h>

#include "access/multixact.h"
#include "access/subtrans.h"
#include "access/transam.h"
#include "access/twophase.h"
#include "access/xact.h"
#include "access/xlogutils.h"
#include "catalog/namespace.h"
#include "commands/async.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "libpq/be-fsstubs.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/fd.h"
#include "storage/lmgr.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/combocid.h"
#include "utils/flatfiles.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/relcache.h"


/*
 *	User-tweakable parameters
 */
int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
int			XactIsoLevel;

bool		DefaultXactReadOnly = false;
bool		XactReadOnly;

int			CommitDelay = 0;	/* precommit delay in microseconds */
int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */


/*
 *	transaction states - transaction state from server perspective
 */
typedef enum TransState
{
	TRANS_DEFAULT,
	TRANS_START,
	TRANS_INPROGRESS,
	TRANS_COMMIT,
	TRANS_ABORT,
	TRANS_PREPARE
} TransState;

/*
 *	transaction block states - transaction state of client queries
 *
 * Note: the subtransaction states are used only for non-topmost
 * transactions; the others appear only in the topmost transaction.
 */
typedef enum TBlockState
{
	/* not-in-transaction-block states */
	TBLOCK_DEFAULT,				/* idle */
	TBLOCK_STARTED,				/* running single-query transaction */

	/* transaction block states */
	TBLOCK_BEGIN,				/* starting transaction block */
	TBLOCK_INPROGRESS,			/* live transaction */
	TBLOCK_END,					/* COMMIT received */
	TBLOCK_ABORT,				/* failed xact, awaiting ROLLBACK */
	TBLOCK_ABORT_END,			/* failed xact, ROLLBACK received */
	TBLOCK_ABORT_PENDING,		/* live xact, ROLLBACK received */
	TBLOCK_PREPARE,				/* live xact, PREPARE received */

	/* subtransaction states */
	TBLOCK_SUBBEGIN,			/* starting a subtransaction */
	TBLOCK_SUBINPROGRESS,		/* live subtransaction */
	TBLOCK_SUBEND,				/* RELEASE received */
	TBLOCK_SUBABORT,			/* failed subxact, awaiting ROLLBACK */
	TBLOCK_SUBABORT_END,		/* failed subxact, ROLLBACK received */
	TBLOCK_SUBABORT_PENDING,	/* live subxact, ROLLBACK received */
	TBLOCK_SUBRESTART,			/* live subxact, ROLLBACK TO received */
	TBLOCK_SUBABORT_RESTART		/* failed subxact, ROLLBACK TO received */
} TBlockState;

/*
 *	transaction state structure
 */
typedef struct TransactionStateData
{
	TransactionId transactionId;	/* my XID, or Invalid if none */
	SubTransactionId subTransactionId;	/* my subxact ID */
	char	   *name;			/* savepoint name, if any */
	int			savepointLevel; /* savepoint level */
	TransState	state;			/* low-level state */
	TBlockState blockState;		/* high-level state */
	int			nestingLevel;	/* nest depth */
	MemoryContext curTransactionContext;		/* my xact-lifetime context */
	ResourceOwner curTransactionOwner;	/* my query resources */
	List	   *childXids;		/* subcommitted child XIDs */
	Oid			currentUser;	/* subxact start current_user */
	bool		prevXactReadOnly;		/* entry-time xact r/o state */
	struct TransactionStateData *parent;		/* back link to parent */
} TransactionStateData;

typedef TransactionStateData *TransactionState;

/*
 * CurrentTransactionState always points to the current transaction state
 * block.  It will point to TopTransactionStateData when not in a
 * transaction at all, or when in a top-level transaction.
 */
static TransactionStateData TopTransactionStateData = {
	0,							/* transaction id */
	0,							/* subtransaction id */
	NULL,						/* savepoint name */
	0,							/* savepoint level */
	TRANS_DEFAULT,				/* transaction state */
	TBLOCK_DEFAULT,				/* transaction block state from the client
								 * perspective */
	0,							/* nesting level */
	NULL,						/* cur transaction context */
	NULL,						/* cur transaction resource owner */
	NIL,						/* subcommitted child Xids */
	0,							/* entry-time current userid */
	false,						/* entry-time xact r/o state */
	NULL						/* link to parent state block */
};

static TransactionState CurrentTransactionState = &TopTransactionStateData;

/*
 * The subtransaction ID and command ID assignment counters are global
 * to a whole transaction, so we do not keep them in the state stack.
 */
static SubTransactionId currentSubTransactionId;
static CommandId currentCommandId;

/*
 * xactStartTimestamp is the value of transaction_timestamp().
 * stmtStartTimestamp is the value of statement_timestamp().
 * xactStopTimestamp is the time at which we log a commit or abort WAL record.
 * These do not change as we enter and exit subtransactions, so we don't
 * keep them inside the TransactionState stack.
 */
static TimestampTz xactStartTimestamp;
static TimestampTz stmtStartTimestamp;
static TimestampTz xactStopTimestamp;

/*
 * GID to be used for preparing the current transaction.  This is also
 * global to a whole transaction, so we don't keep it in the state stack.
 */
static char *prepareGID;

/*
 * Private context for transaction-abort work --- we reserve space for this
 * at startup to ensure that AbortTransaction and AbortSubTransaction can work
 * when we've run out of memory.
 */
static MemoryContext TransactionAbortContext = NULL;

/*
 * List of add-on start- and end-of-xact callbacks
 */
typedef struct XactCallbackItem
{
	struct XactCallbackItem *next;
	XactCallback callback;
	void	   *arg;
} XactCallbackItem;

static XactCallbackItem *Xact_callbacks = NULL;

/*
 * List of add-on start- and end-of-subxact callbacks
 */
typedef struct SubXactCallbackItem
{
	struct SubXactCallbackItem *next;
	SubXactCallback callback;
	void	   *arg;
} SubXactCallbackItem;

static SubXactCallbackItem *SubXact_callbacks = NULL;


/* local function prototypes */
static void AssignSubTransactionId(TransactionState s);
static void AbortTransaction(void);
static void AtAbort_Memory(void);
static void AtCleanup_Memory(void);
static void AtAbort_ResourceOwner(void);
static void AtCommit_LocalCache(void);
static void AtCommit_Memory(void);
static void AtStart_Cache(void);
static void AtStart_Memory(void);
static void AtStart_ResourceOwner(void);
static void CallXactCallbacks(XactEvent event);
static void CallSubXactCallbacks(SubXactEvent event,
					 SubTransactionId mySubid,
					 SubTransactionId parentSubid);
static void CleanupTransaction(void);
static void CommitTransaction(void);
static void RecordTransactionAbort(void);
static void StartTransaction(void);

static void RecordSubTransactionCommit(void);
static void StartSubTransaction(void);
static void CommitSubTransaction(void);
static void AbortSubTransaction(void);
static void CleanupSubTransaction(void);
static void PushTransaction(void);
static void PopTransaction(void);

static void AtSubAbort_Memory(void);
static void AtSubCleanup_Memory(void);
static void AtSubAbort_ResourceOwner(void);
static void AtSubCommit_Memory(void);
static void AtSubStart_Memory(void);
static void AtSubStart_ResourceOwner(void);

static void ShowTransactionState(const char *str);
static void ShowTransactionStateRec(TransactionState state);
static const char *BlockStateAsString(TBlockState blockState);
static const char *TransStateAsString(TransState state);


/* ----------------------------------------------------------------
 *	transaction state accessors
 * ----------------------------------------------------------------
 */

/*
 *	IsTransactionState
 *
 *	This returns true if we are currently running a query
 *	within an executing transaction.
 */
bool
IsTransactionState(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->state)
	{
		case TRANS_DEFAULT:
			return false;
		case TRANS_START:
			return true;
		case TRANS_INPROGRESS:
			return true;
		case TRANS_COMMIT:
			return true;
		case TRANS_ABORT:
			return true;
		case TRANS_PREPARE:
			return true;
	}

	/*
	 * Shouldn't get here, but lint is not happy without this...
	 */
	return false;
}

/*
 *	IsAbortedTransactionBlockState
 *
 *	This returns true if we are currently running a query
 *	within an aborted transaction block.
 */
bool
IsAbortedTransactionBlockState(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->blockState == TBLOCK_ABORT ||
		s->blockState == TBLOCK_SUBABORT)
		return true;

	return false;
}


/*
 *	GetTopTransactionId
 *
 * Get the ID of the main transaction, even if we are currently inside
 * a subtransaction.
 */
TransactionId
GetTopTransactionId(void)
{
	return TopTransactionStateData.transactionId;
}


/*
 *	GetCurrentTransactionId
 *
 * We do not assign XIDs to subtransactions until/unless this is called.
 * When we do assign an XID to a subtransaction, recursively make sure
 * its parent has one as well (this maintains the invariant that a child
 * transaction has an XID following its parent's).
 */
TransactionId
GetCurrentTransactionId(void)
{
	TransactionState s = CurrentTransactionState;

	if (!TransactionIdIsValid(s->transactionId))
		AssignSubTransactionId(s);

	return s->transactionId;
}

static void
AssignSubTransactionId(TransactionState s)
{
	ResourceOwner currentOwner;

	Assert(s->parent != NULL);
	Assert(s->state == TRANS_INPROGRESS);
	if (!TransactionIdIsValid(s->parent->transactionId))
		AssignSubTransactionId(s->parent);

	/*
	 * Generate a new Xid and record it in PG_PROC and pg_subtrans.
	 *
	 * NB: we must make the subtrans entry BEFORE the Xid appears anywhere in
	 * shared storage other than PG_PROC; because if there's no room for it in
	 * PG_PROC, the subtrans entry is needed to ensure that other backends see
	 * the Xid as "running".  See GetNewTransactionId.
	 */
	s->transactionId = GetNewTransactionId(true);

	SubTransSetParent(s->transactionId, s->parent->transactionId);

	/*
	 * Acquire lock on the transaction XID.  (We assume this cannot block.) We
	 * have to be sure that the lock is assigned to the transaction's
	 * ResourceOwner.
	 */
	currentOwner = CurrentResourceOwner;
	PG_TRY();
	{
		CurrentResourceOwner = s->curTransactionOwner;

		XactLockTableInsert(s->transactionId);
	}
	PG_CATCH();
	{
		/* Ensure CurrentResourceOwner is restored on error */
		CurrentResourceOwner = currentOwner;
		PG_RE_THROW();
	}
	PG_END_TRY();
	CurrentResourceOwner = currentOwner;
}


/*
 *	GetCurrentTransactionIdIfAny
 *
 * Unlike GetCurrentTransactionId, this will return InvalidTransactionId
 * if we are currently not in a transaction, or in a transaction or
 * subtransaction that has not yet assigned itself an XID.
 */
TransactionId
GetCurrentTransactionIdIfAny(void)
{
	TransactionState s = CurrentTransactionState;

	return s->transactionId;
}


/*
 *	GetCurrentSubTransactionId
 */
SubTransactionId
GetCurrentSubTransactionId(void)
{
	TransactionState s = CurrentTransactionState;

	return s->subTransactionId;
}


/*
 *	GetCurrentCommandId
 */
CommandId
GetCurrentCommandId(void)
{
	/* this is global to a transaction, not subtransaction-local */
	return currentCommandId;
}

/*
 *	GetCurrentTransactionStartTimestamp
 */
TimestampTz
GetCurrentTransactionStartTimestamp(void)
{
	return xactStartTimestamp;
}

/*
 *	GetCurrentStatementStartTimestamp
 */
TimestampTz
GetCurrentStatementStartTimestamp(void)
{
	return stmtStartTimestamp;
}

/*
 *	GetCurrentTransactionStopTimestamp
 *
 * We return current time if the transaction stop time hasn't been set
 * (which can happen if we decide we don't need to log an XLOG record).
 */
TimestampTz
GetCurrentTransactionStopTimestamp(void)
{
	if (xactStopTimestamp != 0)
		return xactStopTimestamp;
	return GetCurrentTimestamp();
}

/*
 *	SetCurrentStatementStartTimestamp
 */
void
SetCurrentStatementStartTimestamp(void)
{
	stmtStartTimestamp = GetCurrentTimestamp();
}

/*
 *	SetCurrentTransactionStopTimestamp
 */
static inline void
SetCurrentTransactionStopTimestamp(void)
{
	xactStopTimestamp = GetCurrentTimestamp();
}

/*
 *	GetCurrentTransactionNestLevel
 *
 * Note: this will return zero when not inside any transaction, one when
 * inside a top-level transaction, etc.
 */
int
GetCurrentTransactionNestLevel(void)
{
	TransactionState s = CurrentTransactionState;

	return s->nestingLevel;
}


/*
 *	TransactionIdIsCurrentTransactionId
 */
bool
TransactionIdIsCurrentTransactionId(TransactionId xid)
{
	TransactionState s;

	/*
	 * We always say that BootstrapTransactionId is "not my transaction ID"
	 * even when it is (ie, during bootstrap).	Along with the fact that
	 * transam.c always treats BootstrapTransactionId as already committed,
	 * this causes the tqual.c routines to see all tuples as committed, which
	 * is what we need during bootstrap.  (Bootstrap mode only inserts tuples,
	 * it never updates or deletes them, so all tuples can be presumed good
	 * immediately.)
	 *
	 * Likewise, InvalidTransactionId and FrozenTransactionId are certainly
	 * not my transaction ID, so we can just return "false" immediately for
	 * any non-normal XID.
	 */
	if (!TransactionIdIsNormal(xid))
		return false;

	/*
	 * We will return true for the Xid of the current subtransaction, any of
	 * its subcommitted children, any of its parents, or any of their
	 * previously subcommitted children.  However, a transaction being aborted
	 * is no longer "current", even though it may still have an entry on the
	 * state stack.
	 */
	for (s = CurrentTransactionState; s != NULL; s = s->parent)
	{
		ListCell   *cell;

		if (s->state == TRANS_ABORT)
			continue;
		if (!TransactionIdIsValid(s->transactionId))
			continue;			/* it can't have any child XIDs either */
		if (TransactionIdEquals(xid, s->transactionId))
			return true;
		foreach(cell, s->childXids)
		{
			if (TransactionIdEquals(xid, lfirst_xid(cell)))
				return true;
		}
	}

	return false;
}


/*
 *	CommandCounterIncrement
 */
void
CommandCounterIncrement(void)
{
	currentCommandId += 1;
	if (currentCommandId == FirstCommandId)		/* check for overflow */
	{
		currentCommandId -= 1;
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
		  errmsg("cannot have more than 2^32-1 commands in a transaction")));
	}

	/* Propagate new command ID into static snapshots, if set */
	if (SerializableSnapshot)
		SerializableSnapshot->curcid = currentCommandId;
	if (LatestSnapshot)
		LatestSnapshot->curcid = currentCommandId;

	/*
	 * make cache changes visible to me.
	 */
	AtCommit_LocalCache();
	AtStart_Cache();
}


/* ----------------------------------------------------------------
 *						StartTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	AtStart_Cache
 */
static void
AtStart_Cache(void)
{
	AcceptInvalidationMessages();
}

/*
 *	AtStart_Memory
 */
static void
AtStart_Memory(void)
{
	TransactionState s = CurrentTransactionState;

	/*
	 * If this is the first time through, create a private context for
	 * AbortTransaction to work in.  By reserving some space now, we can
	 * insulate AbortTransaction from out-of-memory scenarios.  Like
	 * ErrorContext, we set it up with slow growth rate and a nonzero
	 * minimum size, so that space will be reserved immediately.
	 */
	if (TransactionAbortContext == NULL)
		TransactionAbortContext =
			AllocSetContextCreate(TopMemoryContext,
								  "TransactionAbortContext",
								  32 * 1024,
								  32 * 1024,
								  32 * 1024);

	/*
	 * We shouldn't have a transaction context already.
	 */
	Assert(TopTransactionContext == NULL);

	/*
	 * Create a toplevel context for the transaction.
	 */
	TopTransactionContext =
		AllocSetContextCreate(TopMemoryContext,
							  "TopTransactionContext",
							  ALLOCSET_DEFAULT_MINSIZE,
							  ALLOCSET_DEFAULT_INITSIZE,
							  ALLOCSET_DEFAULT_MAXSIZE);

	/*
	 * In a top-level transaction, CurTransactionContext is the same as
	 * TopTransactionContext.
	 */
	CurTransactionContext = TopTransactionContext;
	s->curTransactionContext = CurTransactionContext;

	/* Make the CurTransactionContext active. */
	MemoryContextSwitchTo(CurTransactionContext);
}

/*
 *	AtStart_ResourceOwner
 */
static void
AtStart_ResourceOwner(void)
{
	TransactionState s = CurrentTransactionState;

	/*
	 * We shouldn't have a transaction resource owner already.
	 */
	Assert(TopTransactionResourceOwner == NULL);

	/*
	 * Create a toplevel resource owner for the transaction.
	 */
	s->curTransactionOwner = ResourceOwnerCreate(NULL, "TopTransaction");

	TopTransactionResourceOwner = s->curTransactionOwner;
	CurTransactionResourceOwner = s->curTransactionOwner;
	CurrentResourceOwner = s->curTransactionOwner;
}

/* ----------------------------------------------------------------
 *						StartSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubStart_Memory
 */
static void
AtSubStart_Memory(void)
{
	TransactionState s = CurrentTransactionState;

	Assert(CurTransactionContext != NULL);

	/*
	 * Create a CurTransactionContext, which will be used to hold data that
	 * survives subtransaction commit but disappears on subtransaction abort.
	 * We make it a child of the immediate parent's CurTransactionContext.
	 */
	CurTransactionContext = AllocSetContextCreate(CurTransactionContext,
												  "CurTransactionContext",
												  ALLOCSET_DEFAULT_MINSIZE,
												  ALLOCSET_DEFAULT_INITSIZE,
												  ALLOCSET_DEFAULT_MAXSIZE);
	s->curTransactionContext = CurTransactionContext;

	/* Make the CurTransactionContext active. */
	MemoryContextSwitchTo(CurTransactionContext);
}

/*
 * AtSubStart_ResourceOwner
 */
static void
AtSubStart_ResourceOwner(void)
{
	TransactionState s = CurrentTransactionState;

	Assert(s->parent != NULL);

	/*
	 * Create a resource owner for the subtransaction.	We make it a child of
	 * the immediate parent's resource owner.
	 */
	s->curTransactionOwner =
		ResourceOwnerCreate(s->parent->curTransactionOwner,
							"SubTransaction");

	CurTransactionResourceOwner = s->curTransactionOwner;
	CurrentResourceOwner = s->curTransactionOwner;
}

/* ----------------------------------------------------------------
 *						CommitTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	RecordTransactionCommit
 */
void
RecordTransactionCommit(void)
{
	int			nrels;
	RelFileNode *rels;
	int			nchildren;
	TransactionId *children;

	/* Get data needed for commit record */
	nrels = smgrGetPendingDeletes(true, &rels);
	nchildren = xactGetCommittedChildren(&children);

	/*
	 * If we made neither any XLOG entries nor any temp-rel updates, and have
	 * no files to be deleted, we can omit recording the transaction commit at
	 * all.  (This test includes the effects of subtransactions, so the
	 * presence of committed subxacts need not alone force a write.)
	 */
	if (MyXactMadeXLogEntry || MyXactMadeTempRelUpdate || nrels > 0)
	{
		TransactionId xid = GetCurrentTransactionId();
		bool		madeTCentries;
		XLogRecPtr	recptr;

		/* Tell bufmgr and smgr to prepare for commit */
		BufmgrCommit();

		START_CRIT_SECTION();

		/*
		 * We only need to log the commit in XLOG if the transaction made any
		 * transaction-controlled XLOG entries or will delete files.
		 */
		madeTCentries = (MyLastRecPtr.xrecoff != 0);
		if (madeTCentries || nrels > 0)
		{
			XLogRecData rdata[3];
			int			lastrdata = 0;
			xl_xact_commit xlrec;

			/*
			 * Mark ourselves as within our "commit critical section".  This
			 * forces any concurrent checkpoint to wait until we've updated
			 * pg_clog.  Without this, it is possible for the checkpoint to
			 * set REDO after the XLOG record but fail to flush the pg_clog
			 * update to disk, leading to loss of the transaction commit if
			 * the system crashes a little later.
			 *
			 * Note: we could, but don't bother to, set this flag in
			 * RecordTransactionAbort.  That's because loss of a transaction
			 * abort is noncritical; the presumption would be that it aborted,
			 * anyway.
			 *
			 * It's safe to change the inCommit flag of our own backend
			 * without holding the ProcArrayLock, since we're the only one
			 * modifying it.  This makes checkpoint's determination of which
			 * xacts are inCommit a bit fuzzy, but it doesn't matter.
			 */
			MyProc->inCommit = true;

			SetCurrentTransactionStopTimestamp();
			xlrec.xtime = timestamptz_to_time_t(xactStopTimestamp);
			xlrec.nrels = nrels;
			xlrec.nsubxacts = nchildren;
			rdata[0].data = (char *) (&xlrec);
			rdata[0].len = MinSizeOfXactCommit;
			rdata[0].buffer = InvalidBuffer;
			/* dump rels to delete */
			if (nrels > 0)
			{
				rdata[0].next = &(rdata[1]);
				rdata[1].data = (char *) rels;
				rdata[1].len = nrels * sizeof(RelFileNode);
				rdata[1].buffer = InvalidBuffer;
				lastrdata = 1;
			}
			/* dump committed child Xids */
			if (nchildren > 0)
			{
				rdata[lastrdata].next = &(rdata[2]);
				rdata[2].data = (char *) children;
				rdata[2].len = nchildren * sizeof(TransactionId);
				rdata[2].buffer = InvalidBuffer;
				lastrdata = 2;
			}
			rdata[lastrdata].next = NULL;

			recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, rdata);
		}
		else
		{
			/* Just flush through last record written by me */
			recptr = ProcLastRecEnd;
		}

		/*
		 * We must flush our XLOG entries to disk if we made any XLOG entries,
		 * whether in or out of transaction control.  For example, if we
		 * reported a nextval() result to the client, this ensures that any
		 * XLOG record generated by nextval will hit the disk before we report
		 * the transaction committed.
		 *
		 * Note: if we generated a commit record above, MyXactMadeXLogEntry
		 * will certainly be set now.
		 */
		if (MyXactMadeXLogEntry)
		{
			/*
			 * Sleep before flush! So we can flush more than one commit
			 * records per single fsync.  (The idea is some other backend may
			 * do the XLogFlush while we're sleeping.  This needs work still,
			 * because on most Unixen, the minimum select() delay is 10msec or
			 * more, which is way too long.)
			 *
			 * We do not sleep if enableFsync is not turned on, nor if there
			 * are fewer than CommitSiblings other backends with active
			 * transactions.
			 */
			if (CommitDelay > 0 && enableFsync &&
				CountActiveBackends() >= CommitSiblings)
				pg_usleep(CommitDelay);

			XLogFlush(recptr);
		}

		/*
		 * We must mark the transaction committed in clog if its XID appears
		 * either in permanent rels or in local temporary rels. We test this
		 * by seeing if we made transaction-controlled entries *OR* local-rel
		 * tuple updates.  Note that if we made only the latter, we have not
		 * emitted an XLOG record for our commit, and so in the event of a
		 * crash the clog update might be lost.  This is okay because no one
		 * else will ever care whether we committed.
		 */
		if (madeTCentries || MyXactMadeTempRelUpdate)
		{
			TransactionIdCommit(xid);
			/* to avoid race conditions, the parent must commit first */
			TransactionIdCommitTree(nchildren, children);
		}

		/* Checkpoint can proceed now */
		MyProc->inCommit = false;

		END_CRIT_SECTION();
	}

	/* Break the chain of back-links in the XLOG records I output */
	MyLastRecPtr.xrecoff = 0;
	MyXactMadeXLogEntry = false;
	MyXactMadeTempRelUpdate = false;

	/* And clean up local data */
	if (rels)
		pfree(rels);
	if (children)
		pfree(children);
}


/*
 *	AtCommit_LocalCache
 */
static void
AtCommit_LocalCache(void)
{
	/*
	 * Make catalog changes visible to me for the next command.
	 */
	CommandEndInvalidationMessages();
}

/*
 *	AtCommit_Memory
 */
static void
AtCommit_Memory(void)
{
	/*
	 * Now that we're "out" of a transaction, have the system allocate things
	 * in the top memory context instead of per-transaction contexts.
	 */
	MemoryContextSwitchTo(TopMemoryContext);

	/*
	 * Release all transaction-local memory.
	 */
	Assert(TopTransactionContext != NULL);
	MemoryContextDelete(TopTransactionContext);
	TopTransactionContext = NULL;
	CurTransactionContext = NULL;
	CurrentTransactionState->curTransactionContext = NULL;
}

/* ----------------------------------------------------------------
 *						CommitSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubCommit_Memory
 */
static void
AtSubCommit_Memory(void)
{
	TransactionState s = CurrentTransactionState;

	Assert(s->parent != NULL);

	/* Return to parent transaction level's memory context. */
	CurTransactionContext = s->parent->curTransactionContext;
	MemoryContextSwitchTo(CurTransactionContext);

	/*
	 * Ordinarily we cannot throw away the child's CurTransactionContext,
	 * since the data it contains will be needed at upper commit.  However, if
	 * there isn't actually anything in it, we can throw it away.  This avoids
	 * a small memory leak in the common case of "trivial" subxacts.
	 */
	if (MemoryContextIsEmpty(s->curTransactionContext))
	{
		MemoryContextDelete(s->curTransactionContext);
		s->curTransactionContext = NULL;
	}
}

/*
 * AtSubCommit_childXids
 *
 * Pass my own XID and my child XIDs up to my parent as committed children.
 */
static void
AtSubCommit_childXids(void)
{
	TransactionState s = CurrentTransactionState;
	MemoryContext old_cxt;

	Assert(s->parent != NULL);

	/*
	 * We keep the child-XID lists in TopTransactionContext; this avoids
	 * setting up child-transaction contexts for what might be just a few
	 * bytes of grandchild XIDs.
	 */
	old_cxt = MemoryContextSwitchTo(TopTransactionContext);

	s->parent->childXids = lappend_xid(s->parent->childXids,
									   s->transactionId);

	if (s->childXids != NIL)
	{
		s->parent->childXids = list_concat(s->parent->childXids,
										   s->childXids);

		/*
		 * list_concat doesn't free the list header for the second list; do so
		 * here to avoid memory leakage (kluge)
		 */
		pfree(s->childXids);
		s->childXids = NIL;
	}

	MemoryContextSwitchTo(old_cxt);
}

/*
 * RecordSubTransactionCommit
 */
static void
RecordSubTransactionCommit(void)
{
	/*
	 * We do not log the subcommit in XLOG; it doesn't matter until the
	 * top-level transaction commits.
	 *
	 * We must mark the subtransaction subcommitted in clog if its XID appears
	 * either in permanent rels or in local temporary rels. We test this by
	 * seeing if we made transaction-controlled entries *OR* local-rel tuple
	 * updates.  (The test here actually covers the entire transaction tree so
	 * far, so it may mark subtransactions that don't really need it, but it's
	 * probably not worth being tenser. Note that if a prior subtransaction
	 * dirtied these variables, then RecordTransactionCommit will have to do
	 * the full pushup anyway...)
	 */
	if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate)
	{
		TransactionId xid = GetCurrentTransactionId();

		/* XXX does this really need to be a critical section? */
		START_CRIT_SECTION();

		/* Record subtransaction subcommit */
		TransactionIdSubCommit(xid);

		END_CRIT_SECTION();
	}
}

/* ----------------------------------------------------------------
 *						AbortTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	RecordTransactionAbort
 */
static void
RecordTransactionAbort(void)
{
	int			nrels;
	RelFileNode *rels;
	int			nchildren;
	TransactionId *children;

	/* Get data needed for abort record */
	nrels = smgrGetPendingDeletes(false, &rels);
	nchildren = xactGetCommittedChildren(&children);

	/*
	 * If we made neither any transaction-controlled XLOG entries nor any
	 * temp-rel updates, and are not going to delete any files, we can omit
	 * recording the transaction abort at all.	No one will ever care that it
	 * aborted.  (These tests cover our whole transaction tree.)
	 */
	if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate || nrels > 0)
	{
		TransactionId xid = GetCurrentTransactionId();

		/*
		 * Catch the scenario where we aborted partway through
		 * RecordTransactionCommit ...
		 */
		if (TransactionIdDidCommit(xid))
			elog(PANIC, "cannot abort transaction %u, it was already committed", xid);

		START_CRIT_SECTION();

		/*
		 * We only need to log the abort in XLOG if the transaction made any
		 * transaction-controlled XLOG entries or will delete files. (If it
		 * made no transaction-controlled XLOG entries, its XID appears
		 * nowhere in permanent storage, so no one else will ever care if it
		 * committed.)
		 *
		 * We do not flush XLOG to disk unless deleting files, since the
		 * default assumption after a crash would be that we aborted, anyway.
		 * For the same reason, we don't need to worry about interlocking
		 * against checkpoint start.
		 */
		if (MyLastRecPtr.xrecoff != 0 || nrels > 0)
		{
			XLogRecData rdata[3];
			int			lastrdata = 0;
			xl_xact_abort xlrec;
			XLogRecPtr	recptr;

			SetCurrentTransactionStopTimestamp();
			xlrec.xtime = timestamptz_to_time_t(xactStopTimestamp);
			xlrec.nrels = nrels;
			xlrec.nsubxacts = nchildren;
			rdata[0].data = (char *) (&xlrec);
			rdata[0].len = MinSizeOfXactAbort;
			rdata[0].buffer = InvalidBuffer;
			/* dump rels to delete */
			if (nrels > 0)
			{
				rdata[0].next = &(rdata[1]);
				rdata[1].data = (char *) rels;
				rdata[1].len = nrels * sizeof(RelFileNode);
				rdata[1].buffer = InvalidBuffer;
				lastrdata = 1;
			}
			/* dump committed child Xids */
			if (nchildren > 0)
			{
				rdata[lastrdata].next = &(rdata[2]);
				rdata[2].data = (char *) children;
				rdata[2].len = nchildren * sizeof(TransactionId);
				rdata[2].buffer = InvalidBuffer;
				lastrdata = 2;
			}
			rdata[lastrdata].next = NULL;

			recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_ABORT, rdata);

			/* Must flush if we are deleting files... */
			if (nrels > 0)
				XLogFlush(recptr);
		}

		/*
		 * Mark the transaction aborted in clog.  This is not absolutely
		 * necessary but we may as well do it while we are here.
		 *
		 * The ordering here isn't critical but it seems best to mark the
		 * parent first.  This assures an atomic transition of all the
		 * subtransactions to aborted state from the point of view of
		 * concurrent TransactionIdDidAbort calls.
		 */
		TransactionIdAbort(xid);
		TransactionIdAbortTree(nchildren, children);

		END_CRIT_SECTION();
	}

	/* Break the chain of back-links in the XLOG records I output */
	MyLastRecPtr.xrecoff = 0;
	MyXactMadeXLogEntry = false;
	MyXactMadeTempRelUpdate = false;

	/* And clean up local data */
	if (rels)
		pfree(rels);
	if (children)
		pfree(children);
}

/*
 *	AtAbort_Memory
 */
static void
AtAbort_Memory(void)
{
	/*
	 * Switch into TransactionAbortContext, which should have some free
	 * space even if nothing else does.  We'll work in this context until
	 * we've finished cleaning up.
	 *
	 * It is barely possible to get here when we've not been able to create
	 * TransactionAbortContext yet; if so use TopMemoryContext.
	 */
	if (TransactionAbortContext != NULL)
		MemoryContextSwitchTo(TransactionAbortContext);
	else
		MemoryContextSwitchTo(TopMemoryContext);
}

/*
 * AtSubAbort_Memory
 */
static void
AtSubAbort_Memory(void)
{
	Assert(TransactionAbortContext != NULL);

	MemoryContextSwitchTo(TransactionAbortContext);
}


/*
 *	AtAbort_ResourceOwner
 */
static void
AtAbort_ResourceOwner(void)
{
	/*
	 * Make sure we have a valid ResourceOwner, if possible (else it will be
	 * NULL, which is OK)
	 */
	CurrentResourceOwner = TopTransactionResourceOwner;
}

/*
 * AtSubAbort_ResourceOwner
 */
static void
AtSubAbort_ResourceOwner(void)
{
	TransactionState s = CurrentTransactionState;

	/* Make sure we have a valid ResourceOwner */
	CurrentResourceOwner = s->curTransactionOwner;
}


/*
 * AtSubAbort_childXids
 */
static void
AtSubAbort_childXids(void)
{
	TransactionState s = CurrentTransactionState;

	/*
	 * We keep the child-XID lists in TopTransactionContext (see
	 * AtSubCommit_childXids).	This means we'd better free the list
	 * explicitly at abort to avoid leakage.
	 */
	list_free(s->childXids);
	s->childXids = NIL;
}

/*
 * RecordSubTransactionAbort
 */
static void
RecordSubTransactionAbort(void)
{
	int			nrels;
	RelFileNode *rels;
	TransactionId xid = GetCurrentTransactionId();
	int			nchildren;
	TransactionId *children;

	/* Get data needed for abort record */
	nrels = smgrGetPendingDeletes(false, &rels);
	nchildren = xactGetCommittedChildren(&children);

	/*
	 * If we made neither any transaction-controlled XLOG entries nor any
	 * temp-rel updates, and are not going to delete any files, we can omit
	 * recording the transaction abort at all.	No one will ever care that it
	 * aborted.  (These tests cover our whole transaction tree, and therefore
	 * may mark subxacts that don't really need it, but it's probably not
	 * worth being tenser.)
	 *
	 * In this case we needn't worry about marking subcommitted children as
	 * aborted, because they didn't mark themselves as subcommitted in the
	 * first place; see the optimization in RecordSubTransactionCommit.
	 */
	if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate || nrels > 0)
	{
		START_CRIT_SECTION();

		/*
		 * We only need to log the abort in XLOG if the transaction made any
		 * transaction-controlled XLOG entries or will delete files.
		 */
		if (MyLastRecPtr.xrecoff != 0 || nrels > 0)
		{
			XLogRecData rdata[3];
			int			lastrdata = 0;
			xl_xact_abort xlrec;
			XLogRecPtr	recptr;

			xlrec.xtime = time(NULL);
			xlrec.nrels = nrels;
			xlrec.nsubxacts = nchildren;
			rdata[0].data = (char *) (&xlrec);
			rdata[0].len = MinSizeOfXactAbort;
			rdata[0].buffer = InvalidBuffer;
			/* dump rels to delete */
			if (nrels > 0)
			{
				rdata[0].next = &(rdata[1]);
				rdata[1].data = (char *) rels;
				rdata[1].len = nrels * sizeof(RelFileNode);
				rdata[1].buffer = InvalidBuffer;
				lastrdata = 1;
			}
			/* dump committed child Xids */
			if (nchildren > 0)
			{
				rdata[lastrdata].next = &(rdata[2]);
				rdata[2].data = (char *) children;
				rdata[2].len = nchildren * sizeof(TransactionId);
				rdata[2].buffer = InvalidBuffer;
				lastrdata = 2;
			}
			rdata[lastrdata].next = NULL;

			recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_ABORT, rdata);

			/* Must flush if we are deleting files... */
			if (nrels > 0)
				XLogFlush(recptr);
		}

		/*
		 * Mark the transaction aborted in clog.  This is not absolutely
		 * necessary but XactLockTableWait makes use of it to avoid waiting
		 * for already-aborted subtransactions.
		 */
		TransactionIdAbort(xid);
		TransactionIdAbortTree(nchildren, children);

		END_CRIT_SECTION();
	}

	/*
	 * We can immediately remove failed XIDs from PGPROC's cache of running
	 * child XIDs. It's easiest to do it here while we have the child XID
	 * array at hand, even though in the main-transaction case the equivalent
	 * work happens just after return from RecordTransactionAbort.
	 */
	XidCacheRemoveRunningXids(xid, nchildren, children);

	/* And clean up local data */
	if (rels)
		pfree(rels);
	if (children)
		pfree(children);
}

/* ----------------------------------------------------------------
 *						CleanupTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	AtCleanup_Memory
 */
static void
AtCleanup_Memory(void)
{
	Assert(CurrentTransactionState->parent == NULL);

	/*
	 * Now that we're "out" of a transaction, have the system allocate things
	 * in the top memory context instead of per-transaction contexts.
	 */
	MemoryContextSwitchTo(TopMemoryContext);

	/*
	 * Clear the special abort context for next time.
	 */
	if (TransactionAbortContext != NULL)
		MemoryContextResetAndDeleteChildren(TransactionAbortContext);

	/*
	 * Release all transaction-local memory.
	 */
	if (TopTransactionContext != NULL)
		MemoryContextDelete(TopTransactionContext);
	TopTransactionContext = NULL;
	CurTransactionContext = NULL;
	CurrentTransactionState->curTransactionContext = NULL;
}


/* ----------------------------------------------------------------
 *						CleanupSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubCleanup_Memory
 */
static void
AtSubCleanup_Memory(void)
{
	TransactionState s = CurrentTransactionState;

	Assert(s->parent != NULL);

	/* Make sure we're not in an about-to-be-deleted context */
	MemoryContextSwitchTo(s->parent->curTransactionContext);
	CurTransactionContext = s->parent->curTransactionContext;

	/*
	 * Clear the special abort context for next time.
	 */
	if (TransactionAbortContext != NULL)
		MemoryContextResetAndDeleteChildren(TransactionAbortContext);

	/*
	 * Delete the subxact local memory contexts. Its CurTransactionContext can
	 * go too (note this also kills CurTransactionContexts from any children
	 * of the subxact).
	 */
	if (s->curTransactionContext)
		MemoryContextDelete(s->curTransactionContext);
	s->curTransactionContext = NULL;
}

/* ----------------------------------------------------------------
 *						interface routines
 * ----------------------------------------------------------------
 */

/*
 *	StartTransaction
 */
static void
StartTransaction(void)
{
	TransactionState s;

	/*
	 * Let's just make sure the state stack is empty
	 */
	s = &TopTransactionStateData;
	CurrentTransactionState = s;

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_DEFAULT)
		elog(WARNING, "StartTransaction while in %s state",
			 TransStateAsString(s->state));

	/*
	 * set the current transaction state information appropriately during
	 * start processing
	 */
	s->state = TRANS_START;
	s->transactionId = InvalidTransactionId;	/* until assigned */

	/*
	 * Make sure we've freed any old snapshot, and reset xact state variables
	 */
	FreeXactSnapshot();
	XactIsoLevel = DefaultXactIsoLevel;
	XactReadOnly = DefaultXactReadOnly;

	/*
	 * reinitialize within-transaction counters
	 */
	s->subTransactionId = TopSubTransactionId;
	currentSubTransactionId = TopSubTransactionId;
	currentCommandId = FirstCommandId;

	/*
	 * must initialize resource-management stuff first
	 */
	AtStart_Memory();
	AtStart_ResourceOwner();

	/*
	 * generate a new transaction id
	 */
	s->transactionId = GetNewTransactionId(false);

	XactLockTableInsert(s->transactionId);

	PG_TRACE1(transaction__start, s->transactionId);

	/*
	 * set transaction_timestamp() (a/k/a now()).  We want this to be the same
	 * as the first command's statement_timestamp(), so don't do a fresh
	 * GetCurrentTimestamp() call (which'd be expensive anyway).  Also,
	 * mark xactStopTimestamp as unset.
	 */
	xactStartTimestamp = stmtStartTimestamp;
	xactStopTimestamp = 0;
	pgstat_report_txn_timestamp(xactStartTimestamp);

	/*
	 * initialize current transaction state fields
	 */
	s->nestingLevel = 1;
	s->childXids = NIL;

	/*
	 * You might expect to see "s->currentUser = GetUserId();" here, but you
	 * won't because it doesn't work during startup; the userid isn't set yet
	 * during a backend's first transaction start.  We only use the
	 * currentUser field in sub-transaction state structs.
	 *
	 * prevXactReadOnly is also valid only in sub-transactions.
	 */

	/*
	 * initialize other subsystems for new transaction
	 */
	AtStart_Inval();
	AtStart_Cache();
	AfterTriggerBeginXact();

	/*
	 * done with start processing, set current transaction state to "in
	 * progress"
	 */
	s->state = TRANS_INPROGRESS;

	ShowTransactionState("StartTransaction");
}


/*
 *	CommitTransaction
 *
 * NB: if you change this routine, better look at PrepareTransaction too!
 */
static void
CommitTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	ShowTransactionState("CommitTransaction");

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_INPROGRESS)
		elog(WARNING, "CommitTransaction while in %s state",
			 TransStateAsString(s->state));
	Assert(s->parent == NULL);

	/*
	 * Do pre-commit processing (most of this stuff requires database access,
	 * and in fact could still cause an error...)
	 *
	 * It is possible for CommitHoldablePortals to invoke functions that queue
	 * deferred triggers, and it's also possible that triggers create holdable
	 * cursors.  So we have to loop until there's nothing left to do.
	 */
	for (;;)
	{
		/*
		 * Fire all currently pending deferred triggers.
		 */
		AfterTriggerFireDeferred();

		/*
		 * Convert any open holdable cursors into static portals.  If there
		 * weren't any, we are done ... otherwise loop back to check if they
		 * queued deferred triggers.  Lather, rinse, repeat.
		 */
		if (!CommitHoldablePortals())
			break;
	}

	/* Now we can shut down the deferred-trigger manager */
	AfterTriggerEndXact(true);

	/* Close any open regular cursors */
	AtCommit_Portals();

	/*
	 * Let ON COMMIT management do its thing (must happen after closing
	 * cursors, to avoid dangling-reference problems)
	 */
	PreCommit_on_commit_actions();

	/* close large objects before lower-level cleanup */
	AtEOXact_LargeObject(true);

	/* NOTIFY commit must come before lower-level cleanup */
	AtCommit_Notify();

	/*
	 * Update flat files if we changed pg_database, pg_authid or
	 * pg_auth_members.  This should be the last step before commit.
	 */
	AtEOXact_UpdateFlatFiles(true);

	/* Prevent cancel/die interrupt while cleaning up */
	HOLD_INTERRUPTS();

	/*
	 * set the current transaction state information appropriately during
	 * commit processing
	 */
	s->state = TRANS_COMMIT;

	/*
	 * Here is where we really truly commit.
	 */
	RecordTransactionCommit();

	/*----------
	 * Let others know about no transaction in progress by me. Note that
	 * this must be done _before_ releasing locks we hold and _after_
	 * RecordTransactionCommit.
	 *
	 * LWLockAcquire(ProcArrayLock) is required; consider this example:
	 *		UPDATE with xid 0 is blocked by xid 1's UPDATE.
	 *		xid 1 is doing commit while xid 2 gets snapshot.
	 * If xid 2's GetSnapshotData sees xid 1 as running then it must see
	 * xid 0 as running as well, or it will be able to see two tuple versions
	 * - one deleted by xid 1 and one inserted by xid 0.  See notes in
	 * GetSnapshotData.
	 *
	 * Note: MyProc may be null during bootstrap.
	 *----------
	 */
	if (MyProc != NULL)
	{
		/* Lock ProcArrayLock because that's what GetSnapshotData uses. */
		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
		MyProc->xid = InvalidTransactionId;
		MyProc->xmin = InvalidTransactionId;
		MyProc->inVacuum = false;		/* must be cleared with xid/xmin */

		/* Clear the subtransaction-XID cache too while holding the lock */
		MyProc->subxids.nxids = 0;
		MyProc->subxids.overflowed = false;

		LWLockRelease(ProcArrayLock);
	}

	PG_TRACE1(transaction__commit, s->transactionId);

	/*
	 * This is all post-commit cleanup.  Note that if an error is raised here,
	 * it's too late to abort the transaction.  This should be just
	 * noncritical resource releasing.
	 *
	 * The ordering of operations is not entirely random.  The idea is:
	 * release resources visible to other backends (eg, files, buffer pins);
	 * then release locks; then release backend-local resources. We want to
	 * release locks at the point where any backend waiting for us will see
	 * our transaction as being fully cleaned up.
	 *
	 * Resources that can be associated with individual queries are handled by
	 * the ResourceOwner mechanism.  The other calls here are for backend-wide
	 * state.
	 */

	CallXactCallbacks(XACT_EVENT_COMMIT);

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_BEFORE_LOCKS,
						 true, true);

	/* Check we've released all buffer pins */
	AtEOXact_Buffers(true);

	/* Clean up the relation cache */
	AtEOXact_RelationCache(true);

	/*
	 * Make catalog changes visible to all backends.  This has to happen after
	 * relcache references are dropped (see comments for
	 * AtEOXact_RelationCache), but before locks are released (if anyone is
	 * waiting for lock on a relation we've modified, we want them to know
	 * about the catalog change before they start using the relation).
	 */
	AtEOXact_Inval(true);

	/*
	 * Likewise, dropping of files deleted during the transaction is best done
	 * after releasing relcache and buffer pins.  (This is not strictly
	 * necessary during commit, since such pins should have been released
	 * already, but this ordering is definitely critical during abort.)
	 */
	smgrDoPendingDeletes(true);

	AtEOXact_MultiXact();

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_LOCKS,
						 true, true);
	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_AFTER_LOCKS,
						 true, true);

	/* Check we've released all catcache entries */
	AtEOXact_CatCache(true);

	AtEOXact_GUC(true, false);
	AtEOXact_SPI(true);
	AtEOXact_on_commit_actions(true);
	AtEOXact_Namespace(true);
	/* smgrcommit already done */
	AtEOXact_Files();
	AtEOXact_ComboCid();
	AtEOXact_HashTables(true);
	pgstat_clear_snapshot();
	pgstat_count_xact_commit();
	pgstat_report_txn_timestamp(0);

	CurrentResourceOwner = NULL;
	ResourceOwnerDelete(TopTransactionResourceOwner);
	s->curTransactionOwner = NULL;
	CurTransactionResourceOwner = NULL;
	TopTransactionResourceOwner = NULL;

	AtCommit_Memory();

	s->transactionId = InvalidTransactionId;
	s->subTransactionId = InvalidSubTransactionId;
	s->nestingLevel = 0;
	s->childXids = NIL;

	/*
	 * done with commit processing, set current transaction state back to
	 * default
	 */
	s->state = TRANS_DEFAULT;

	RESUME_INTERRUPTS();
}


/*
 *	PrepareTransaction
 *
 * NB: if you change this routine, better look at CommitTransaction too!
 */
static void
PrepareTransaction(void)
{
	TransactionState s = CurrentTransactionState;
	TransactionId xid = GetCurrentTransactionId();
	GlobalTransaction gxact;
	TimestampTz prepared_at;

	ShowTransactionState("PrepareTransaction");

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_INPROGRESS)
		elog(WARNING, "PrepareTransaction while in %s state",
			 TransStateAsString(s->state));
	Assert(s->parent == NULL);

	/*
	 * Do pre-commit processing (most of this stuff requires database access,
	 * and in fact could still cause an error...)
	 *
	 * It is possible for PrepareHoldablePortals to invoke functions that
	 * queue deferred triggers, and it's also possible that triggers create
	 * holdable cursors.  So we have to loop until there's nothing left to do.
	 */
	for (;;)
	{
		/*
		 * Fire all currently pending deferred triggers.
		 */
		AfterTriggerFireDeferred();

		/*
		 * Convert any open holdable cursors into static portals.  If there
		 * weren't any, we are done ... otherwise loop back to check if they
		 * queued deferred triggers.  Lather, rinse, repeat.
		 */
		if (!PrepareHoldablePortals())
			break;
	}

	/* Now we can shut down the deferred-trigger manager */
	AfterTriggerEndXact(true);

	/* Close any open regular cursors */
	AtCommit_Portals();

	/*
	 * Let ON COMMIT management do its thing (must happen after closing
	 * cursors, to avoid dangling-reference problems)
	 */
	PreCommit_on_commit_actions();

	/* close large objects before lower-level cleanup */
	AtEOXact_LargeObject(true);

	/* NOTIFY and flatfiles will be handled below */

	/* Prevent cancel/die interrupt while cleaning up */
	HOLD_INTERRUPTS();

	/*
	 * set the current transaction state information appropriately during
	 * prepare processing
	 */
	s->state = TRANS_PREPARE;

	prepared_at = GetCurrentTimestamp();

	/* Tell bufmgr and smgr to prepare for commit */
	BufmgrCommit();

	/*
	 * Reserve the GID for this transaction. This could fail if the requested
	 * GID is invalid or already in use.
	 */
	gxact = MarkAsPreparing(xid, prepareGID, prepared_at,
							GetUserId(), MyDatabaseId);
	prepareGID = NULL;

	/*
	 * Collect data for the 2PC state file.  Note that in general, no actual
	 * state change should happen in the called modules during this step,
	 * since it's still possible to fail before commit, and in that case we
	 * want transaction abort to be able to clean up.  (In particular, the
	 * AtPrepare routines may error out if they find cases they cannot
	 * handle.)  State cleanup should happen in the PostPrepare routines
	 * below.  However, some modules can go ahead and clear state here because
	 * they wouldn't do anything with it during abort anyway.
	 *
	 * Note: because the 2PC state file records will be replayed in the same
	 * order they are made, the order of these calls has to match the order in
	 * which we want things to happen during COMMIT PREPARED or ROLLBACK
	 * PREPARED; in particular, pay attention to whether things should happen
	 * before or after releasing the transaction's locks.
	 */
	StartPrepare(gxact);

	AtPrepare_Notify();
	AtPrepare_UpdateFlatFiles();
	AtPrepare_Inval();
	AtPrepare_Locks();

	/*
	 * Here is where we really truly prepare.
	 *
	 * We have to record transaction prepares even if we didn't make any
	 * updates, because the transaction manager might get confused if we lose
	 * a global transaction.
	 */
	EndPrepare(gxact);

	/*
	 * Now we clean up backend-internal state and release internal resources.
	 */

	/* Break the chain of back-links in the XLOG records I output */
	MyLastRecPtr.xrecoff = 0;
	MyXactMadeXLogEntry = false;
	MyXactMadeTempRelUpdate = false;

	/*
	 * Let others know about no transaction in progress by me.	This has to be
	 * done *after* the prepared transaction has been marked valid, else
	 * someone may think it is unlocked and recyclable.
	 */

	/* Lock ProcArrayLock because that's what GetSnapshotData uses. */
	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
	MyProc->xid = InvalidTransactionId;
	MyProc->xmin = InvalidTransactionId;
	MyProc->inVacuum = false;	/* must be cleared with xid/xmin */

	/* Clear the subtransaction-XID cache too while holding the lock */
	MyProc->subxids.nxids = 0;
	MyProc->subxids.overflowed = false;

	LWLockRelease(ProcArrayLock);

	/*
	 * This is all post-transaction cleanup.  Note that if an error is raised
	 * here, it's too late to abort the transaction.  This should be just
	 * noncritical resource releasing.	See notes in CommitTransaction.
	 */

	CallXactCallbacks(XACT_EVENT_PREPARE);

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_BEFORE_LOCKS,
						 true, true);

	/* Check we've released all buffer pins */
	AtEOXact_Buffers(true);

	/* Clean up the relation cache */
	AtEOXact_RelationCache(true);

	/* notify and flatfiles don't need a postprepare call */

	PostPrepare_Inval();

	PostPrepare_smgr();

	AtEOXact_MultiXact();

	PostPrepare_Locks(xid);

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_LOCKS,
						 true, true);
	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_AFTER_LOCKS,
						 true, true);

	/* Check we've released all catcache entries */
	AtEOXact_CatCache(true);

	/* PREPARE acts the same as COMMIT as far as GUC is concerned */
	AtEOXact_GUC(true, false);
	AtEOXact_SPI(true);
	AtEOXact_on_commit_actions(true);
	AtEOXact_Namespace(true);
	/* smgrcommit already done */
	AtEOXact_Files();
	AtEOXact_ComboCid();
	AtEOXact_HashTables(true);
	pgstat_clear_snapshot();

	CurrentResourceOwner = NULL;
	ResourceOwnerDelete(TopTransactionResourceOwner);
	s->curTransactionOwner = NULL;
	CurTransactionResourceOwner = NULL;
	TopTransactionResourceOwner = NULL;

	AtCommit_Memory();

	s->transactionId = InvalidTransactionId;
	s->subTransactionId = InvalidSubTransactionId;
	s->nestingLevel = 0;
	s->childXids = NIL;

	/*
	 * done with 1st phase commit processing, set current transaction state
	 * back to default
	 */
	s->state = TRANS_DEFAULT;

	RESUME_INTERRUPTS();
}


/*
 *	AbortTransaction
 */
static void
AbortTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	/* Prevent cancel/die interrupt while cleaning up */
	HOLD_INTERRUPTS();

	/* Make sure we have a valid memory context and resource owner */
	AtAbort_Memory();
	AtAbort_ResourceOwner();

	/*
	 * Release any LW locks we might be holding as quickly as possible.
	 * (Regular locks, however, must be held till we finish aborting.)
	 * Releasing LW locks is critical since we might try to grab them again
	 * while cleaning up!
	 */
	LWLockReleaseAll();

	/* Clean up buffer I/O and buffer context locks, too */
	AbortBufferIO();
	UnlockBuffers();

	/*
	 * Also clean up any open wait for lock, since the lock manager will choke
	 * if we try to wait for another lock before doing this.
	 */
	LockWaitCancel();

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_INPROGRESS && s->state != TRANS_PREPARE)
		elog(WARNING, "AbortTransaction while in %s state",
			 TransStateAsString(s->state));
	Assert(s->parent == NULL);

	/*
	 * set the current transaction state information appropriately during the
	 * abort processing
	 */
	s->state = TRANS_ABORT;

	/*
	 * Reset user id which might have been changed transiently.  We cannot use
	 * s->currentUser, since it may not be set yet; instead rely on internal
	 * state of miscinit.c.
	 *
	 * (Note: it is not necessary to restore session authorization here
	 * because that can only be changed via GUC, and GUC will take care of
	 * rolling it back if need be.	However, an error within a SECURITY
	 * DEFINER function could send control here with the wrong current
	 * userid.)
	 */
	AtAbort_UserId();

	/*
	 * do abort processing
	 */
	AfterTriggerEndXact(false);
	AtAbort_Portals();
	AtEOXact_LargeObject(false);	/* 'false' means it's abort */
	AtAbort_Notify();
	AtEOXact_UpdateFlatFiles(false);

	/*
	 * Advertise the fact that we aborted in pg_clog (assuming that we got as
	 * far as assigning an XID to advertise).
	 */
	if (TransactionIdIsValid(s->transactionId))
		RecordTransactionAbort();

	/*
	 * Let others know about no transaction in progress by me. Note that this
	 * must be done _before_ releasing locks we hold and _after_
	 * RecordTransactionAbort.
	 */
	if (MyProc != NULL)
	{
		/* Lock ProcArrayLock because that's what GetSnapshotData uses. */
		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
		MyProc->xid = InvalidTransactionId;
		MyProc->xmin = InvalidTransactionId;
		MyProc->inVacuum = false;		/* must be cleared with xid/xmin */
		MyProc->inCommit = false;		/* be sure this gets cleared */

		/* Clear the subtransaction-XID cache too while holding the lock */
		MyProc->subxids.nxids = 0;
		MyProc->subxids.overflowed = false;

		LWLockRelease(ProcArrayLock);
	}

	PG_TRACE1(transaction__abort, s->transactionId);

	/*
	 * Post-abort cleanup.	See notes in CommitTransaction() concerning
	 * ordering.
	 */

	CallXactCallbacks(XACT_EVENT_ABORT);

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_BEFORE_LOCKS,
						 false, true);
	AtEOXact_Buffers(false);
	AtEOXact_RelationCache(false);
	AtEOXact_Inval(false);
	smgrDoPendingDeletes(false);
	AtEOXact_MultiXact();
	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_LOCKS,
						 false, true);
	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_AFTER_LOCKS,
						 false, true);
	AtEOXact_CatCache(false);

	AtEOXact_GUC(false, false);
	AtEOXact_SPI(false);
	AtEOXact_on_commit_actions(false);
	AtEOXact_Namespace(false);
	smgrabort();
	AtEOXact_Files();
	AtEOXact_ComboCid();
	AtEOXact_HashTables(false);
	pgstat_clear_snapshot();
	pgstat_count_xact_rollback();
	pgstat_report_txn_timestamp(0);

	/*
	 * State remains TRANS_ABORT until CleanupTransaction().
	 */
	RESUME_INTERRUPTS();
}

/*
 *	CleanupTransaction
 */
static void
CleanupTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	/*
	 * State should still be TRANS_ABORT from AbortTransaction().
	 */
	if (s->state != TRANS_ABORT)
		elog(FATAL, "CleanupTransaction: unexpected state %s",
			 TransStateAsString(s->state));

	/*
	 * do abort cleanup processing
	 */
	AtCleanup_Portals();		/* now safe to release portal memory */

	CurrentResourceOwner = NULL;	/* and resource owner */
	if (TopTransactionResourceOwner)
		ResourceOwnerDelete(TopTransactionResourceOwner);
	s->curTransactionOwner = NULL;
	CurTransactionResourceOwner = NULL;
	TopTransactionResourceOwner = NULL;

	AtCleanup_Memory();			/* and transaction memory */

	s->transactionId = InvalidTransactionId;
	s->subTransactionId = InvalidSubTransactionId;
	s->nestingLevel = 0;
	s->childXids = NIL;

	/*
	 * done with abort processing, set current transaction state back to
	 * default
	 */
	s->state = TRANS_DEFAULT;
}

/*
 *	StartTransactionCommand
 */
void
StartTransactionCommand(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
			/*
			 * if we aren't in a transaction block, we just do our usual start
			 * transaction.
			 */
		case TBLOCK_DEFAULT:
			StartTransaction();
			s->blockState = TBLOCK_STARTED;
			break;

			/*
			 * We are somewhere in a transaction block or subtransaction and
			 * about to start a new command.  For now we do nothing, but
			 * someday we may do command-local resource initialization. (Note
			 * that any needed CommandCounterIncrement was done by the
			 * previous CommitTransactionCommand.)
			 */
		case TBLOCK_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
			break;

			/*
			 * Here we are in a failed transaction block (one of the commands
			 * caused an abort) so we do nothing but remain in the abort
			 * state.  Eventually we will get a ROLLBACK command which will
			 * get us out of this state.  (It is up to other code to ensure
			 * that no commands other than ROLLBACK will be processed in these
			 * states.)
			 */
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
			break;

			/* These cases are invalid. */
		case TBLOCK_STARTED:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(ERROR, "StartTransactionCommand: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}

	/*
	 * We must switch to CurTransactionContext before returning. This is
	 * already done if we called StartTransaction, otherwise not.
	 */
	Assert(CurTransactionContext != NULL);
	MemoryContextSwitchTo(CurTransactionContext);
}

/*
 *	CommitTransactionCommand
 */
void
CommitTransactionCommand(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
			/*
			 * This shouldn't happen, because it means the previous
			 * StartTransactionCommand didn't set the STARTED state
			 * appropriately.
			 */
		case TBLOCK_DEFAULT:
			elog(FATAL, "CommitTransactionCommand: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;

			/*
			 * If we aren't in a transaction block, just do our usual
			 * transaction commit, and return to the idle state.
			 */
		case TBLOCK_STARTED:
			CommitTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * We are completing a "BEGIN TRANSACTION" command, so we change
			 * to the "transaction block in progress" state and return.  (We
			 * assume the BEGIN did nothing to the database, so we need no
			 * CommandCounterIncrement.)
			 */
		case TBLOCK_BEGIN:
			s->blockState = TBLOCK_INPROGRESS;
			break;

			/*
			 * This is the case when we have finished executing a command
			 * someplace within a transaction block.  We increment the command
			 * counter and return.
			 */
		case TBLOCK_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
			CommandCounterIncrement();
			break;

			/*
			 * We are completing a "COMMIT" command.  Do it and return to the
			 * idle state.
			 */
		case TBLOCK_END:
			CommitTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * Here we are in the middle of a transaction block but one of the
			 * commands caused an abort so we do nothing but remain in the
			 * abort state.  Eventually we will get a ROLLBACK comand.
			 */
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
			break;

			/*
			 * Here we were in an aborted transaction block and we just got
			 * the ROLLBACK command from the user, so clean up the
			 * already-aborted transaction and return to the idle state.
			 */
		case TBLOCK_ABORT_END:
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * Here we were in a perfectly good transaction block but the user
			 * told us to ROLLBACK anyway.	We have to abort the transaction
			 * and then clean up.
			 */
		case TBLOCK_ABORT_PENDING:
			AbortTransaction();
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * We are completing a "PREPARE TRANSACTION" command.  Do it and
			 * return to the idle state.
			 */
		case TBLOCK_PREPARE:
			PrepareTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * We were just issued a SAVEPOINT inside a transaction block.
			 * Start a subtransaction.	(DefineSavepoint already did
			 * PushTransaction, so as to have someplace to put the SUBBEGIN
			 * state.)
			 */
		case TBLOCK_SUBBEGIN:
			StartSubTransaction();
			s->blockState = TBLOCK_SUBINPROGRESS;
			break;

			/*
			 * We were issued a COMMIT or RELEASE command, so we end the
			 * current subtransaction and return to the parent transaction.
			 * The parent might be ended too, so repeat till we are all the
			 * way out or find an INPROGRESS transaction.
			 */
		case TBLOCK_SUBEND:
			do
			{
				CommitSubTransaction();
				s = CurrentTransactionState;	/* changed by pop */
			} while (s->blockState == TBLOCK_SUBEND);
			/* If we had a COMMIT command, finish off the main xact too */
			if (s->blockState == TBLOCK_END)
			{
				Assert(s->parent == NULL);
				CommitTransaction();
				s->blockState = TBLOCK_DEFAULT;
			}
			else if (s->blockState == TBLOCK_PREPARE)
			{
				Assert(s->parent == NULL);
				PrepareTransaction();
				s->blockState = TBLOCK_DEFAULT;
			}
			else
			{
				Assert(s->blockState == TBLOCK_INPROGRESS ||
					   s->blockState == TBLOCK_SUBINPROGRESS);
			}
			break;

			/*
			 * The current already-failed subtransaction is ending due to a
			 * ROLLBACK or ROLLBACK TO command, so pop it and recursively
			 * examine the parent (which could be in any of several states).
			 */
		case TBLOCK_SUBABORT_END:
			CleanupSubTransaction();
			CommitTransactionCommand();
			break;

			/*
			 * As above, but it's not dead yet, so abort first.
			 */
		case TBLOCK_SUBABORT_PENDING:
			AbortSubTransaction();
			CleanupSubTransaction();
			CommitTransactionCommand();
			break;

			/*
			 * The current subtransaction is the target of a ROLLBACK TO
			 * command.  Abort and pop it, then start a new subtransaction
			 * with the same name.
			 */
		case TBLOCK_SUBRESTART:
			{
				char	   *name;
				int			savepointLevel;

				/* save name and keep Cleanup from freeing it */
				name = s->name;
				s->name = NULL;
				savepointLevel = s->savepointLevel;

				AbortSubTransaction();
				CleanupSubTransaction();

				DefineSavepoint(NULL);
				s = CurrentTransactionState;	/* changed by push */
				s->name = name;
				s->savepointLevel = savepointLevel;

				/* This is the same as TBLOCK_SUBBEGIN case */
				AssertState(s->blockState == TBLOCK_SUBBEGIN);
				StartSubTransaction();
				s->blockState = TBLOCK_SUBINPROGRESS;
			}
			break;

			/*
			 * Same as above, but the subtransaction had already failed, so we
			 * don't need AbortSubTransaction.
			 */
		case TBLOCK_SUBABORT_RESTART:
			{
				char	   *name;
				int			savepointLevel;

				/* save name and keep Cleanup from freeing it */
				name = s->name;
				s->name = NULL;
				savepointLevel = s->savepointLevel;

				CleanupSubTransaction();

				DefineSavepoint(NULL);
				s = CurrentTransactionState;	/* changed by push */
				s->name = name;
				s->savepointLevel = savepointLevel;

				/* This is the same as TBLOCK_SUBBEGIN case */
				AssertState(s->blockState == TBLOCK_SUBBEGIN);
				StartSubTransaction();
				s->blockState = TBLOCK_SUBINPROGRESS;
			}
			break;
	}
}

/*
 *	AbortCurrentTransaction
 */
void
AbortCurrentTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
		case TBLOCK_DEFAULT:
			if (s->state == TRANS_DEFAULT)
			{
				/* we are idle, so nothing to do */
			}
			else
			{
				/*
				 * We can get here after an error during transaction start
				 * (state will be TRANS_START).  Need to clean up the
				 * incompletely started transaction.  First, adjust the
				 * low-level state to suppress warning message from
				 * AbortTransaction.
				 */
				if (s->state == TRANS_START)
					s->state = TRANS_INPROGRESS;
				AbortTransaction();
				CleanupTransaction();
			}
			break;

			/*
			 * if we aren't in a transaction block, we just do the basic abort
			 * & cleanup transaction.
			 */
		case TBLOCK_STARTED:
			AbortTransaction();
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * If we are in TBLOCK_BEGIN it means something screwed up right
			 * after reading "BEGIN TRANSACTION".  We assume that the user
			 * will interpret the error as meaning the BEGIN failed to get him
			 * into a transaction block, so we should abort and return to idle
			 * state.
			 */
		case TBLOCK_BEGIN:
			AbortTransaction();
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * We are somewhere in a transaction block and we've gotten a
			 * failure, so we abort the transaction and set up the persistent
			 * ABORT state.  We will stay in ABORT until we get a ROLLBACK.
			 */
		case TBLOCK_INPROGRESS:
			AbortTransaction();
			s->blockState = TBLOCK_ABORT;
			/* CleanupTransaction happens when we exit TBLOCK_ABORT_END */
			break;

			/*
			 * Here, we failed while trying to COMMIT.	Clean up the
			 * transaction and return to idle state (we do not want to stay in
			 * the transaction).
			 */
		case TBLOCK_END:
			AbortTransaction();
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * Here, we are already in an aborted transaction state and are
			 * waiting for a ROLLBACK, but for some reason we failed again! So
			 * we just remain in the abort state.
			 */
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
			break;

			/*
			 * We are in a failed transaction and we got the ROLLBACK command.
			 * We have already aborted, we just need to cleanup and go to idle
			 * state.
			 */
		case TBLOCK_ABORT_END:
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * We are in a live transaction and we got a ROLLBACK command.
			 * Abort, cleanup, go to idle state.
			 */
		case TBLOCK_ABORT_PENDING:
			AbortTransaction();
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * Here, we failed while trying to PREPARE.  Clean up the
			 * transaction and return to idle state (we do not want to stay in
			 * the transaction).
			 */
		case TBLOCK_PREPARE:
			AbortTransaction();
			CleanupTransaction();
			s->blockState = TBLOCK_DEFAULT;
			break;

			/*
			 * We got an error inside a subtransaction.  Abort just the
			 * subtransaction, and go to the persistent SUBABORT state until
			 * we get ROLLBACK.
			 */
		case TBLOCK_SUBINPROGRESS:
			AbortSubTransaction();
			s->blockState = TBLOCK_SUBABORT;
			break;

			/*
			 * If we failed while trying to create a subtransaction, clean up
			 * the broken subtransaction and abort the parent.	The same
			 * applies if we get a failure while ending a subtransaction.
			 */
		case TBLOCK_SUBBEGIN:
		case TBLOCK_SUBEND:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
			AbortSubTransaction();
			CleanupSubTransaction();
			AbortCurrentTransaction();
			break;

			/*
			 * Same as above, except the Abort() was already done.
			 */
		case TBLOCK_SUBABORT_END:
		case TBLOCK_SUBABORT_RESTART:
			CleanupSubTransaction();
			AbortCurrentTransaction();
			break;
	}
}

/*
 *	PreventTransactionChain
 *
 *	This routine is to be called by statements that must not run inside
 *	a transaction block, typically because they have non-rollback-able
 *	side effects or do internal commits.
 *
 *	If we have already started a transaction block, issue an error; also issue
 *	an error if we appear to be running inside a user-defined function (which
 *	could issue more commands and possibly cause a failure after the statement
 *	completes).  Subtransactions are verboten too.
 *
 *	isTopLevel: passed down from ProcessUtility to determine whether we are
 *	inside a function or multi-query querystring.  (We will always fail if
 *	this is false, but it's convenient to centralize the check here instead of
 *	making callers do it.)
 *  stmtType: statement type name, for error messages.
 */
void
PreventTransactionChain(bool isTopLevel, const char *stmtType)
{
	/*
	 * xact block already started?
	 */
	if (IsTransactionBlock())
		ereport(ERROR,
				(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
		/* translator: %s represents an SQL statement name */
				 errmsg("%s cannot run inside a transaction block",
						stmtType)));

	/*
	 * subtransaction?
	 */
	if (IsSubTransaction())
		ereport(ERROR,
				(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
		/* translator: %s represents an SQL statement name */
				 errmsg("%s cannot run inside a subtransaction",
						stmtType)));

	/*
	 * inside a function call?
	 */
	if (!isTopLevel)
		ereport(ERROR,
				(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
		/* translator: %s represents an SQL statement name */
				 errmsg("%s cannot be executed from a function or multi-command string",
						stmtType)));

	/* If we got past IsTransactionBlock test, should be in default state */
	if (CurrentTransactionState->blockState != TBLOCK_DEFAULT &&
		CurrentTransactionState->blockState != TBLOCK_STARTED)
		elog(FATAL, "cannot prevent transaction chain");
	/* all okay */
}

/*
 *	RequireTransactionChain
 *
 *	This routine is to be called by statements that must run inside
 *	a transaction block, because they have no effects that persist past
 *	transaction end (and so calling them outside a transaction block
 *	is presumably an error).  DECLARE CURSOR is an example.
 *
 *	If we appear to be running inside a user-defined function, we do not
 *	issue an error, since the function could issue more commands that make
 *	use of the current statement's results.  Likewise subtransactions.
 *	Thus this is an inverse for PreventTransactionChain.
 *
 *	isTopLevel: passed down from ProcessUtility to determine whether we are
 *	inside a function.
 *	stmtType: statement type name, for error messages.
 */
void
RequireTransactionChain(bool isTopLevel, const char *stmtType)
{
	/*
	 * xact block already started?
	 */
	if (IsTransactionBlock())
		return;

	/*
	 * subtransaction?
	 */
	if (IsSubTransaction())
		return;

	/*
	 * inside a function call?
	 */
	if (!isTopLevel)
		return;

	ereport(ERROR,
			(errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
	/* translator: %s represents an SQL statement name */
			 errmsg("%s can only be used in transaction blocks",
					stmtType)));
}

/*
 *	IsInTransactionChain
 *
 *	This routine is for statements that need to behave differently inside
 *	a transaction block than when running as single commands.  ANALYZE is
 *	currently the only example.
 *
 *	isTopLevel: passed down from ProcessUtility to determine whether we are
 *	inside a function.
 */
bool
IsInTransactionChain(bool isTopLevel)
{
	/*
	 * Return true on same conditions that would make PreventTransactionChain
	 * error out
	 */
	if (IsTransactionBlock())
		return true;

	if (IsSubTransaction())
		return true;

	if (!isTopLevel)
		return true;

	if (CurrentTransactionState->blockState != TBLOCK_DEFAULT &&
		CurrentTransactionState->blockState != TBLOCK_STARTED)
		return true;

	return false;
}


/*
 * Register or deregister callback functions for start- and end-of-xact
 * operations.
 *
 * These functions are intended for use by dynamically loaded modules.
 * For built-in modules we generally just hardwire the appropriate calls
 * (mainly because it's easier to control the order that way, where needed).
 *
 * At transaction end, the callback occurs post-commit or post-abort, so the
 * callback functions can only do noncritical cleanup.
 */
void
RegisterXactCallback(XactCallback callback, void *arg)
{
	XactCallbackItem *item;

	item = (XactCallbackItem *)
		MemoryContextAlloc(TopMemoryContext, sizeof(XactCallbackItem));
	item->callback = callback;
	item->arg = arg;
	item->next = Xact_callbacks;
	Xact_callbacks = item;
}

void
UnregisterXactCallback(XactCallback callback, void *arg)
{
	XactCallbackItem *item;
	XactCallbackItem *prev;

	prev = NULL;
	for (item = Xact_callbacks; item; prev = item, item = item->next)
	{
		if (item->callback == callback && item->arg == arg)
		{
			if (prev)
				prev->next = item->next;
			else
				Xact_callbacks = item->next;
			pfree(item);
			break;
		}
	}
}

static void
CallXactCallbacks(XactEvent event)
{
	XactCallbackItem *item;

	for (item = Xact_callbacks; item; item = item->next)
		(*item->callback) (event, item->arg);
}


/*
 * Register or deregister callback functions for start- and end-of-subxact
 * operations.
 *
 * Pretty much same as above, but for subtransaction events.
 *
 * At subtransaction end, the callback occurs post-subcommit or post-subabort,
 * so the callback functions can only do noncritical cleanup.  At
 * subtransaction start, the callback is called when the subtransaction has
 * finished initializing.
 */
void
RegisterSubXactCallback(SubXactCallback callback, void *arg)
{
	SubXactCallbackItem *item;

	item = (SubXactCallbackItem *)
		MemoryContextAlloc(TopMemoryContext, sizeof(SubXactCallbackItem));
	item->callback = callback;
	item->arg = arg;
	item->next = SubXact_callbacks;
	SubXact_callbacks = item;
}

void
UnregisterSubXactCallback(SubXactCallback callback, void *arg)
{
	SubXactCallbackItem *item;
	SubXactCallbackItem *prev;

	prev = NULL;
	for (item = SubXact_callbacks; item; prev = item, item = item->next)
	{
		if (item->callback == callback && item->arg == arg)
		{
			if (prev)
				prev->next = item->next;
			else
				SubXact_callbacks = item->next;
			pfree(item);
			break;
		}
	}
}

static void
CallSubXactCallbacks(SubXactEvent event,
					 SubTransactionId mySubid,
					 SubTransactionId parentSubid)
{
	SubXactCallbackItem *item;

	for (item = SubXact_callbacks; item; item = item->next)
		(*item->callback) (event, mySubid, parentSubid, item->arg);
}


/* ----------------------------------------------------------------
 *					   transaction block support
 * ----------------------------------------------------------------
 */

/*
 *	BeginTransactionBlock
 *		This executes a BEGIN command.
 */
void
BeginTransactionBlock(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
			/*
			 * We are not inside a transaction block, so allow one to begin.
			 */
		case TBLOCK_STARTED:
			s->blockState = TBLOCK_BEGIN;
			break;

			/*
			 * Already a transaction block in progress.
			 */
		case TBLOCK_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
			ereport(WARNING,
					(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
					 errmsg("there is already a transaction in progress")));
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "BeginTransactionBlock: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}
}

/*
 *	PrepareTransactionBlock
 *		This executes a PREPARE command.
 *
 * Since PREPARE may actually do a ROLLBACK, the result indicates what
 * happened: TRUE for PREPARE, FALSE for ROLLBACK.
 *
 * Note that we don't actually do anything here except change blockState.
 * The real work will be done in the upcoming PrepareTransaction().
 * We do it this way because it's not convenient to change memory context,
 * resource owner, etc while executing inside a Portal.
 */
bool
PrepareTransactionBlock(char *gid)
{
	TransactionState s;
	bool		result;

	/* Set up to commit the current transaction */
	result = EndTransactionBlock();

	/* If successful, change outer tblock state to PREPARE */
	if (result)
	{
		s = CurrentTransactionState;

		while (s->parent != NULL)
			s = s->parent;

		if (s->blockState == TBLOCK_END)
		{
			/* Save GID where PrepareTransaction can find it again */
			prepareGID = MemoryContextStrdup(TopTransactionContext, gid);

			s->blockState = TBLOCK_PREPARE;
		}
		else
		{
			/*
			 * ignore case where we are not in a transaction;
			 * EndTransactionBlock already issued a warning.
			 */
			Assert(s->blockState == TBLOCK_STARTED);
			/* Don't send back a PREPARE result tag... */
			result = false;
		}
	}

	return result;
}

/*
 *	EndTransactionBlock
 *		This executes a COMMIT command.
 *
 * Since COMMIT may actually do a ROLLBACK, the result indicates what
 * happened: TRUE for COMMIT, FALSE for ROLLBACK.
 *
 * Note that we don't actually do anything here except change blockState.
 * The real work will be done in the upcoming CommitTransactionCommand().
 * We do it this way because it's not convenient to change memory context,
 * resource owner, etc while executing inside a Portal.
 */
bool
EndTransactionBlock(void)
{
	TransactionState s = CurrentTransactionState;
	bool		result = false;

	switch (s->blockState)
	{
			/*
			 * We are in a transaction block, so tell CommitTransactionCommand
			 * to COMMIT.
			 */
		case TBLOCK_INPROGRESS:
			s->blockState = TBLOCK_END;
			result = true;
			break;

			/*
			 * We are in a failed transaction block.  Tell
			 * CommitTransactionCommand it's time to exit the block.
			 */
		case TBLOCK_ABORT:
			s->blockState = TBLOCK_ABORT_END;
			break;

			/*
			 * We are in a live subtransaction block.  Set up to subcommit all
			 * open subtransactions and then commit the main transaction.
			 */
		case TBLOCK_SUBINPROGRESS:
			while (s->parent != NULL)
			{
				if (s->blockState == TBLOCK_SUBINPROGRESS)
					s->blockState = TBLOCK_SUBEND;
				else
					elog(FATAL, "EndTransactionBlock: unexpected state %s",
						 BlockStateAsString(s->blockState));
				s = s->parent;
			}
			if (s->blockState == TBLOCK_INPROGRESS)
				s->blockState = TBLOCK_END;
			else
				elog(FATAL, "EndTransactionBlock: unexpected state %s",
					 BlockStateAsString(s->blockState));
			result = true;
			break;

			/*
			 * Here we are inside an aborted subtransaction.  Treat the COMMIT
			 * as ROLLBACK: set up to abort everything and exit the main
			 * transaction.
			 */
		case TBLOCK_SUBABORT:
			while (s->parent != NULL)
			{
				if (s->blockState == TBLOCK_SUBINPROGRESS)
					s->blockState = TBLOCK_SUBABORT_PENDING;
				else if (s->blockState == TBLOCK_SUBABORT)
					s->blockState = TBLOCK_SUBABORT_END;
				else
					elog(FATAL, "EndTransactionBlock: unexpected state %s",
						 BlockStateAsString(s->blockState));
				s = s->parent;
			}
			if (s->blockState == TBLOCK_INPROGRESS)
				s->blockState = TBLOCK_ABORT_PENDING;
			else if (s->blockState == TBLOCK_ABORT)
				s->blockState = TBLOCK_ABORT_END;
			else
				elog(FATAL, "EndTransactionBlock: unexpected state %s",
					 BlockStateAsString(s->blockState));
			break;

			/*
			 * The user issued COMMIT when not inside a transaction.  Issue a
			 * WARNING, staying in TBLOCK_STARTED state.  The upcoming call to
			 * CommitTransactionCommand() will then close the transaction and
			 * put us back into the default state.
			 */
		case TBLOCK_STARTED:
			ereport(WARNING,
					(errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
					 errmsg("there is no transaction in progress")));
			result = true;
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "EndTransactionBlock: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}

	return result;
}

/*
 *	UserAbortTransactionBlock
 *		This executes a ROLLBACK command.
 *
 * As above, we don't actually do anything here except change blockState.
 */
void
UserAbortTransactionBlock(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
			/*
			 * We are inside a transaction block and we got a ROLLBACK command
			 * from the user, so tell CommitTransactionCommand to abort and
			 * exit the transaction block.
			 */
		case TBLOCK_INPROGRESS:
			s->blockState = TBLOCK_ABORT_PENDING;
			break;

			/*
			 * We are inside a failed transaction block and we got a ROLLBACK
			 * command from the user.  Abort processing is already done, so
			 * CommitTransactionCommand just has to cleanup and go back to
			 * idle state.
			 */
		case TBLOCK_ABORT:
			s->blockState = TBLOCK_ABORT_END;
			break;

			/*
			 * We are inside a subtransaction.	Mark everything up to top
			 * level as exitable.
			 */
		case TBLOCK_SUBINPROGRESS:
		case TBLOCK_SUBABORT:
			while (s->parent != NULL)
			{
				if (s->blockState == TBLOCK_SUBINPROGRESS)
					s->blockState = TBLOCK_SUBABORT_PENDING;
				else if (s->blockState == TBLOCK_SUBABORT)
					s->blockState = TBLOCK_SUBABORT_END;
				else
					elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
						 BlockStateAsString(s->blockState));
				s = s->parent;
			}
			if (s->blockState == TBLOCK_INPROGRESS)
				s->blockState = TBLOCK_ABORT_PENDING;
			else if (s->blockState == TBLOCK_ABORT)
				s->blockState = TBLOCK_ABORT_END;
			else
				elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
					 BlockStateAsString(s->blockState));
			break;

			/*
			 * The user issued ABORT when not inside a transaction. Issue a
			 * WARNING and go to abort state.  The upcoming call to
			 * CommitTransactionCommand() will then put us back into the
			 * default state.
			 */
		case TBLOCK_STARTED:
			ereport(WARNING,
					(errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
					 errmsg("there is no transaction in progress")));
			s->blockState = TBLOCK_ABORT_PENDING;
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}
}

/*
 * DefineSavepoint
 *		This executes a SAVEPOINT command.
 */
void
DefineSavepoint(char *name)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
		case TBLOCK_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
			/* Normal subtransaction start */
			PushTransaction();
			s = CurrentTransactionState;		/* changed by push */

			/*
			 * Savepoint names, like the TransactionState block itself, live
			 * in TopTransactionContext.
			 */
			if (name)
				s->name = MemoryContextStrdup(TopTransactionContext, name);
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_STARTED:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "DefineSavepoint: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}
}

/*
 * ReleaseSavepoint
 *		This executes a RELEASE command.
 *
 * As above, we don't actually do anything here except change blockState.
 */
void
ReleaseSavepoint(List *options)
{
	TransactionState s = CurrentTransactionState;
	TransactionState target,
				xact;
	ListCell   *cell;
	char	   *name = NULL;

	switch (s->blockState)
	{
			/*
			 * We can't rollback to a savepoint if there is no savepoint
			 * defined.
			 */
		case TBLOCK_INPROGRESS:
			ereport(ERROR,
					(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
					 errmsg("no such savepoint")));
			break;

			/*
			 * We are in a non-aborted subtransaction.	This is the only valid
			 * case.
			 */
		case TBLOCK_SUBINPROGRESS:
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_STARTED:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "ReleaseSavepoint: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}

	foreach(cell, options)
	{
		DefElem    *elem = lfirst(cell);

		if (strcmp(elem->defname, "savepoint_name") == 0)
			name = strVal(elem->arg);
	}

	Assert(PointerIsValid(name));

	for (target = s; PointerIsValid(target); target = target->parent)
	{
		if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)
			break;
	}

	if (!PointerIsValid(target))
		ereport(ERROR,
				(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
				 errmsg("no such savepoint")));

	/* disallow crossing savepoint level boundaries */
	if (target->savepointLevel != s->savepointLevel)
		ereport(ERROR,
				(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
				 errmsg("no such savepoint")));

	/*
	 * Mark "commit pending" all subtransactions up to the target
	 * subtransaction.	The actual commits will happen when control gets to
	 * CommitTransactionCommand.
	 */
	xact = CurrentTransactionState;
	for (;;)
	{
		Assert(xact->blockState == TBLOCK_SUBINPROGRESS);
		xact->blockState = TBLOCK_SUBEND;
		if (xact == target)
			break;
		xact = xact->parent;
		Assert(PointerIsValid(xact));
	}
}

/*
 * RollbackToSavepoint
 *		This executes a ROLLBACK TO <savepoint> command.
 *
 * As above, we don't actually do anything here except change blockState.
 */
void
RollbackToSavepoint(List *options)
{
	TransactionState s = CurrentTransactionState;
	TransactionState target,
				xact;
	ListCell   *cell;
	char	   *name = NULL;

	switch (s->blockState)
	{
			/*
			 * We can't rollback to a savepoint if there is no savepoint
			 * defined.
			 */
		case TBLOCK_INPROGRESS:
		case TBLOCK_ABORT:
			ereport(ERROR,
					(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
					 errmsg("no such savepoint")));
			break;

			/*
			 * There is at least one savepoint, so proceed.
			 */
		case TBLOCK_SUBINPROGRESS:
		case TBLOCK_SUBABORT:
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_STARTED:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "RollbackToSavepoint: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}

	foreach(cell, options)
	{
		DefElem    *elem = lfirst(cell);

		if (strcmp(elem->defname, "savepoint_name") == 0)
			name = strVal(elem->arg);
	}

	Assert(PointerIsValid(name));

	for (target = s; PointerIsValid(target); target = target->parent)
	{
		if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)
			break;
	}

	if (!PointerIsValid(target))
		ereport(ERROR,
				(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
				 errmsg("no such savepoint")));

	/* disallow crossing savepoint level boundaries */
	if (target->savepointLevel != s->savepointLevel)
		ereport(ERROR,
				(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
				 errmsg("no such savepoint")));

	/*
	 * Mark "abort pending" all subtransactions up to the target
	 * subtransaction.	The actual aborts will happen when control gets to
	 * CommitTransactionCommand.
	 */
	xact = CurrentTransactionState;
	for (;;)
	{
		if (xact == target)
			break;
		if (xact->blockState == TBLOCK_SUBINPROGRESS)
			xact->blockState = TBLOCK_SUBABORT_PENDING;
		else if (xact->blockState == TBLOCK_SUBABORT)
			xact->blockState = TBLOCK_SUBABORT_END;
		else
			elog(FATAL, "RollbackToSavepoint: unexpected state %s",
				 BlockStateAsString(xact->blockState));
		xact = xact->parent;
		Assert(PointerIsValid(xact));
	}

	/* And mark the target as "restart pending" */
	if (xact->blockState == TBLOCK_SUBINPROGRESS)
		xact->blockState = TBLOCK_SUBRESTART;
	else if (xact->blockState == TBLOCK_SUBABORT)
		xact->blockState = TBLOCK_SUBABORT_RESTART;
	else
		elog(FATAL, "RollbackToSavepoint: unexpected state %s",
			 BlockStateAsString(xact->blockState));
}

/*
 * BeginInternalSubTransaction
 *		This is the same as DefineSavepoint except it allows TBLOCK_STARTED
 *		state, and therefore it can safely be used in a function that might
 *		be called when not inside a BEGIN block.  Also, we automatically
 *		cycle through CommitTransactionCommand/StartTransactionCommand
 *		instead of expecting the caller to do it.
 */
void
BeginInternalSubTransaction(char *name)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
		case TBLOCK_STARTED:
		case TBLOCK_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
			/* Normal subtransaction start */
			PushTransaction();
			s = CurrentTransactionState;		/* changed by push */

			/*
			 * Savepoint names, like the TransactionState block itself, live
			 * in TopTransactionContext.
			 */
			if (name)
				s->name = MemoryContextStrdup(TopTransactionContext, name);
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "BeginInternalSubTransaction: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}

	CommitTransactionCommand();
	StartTransactionCommand();
}

/*
 * ReleaseCurrentSubTransaction
 *
 * RELEASE (ie, commit) the innermost subtransaction, regardless of its
 * savepoint name (if any).
 * NB: do NOT use CommitTransactionCommand/StartTransactionCommand with this.
 */
void
ReleaseCurrentSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->blockState != TBLOCK_SUBINPROGRESS)
		elog(ERROR, "ReleaseCurrentSubTransaction: unexpected state %s",
			 BlockStateAsString(s->blockState));
	Assert(s->state == TRANS_INPROGRESS);
	MemoryContextSwitchTo(CurTransactionContext);
	CommitSubTransaction();
	s = CurrentTransactionState;	/* changed by pop */
	Assert(s->state == TRANS_INPROGRESS);
}

/*
 * RollbackAndReleaseCurrentSubTransaction
 *
 * ROLLBACK and RELEASE (ie, abort) the innermost subtransaction, regardless
 * of its savepoint name (if any).
 * NB: do NOT use CommitTransactionCommand/StartTransactionCommand with this.
 */
void
RollbackAndReleaseCurrentSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
			/* Must be in a subtransaction */
		case TBLOCK_SUBINPROGRESS:
		case TBLOCK_SUBABORT:
			break;

			/* These cases are invalid. */
		case TBLOCK_DEFAULT:
		case TBLOCK_STARTED:
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_INPROGRESS:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_ABORT:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
		case TBLOCK_PREPARE:
			elog(FATAL, "RollbackAndReleaseCurrentSubTransaction: unexpected state %s",
				 BlockStateAsString(s->blockState));
			break;
	}

	/*
	 * Abort the current subtransaction, if needed.
	 */
	if (s->blockState == TBLOCK_SUBINPROGRESS)
		AbortSubTransaction();

	/* And clean it up, too */
	CleanupSubTransaction();

	s = CurrentTransactionState;	/* changed by pop */
	AssertState(s->blockState == TBLOCK_SUBINPROGRESS ||
				s->blockState == TBLOCK_INPROGRESS ||
				s->blockState == TBLOCK_STARTED);
}

/*
 *	AbortOutOfAnyTransaction
 *
 *	This routine is provided for error recovery purposes.  It aborts any
 *	active transaction or transaction block, leaving the system in a known
 *	idle state.
 */
void
AbortOutOfAnyTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	/*
	 * Get out of any transaction or nested transaction
	 */
	do
	{
		switch (s->blockState)
		{
			case TBLOCK_DEFAULT:
				/* Not in a transaction, do nothing */
				break;
			case TBLOCK_STARTED:
			case TBLOCK_BEGIN:
			case TBLOCK_INPROGRESS:
			case TBLOCK_END:
			case TBLOCK_ABORT_PENDING:
			case TBLOCK_PREPARE:
				/* In a transaction, so clean up */
				AbortTransaction();
				CleanupTransaction();
				s->blockState = TBLOCK_DEFAULT;
				break;
			case TBLOCK_ABORT:
			case TBLOCK_ABORT_END:
				/* AbortTransaction already done, still need Cleanup */
				CleanupTransaction();
				s->blockState = TBLOCK_DEFAULT;
				break;

				/*
				 * In a subtransaction, so clean it up and abort parent too
				 */
			case TBLOCK_SUBBEGIN:
			case TBLOCK_SUBINPROGRESS:
			case TBLOCK_SUBEND:
			case TBLOCK_SUBABORT_PENDING:
			case TBLOCK_SUBRESTART:
				AbortSubTransaction();
				CleanupSubTransaction();
				s = CurrentTransactionState;	/* changed by pop */
				break;

			case TBLOCK_SUBABORT:
			case TBLOCK_SUBABORT_END:
			case TBLOCK_SUBABORT_RESTART:
				/* As above, but AbortSubTransaction already done */
				CleanupSubTransaction();
				s = CurrentTransactionState;	/* changed by pop */
				break;
		}
	} while (s->blockState != TBLOCK_DEFAULT);

	/* Should be out of all subxacts now */
	Assert(s->parent == NULL);
}

/*
 * IsTransactionBlock --- are we within a transaction block?
 */
bool
IsTransactionBlock(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->blockState == TBLOCK_DEFAULT || s->blockState == TBLOCK_STARTED)
		return false;

	return true;
}

/*
 * IsTransactionOrTransactionBlock --- are we within either a transaction
 * or a transaction block?	(The backend is only really "idle" when this
 * returns false.)
 *
 * This should match up with IsTransactionBlock and IsTransactionState.
 */
bool
IsTransactionOrTransactionBlock(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->blockState == TBLOCK_DEFAULT)
		return false;

	return true;
}

/*
 * TransactionBlockStatusCode - return status code to send in ReadyForQuery
 */
char
TransactionBlockStatusCode(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->blockState)
	{
		case TBLOCK_DEFAULT:
		case TBLOCK_STARTED:
			return 'I';			/* idle --- not in transaction */
		case TBLOCK_BEGIN:
		case TBLOCK_SUBBEGIN:
		case TBLOCK_INPROGRESS:
		case TBLOCK_SUBINPROGRESS:
		case TBLOCK_END:
		case TBLOCK_SUBEND:
		case TBLOCK_PREPARE:
			return 'T';			/* in transaction */
		case TBLOCK_ABORT:
		case TBLOCK_SUBABORT:
		case TBLOCK_ABORT_END:
		case TBLOCK_SUBABORT_END:
		case TBLOCK_ABORT_PENDING:
		case TBLOCK_SUBABORT_PENDING:
		case TBLOCK_SUBRESTART:
		case TBLOCK_SUBABORT_RESTART:
			return 'E';			/* in failed transaction */
	}

	/* should never get here */
	elog(FATAL, "invalid transaction block state: %s",
		 BlockStateAsString(s->blockState));
	return 0;					/* keep compiler quiet */
}

/*
 * IsSubTransaction
 */
bool
IsSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->nestingLevel >= 2)
		return true;

	return false;
}

/*
 * StartSubTransaction
 *
 * If you're wondering why this is separate from PushTransaction: it's because
 * we can't conveniently do this stuff right inside DefineSavepoint.  The
 * SAVEPOINT utility command will be executed inside a Portal, and if we
 * muck with CurrentMemoryContext or CurrentResourceOwner then exit from
 * the Portal will undo those settings.  So we make DefineSavepoint just
 * push a dummy transaction block, and when control returns to the main
 * idle loop, CommitTransactionCommand will be called, and we'll come here
 * to finish starting the subtransaction.
 */
static void
StartSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->state != TRANS_DEFAULT)
		elog(WARNING, "StartSubTransaction while in %s state",
			 TransStateAsString(s->state));

	s->state = TRANS_START;

	/*
	 * Initialize subsystems for new subtransaction
	 *
	 * must initialize resource-management stuff first
	 */
	AtSubStart_Memory();
	AtSubStart_ResourceOwner();
	AtSubStart_Inval();
	AtSubStart_Notify();
	AfterTriggerBeginSubXact();

	s->state = TRANS_INPROGRESS;

	/*
	 * Call start-of-subxact callbacks
	 */
	CallSubXactCallbacks(SUBXACT_EVENT_START_SUB, s->subTransactionId,
						 s->parent->subTransactionId);

	ShowTransactionState("StartSubTransaction");
}

/*
 * CommitSubTransaction
 *
 *	The caller has to make sure to always reassign CurrentTransactionState
 *	if it has a local pointer to it after calling this function.
 */
static void
CommitSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	ShowTransactionState("CommitSubTransaction");

	if (s->state != TRANS_INPROGRESS)
		elog(WARNING, "CommitSubTransaction while in %s state",
			 TransStateAsString(s->state));

	/* Pre-commit processing goes here -- nothing to do at the moment */

	s->state = TRANS_COMMIT;

	/* Must CCI to ensure commands of subtransaction are seen as done */
	CommandCounterIncrement();

	/* Mark subtransaction as subcommitted */
	if (TransactionIdIsValid(s->transactionId))
	{
		RecordSubTransactionCommit();
		AtSubCommit_childXids();
	}

	/* Post-commit cleanup */
	AfterTriggerEndSubXact(true);
	AtSubCommit_Portals(s->subTransactionId,
						s->parent->subTransactionId,
						s->parent->curTransactionOwner);
	AtEOSubXact_LargeObject(true, s->subTransactionId,
							s->parent->subTransactionId);
	AtSubCommit_Notify();
	AtEOSubXact_UpdateFlatFiles(true, s->subTransactionId,
								s->parent->subTransactionId);

	CallSubXactCallbacks(SUBXACT_EVENT_COMMIT_SUB, s->subTransactionId,
						 s->parent->subTransactionId);

	ResourceOwnerRelease(s->curTransactionOwner,
						 RESOURCE_RELEASE_BEFORE_LOCKS,
						 true, false);
	AtEOSubXact_RelationCache(true, s->subTransactionId,
							  s->parent->subTransactionId);
	AtEOSubXact_Inval(true);
	AtSubCommit_smgr();

	/*
	 * The only lock we actually release here is the subtransaction XID lock.
	 * The rest just get transferred to the parent resource owner.
	 */
	CurrentResourceOwner = s->curTransactionOwner;
	if (TransactionIdIsValid(s->transactionId))
		XactLockTableDelete(s->transactionId);

	ResourceOwnerRelease(s->curTransactionOwner,
						 RESOURCE_RELEASE_LOCKS,
						 true, false);
	ResourceOwnerRelease(s->curTransactionOwner,
						 RESOURCE_RELEASE_AFTER_LOCKS,
						 true, false);

	AtEOXact_GUC(true, true);
	AtEOSubXact_SPI(true, s->subTransactionId);
	AtEOSubXact_on_commit_actions(true, s->subTransactionId,
								  s->parent->subTransactionId);
	AtEOSubXact_Namespace(true, s->subTransactionId,
						  s->parent->subTransactionId);
	AtEOSubXact_Files(true, s->subTransactionId,
					  s->parent->subTransactionId);
	AtEOSubXact_HashTables(true, s->nestingLevel);

	/*
	 * We need to restore the upper transaction's read-only state, in case the
	 * upper is read-write while the child is read-only; GUC will incorrectly
	 * think it should leave the child state in place.
	 */
	XactReadOnly = s->prevXactReadOnly;

	CurrentResourceOwner = s->parent->curTransactionOwner;
	CurTransactionResourceOwner = s->parent->curTransactionOwner;
	ResourceOwnerDelete(s->curTransactionOwner);
	s->curTransactionOwner = NULL;

	AtSubCommit_Memory();

	s->state = TRANS_DEFAULT;

	PopTransaction();
}

/*
 * AbortSubTransaction
 */
static void
AbortSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	/* Prevent cancel/die interrupt while cleaning up */
	HOLD_INTERRUPTS();

	/* Make sure we have a valid memory context and resource owner */
	AtSubAbort_Memory();
	AtSubAbort_ResourceOwner();

	/*
	 * Release any LW locks we might be holding as quickly as possible.
	 * (Regular locks, however, must be held till we finish aborting.)
	 * Releasing LW locks is critical since we might try to grab them again
	 * while cleaning up!
	 *
	 * FIXME This may be incorrect --- Are there some locks we should keep?
	 * Buffer locks, for example?  I don't think so but I'm not sure.
	 */
	LWLockReleaseAll();

	AbortBufferIO();
	UnlockBuffers();

	LockWaitCancel();

	/*
	 * check the current transaction state
	 */
	ShowTransactionState("AbortSubTransaction");

	if (s->state != TRANS_INPROGRESS)
		elog(WARNING, "AbortSubTransaction while in %s state",
			 TransStateAsString(s->state));

	s->state = TRANS_ABORT;

	/*
	 * We can skip all this stuff if the subxact failed before creating a
	 * ResourceOwner...
	 */
	if (s->curTransactionOwner)
	{
		AfterTriggerEndSubXact(false);
		AtSubAbort_Portals(s->subTransactionId,
						   s->parent->subTransactionId,
						   s->parent->curTransactionOwner);
		AtEOSubXact_LargeObject(false, s->subTransactionId,
								s->parent->subTransactionId);
		AtSubAbort_Notify();
		AtEOSubXact_UpdateFlatFiles(false, s->subTransactionId,
									s->parent->subTransactionId);

		/* Advertise the fact that we aborted in pg_clog. */
		if (TransactionIdIsValid(s->transactionId))
		{
			RecordSubTransactionAbort();
			AtSubAbort_childXids();
		}

		/* Post-abort cleanup */
		CallSubXactCallbacks(SUBXACT_EVENT_ABORT_SUB, s->subTransactionId,
							 s->parent->subTransactionId);

		ResourceOwnerRelease(s->curTransactionOwner,
							 RESOURCE_RELEASE_BEFORE_LOCKS,
							 false, false);
		AtEOSubXact_RelationCache(false, s->subTransactionId,
								  s->parent->subTransactionId);
		AtEOSubXact_Inval(false);
		AtSubAbort_smgr();
		ResourceOwnerRelease(s->curTransactionOwner,
							 RESOURCE_RELEASE_LOCKS,
							 false, false);
		ResourceOwnerRelease(s->curTransactionOwner,
							 RESOURCE_RELEASE_AFTER_LOCKS,
							 false, false);

		AtEOXact_GUC(false, true);
		AtEOSubXact_SPI(false, s->subTransactionId);
		AtEOSubXact_on_commit_actions(false, s->subTransactionId,
									  s->parent->subTransactionId);
		AtEOSubXact_Namespace(false, s->subTransactionId,
							  s->parent->subTransactionId);
		AtEOSubXact_Files(false, s->subTransactionId,
						  s->parent->subTransactionId);
		AtEOSubXact_HashTables(false, s->nestingLevel);
	}

	/*
	 * Reset user id which might have been changed transiently.  Here we want
	 * to restore to the userid that was current at subxact entry. (As in
	 * AbortTransaction, we need not worry about the session userid.)
	 *
	 * Must do this after AtEOXact_GUC to handle the case where we entered the
	 * subxact inside a SECURITY DEFINER function (hence current and session
	 * userids were different) and then session auth was changed inside the
	 * subxact.  GUC will reset both current and session userids to the
	 * entry-time session userid.  This is right in every other scenario so it
	 * seems simplest to let GUC do that and fix it here.
	 */
	SetUserId(s->currentUser);

	/*
	 * Restore the upper transaction's read-only state, too.  This should be
	 * redundant with GUC's cleanup but we may as well do it for consistency
	 * with the commit case.
	 */
	XactReadOnly = s->prevXactReadOnly;

	RESUME_INTERRUPTS();
}

/*
 * CleanupSubTransaction
 *
 *	The caller has to make sure to always reassign CurrentTransactionState
 *	if it has a local pointer to it after calling this function.
 */
static void
CleanupSubTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	ShowTransactionState("CleanupSubTransaction");

	if (s->state != TRANS_ABORT)
		elog(WARNING, "CleanupSubTransaction while in %s state",
			 TransStateAsString(s->state));

	AtSubCleanup_Portals(s->subTransactionId);

	CurrentResourceOwner = s->parent->curTransactionOwner;
	CurTransactionResourceOwner = s->parent->curTransactionOwner;
	if (s->curTransactionOwner)
		ResourceOwnerDelete(s->curTransactionOwner);
	s->curTransactionOwner = NULL;

	AtSubCleanup_Memory();

	s->state = TRANS_DEFAULT;

	PopTransaction();
}

/*
 * PushTransaction
 *		Create transaction state stack entry for a subtransaction
 *
 *	The caller has to make sure to always reassign CurrentTransactionState
 *	if it has a local pointer to it after calling this function.
 */
static void
PushTransaction(void)
{
	TransactionState p = CurrentTransactionState;
	TransactionState s;
	Oid			currentUser;

	/*
	 * At present, GetUserId cannot fail, but let's not assume that.  Get the
	 * ID before entering the critical code sequence.
	 */
	currentUser = GetUserId();

	/*
	 * We keep subtransaction state nodes in TopTransactionContext.
	 */
	s = (TransactionState)
		MemoryContextAllocZero(TopTransactionContext,
							   sizeof(TransactionStateData));

	/*
	 * Assign a subtransaction ID, watching out for counter wraparound.
	 */
	currentSubTransactionId += 1;
	if (currentSubTransactionId == InvalidSubTransactionId)
	{
		currentSubTransactionId -= 1;
		pfree(s);
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("cannot have more than 2^32-1 subtransactions in a transaction")));
	}

	/*
	 * We can now stack a minimally valid subtransaction without fear of
	 * failure.
	 */
	s->transactionId = InvalidTransactionId;	/* until assigned */
	s->subTransactionId = currentSubTransactionId;
	s->parent = p;
	s->nestingLevel = p->nestingLevel + 1;
	s->savepointLevel = p->savepointLevel;
	s->state = TRANS_DEFAULT;
	s->blockState = TBLOCK_SUBBEGIN;
	s->currentUser = currentUser;
	s->prevXactReadOnly = XactReadOnly;

	CurrentTransactionState = s;

	/*
	 * AbortSubTransaction and CleanupSubTransaction have to be able to cope
	 * with the subtransaction from here on out; in particular they should not
	 * assume that it necessarily has a transaction context, resource owner,
	 * or XID.
	 */
}

/*
 * PopTransaction
 *		Pop back to parent transaction state
 *
 *	The caller has to make sure to always reassign CurrentTransactionState
 *	if it has a local pointer to it after calling this function.
 */
static void
PopTransaction(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->state != TRANS_DEFAULT)
		elog(WARNING, "PopTransaction while in %s state",
			 TransStateAsString(s->state));

	if (s->parent == NULL)
		elog(FATAL, "PopTransaction with no parent");

	CurrentTransactionState = s->parent;

	/* Let's just make sure CurTransactionContext is good */
	CurTransactionContext = s->parent->curTransactionContext;
	MemoryContextSwitchTo(CurTransactionContext);

	/* Ditto for ResourceOwner links */
	CurTransactionResourceOwner = s->parent->curTransactionOwner;
	CurrentResourceOwner = s->parent->curTransactionOwner;

	/* Free the old child structure */
	if (s->name)
		pfree(s->name);
	pfree(s);
}

/*
 * ShowTransactionState
 *		Debug support
 */
static void
ShowTransactionState(const char *str)
{
	/* skip work if message will definitely not be printed */
	if (log_min_messages <= DEBUG3 || client_min_messages <= DEBUG3)
	{
		elog(DEBUG3, "%s", str);
		ShowTransactionStateRec(CurrentTransactionState);
	}
}

/*
 * ShowTransactionStateRec
 *		Recursive subroutine for ShowTransactionState
 */
static void
ShowTransactionStateRec(TransactionState s)
{
	if (s->parent)
		ShowTransactionStateRec(s->parent);

	/* use ereport to suppress computation if msg will not be printed */
	ereport(DEBUG3,
			(errmsg_internal("name: %s; blockState: %13s; state: %7s, xid/subid/cid: %u/%u/%u, nestlvl: %d, children: %s",
							 PointerIsValid(s->name) ? s->name : "unnamed",
							 BlockStateAsString(s->blockState),
							 TransStateAsString(s->state),
							 (unsigned int) s->transactionId,
							 (unsigned int) s->subTransactionId,
							 (unsigned int) currentCommandId,
							 s->nestingLevel,
							 nodeToString(s->childXids))));
}

/*
 * BlockStateAsString
 *		Debug support
 */
static const char *
BlockStateAsString(TBlockState blockState)
{
	switch (blockState)
	{
		case TBLOCK_DEFAULT:
			return "DEFAULT";
		case TBLOCK_STARTED:
			return "STARTED";
		case TBLOCK_BEGIN:
			return "BEGIN";
		case TBLOCK_INPROGRESS:
			return "INPROGRESS";
		case TBLOCK_END:
			return "END";
		case TBLOCK_ABORT:
			return "ABORT";
		case TBLOCK_ABORT_END:
			return "ABORT END";
		case TBLOCK_ABORT_PENDING:
			return "ABORT PEND";
		case TBLOCK_PREPARE:
			return "PREPARE";
		case TBLOCK_SUBBEGIN:
			return "SUB BEGIN";
		case TBLOCK_SUBINPROGRESS:
			return "SUB INPROGRS";
		case TBLOCK_SUBEND:
			return "SUB END";
		case TBLOCK_SUBABORT:
			return "SUB ABORT";
		case TBLOCK_SUBABORT_END:
			return "SUB ABORT END";
		case TBLOCK_SUBABORT_PENDING:
			return "SUB ABRT PEND";
		case TBLOCK_SUBRESTART:
			return "SUB RESTART";
		case TBLOCK_SUBABORT_RESTART:
			return "SUB AB RESTRT";
	}
	return "UNRECOGNIZED";
}

/*
 * TransStateAsString
 *		Debug support
 */
static const char *
TransStateAsString(TransState state)
{
	switch (state)
	{
		case TRANS_DEFAULT:
			return "DEFAULT";
		case TRANS_START:
			return "START";
		case TRANS_INPROGRESS:
			return "INPROGR";
		case TRANS_COMMIT:
			return "COMMIT";
		case TRANS_ABORT:
			return "ABORT";
		case TRANS_PREPARE:
			return "PREPARE";
	}
	return "UNRECOGNIZED";
}

/*
 * xactGetCommittedChildren
 *
 * Gets the list of committed children of the current transaction.	The return
 * value is the number of child transactions.  *children is set to point to a
 * palloc'd array of TransactionIds.  If there are no subxacts, *children is
 * set to NULL.
 */
int
xactGetCommittedChildren(TransactionId **ptr)
{
	TransactionState s = CurrentTransactionState;
	int			nchildren;
	TransactionId *children;
	ListCell   *p;

	nchildren = list_length(s->childXids);
	if (nchildren == 0)
	{
		*ptr = NULL;
		return 0;
	}

	children = (TransactionId *) palloc(nchildren * sizeof(TransactionId));
	*ptr = children;

	foreach(p, s->childXids)
	{
		TransactionId child = lfirst_xid(p);

		*children++ = child;
	}

	return nchildren;
}

/*
 *	XLOG support routines
 */

static void
xact_redo_commit(xl_xact_commit *xlrec, TransactionId xid)
{
	TransactionId *sub_xids;
	TransactionId max_xid;
	int			i;

	TransactionIdCommit(xid);

	/* Mark committed subtransactions as committed */
	sub_xids = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
	TransactionIdCommitTree(xlrec->nsubxacts, sub_xids);

	/* Make sure nextXid is beyond any XID mentioned in the record */
	max_xid = xid;
	for (i = 0; i < xlrec->nsubxacts; i++)
	{
		if (TransactionIdPrecedes(max_xid, sub_xids[i]))
			max_xid = sub_xids[i];
	}
	if (TransactionIdFollowsOrEquals(max_xid,
									 ShmemVariableCache->nextXid))
	{
		ShmemVariableCache->nextXid = max_xid;
		TransactionIdAdvance(ShmemVariableCache->nextXid);
	}

	/* Make sure files supposed to be dropped are dropped */
	for (i = 0; i < xlrec->nrels; i++)
	{
		XLogDropRelation(xlrec->xnodes[i]);
		smgrdounlink(smgropen(xlrec->xnodes[i]), false, true);
	}
}

static void
xact_redo_abort(xl_xact_abort *xlrec, TransactionId xid)
{
	TransactionId *sub_xids;
	TransactionId max_xid;
	int			i;

	TransactionIdAbort(xid);

	/* Mark subtransactions as aborted */
	sub_xids = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
	TransactionIdAbortTree(xlrec->nsubxacts, sub_xids);

	/* Make sure nextXid is beyond any XID mentioned in the record */
	max_xid = xid;
	for (i = 0; i < xlrec->nsubxacts; i++)
	{
		if (TransactionIdPrecedes(max_xid, sub_xids[i]))
			max_xid = sub_xids[i];
	}
	if (TransactionIdFollowsOrEquals(max_xid,
									 ShmemVariableCache->nextXid))
	{
		ShmemVariableCache->nextXid = max_xid;
		TransactionIdAdvance(ShmemVariableCache->nextXid);
	}

	/* Make sure files supposed to be dropped are dropped */
	for (i = 0; i < xlrec->nrels; i++)
	{
		XLogDropRelation(xlrec->xnodes[i]);
		smgrdounlink(smgropen(xlrec->xnodes[i]), false, true);
	}
}

void
xact_redo(XLogRecPtr lsn, XLogRecord *record)
{
	uint8		info = record->xl_info & ~XLR_INFO_MASK;

	if (info == XLOG_XACT_COMMIT)
	{
		xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);

		xact_redo_commit(xlrec, record->xl_xid);
	}
	else if (info == XLOG_XACT_ABORT)
	{
		xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(record);

		xact_redo_abort(xlrec, record->xl_xid);
	}
	else if (info == XLOG_XACT_PREPARE)
	{
		/* the record contents are exactly the 2PC file */
		RecreateTwoPhaseFile(record->xl_xid,
							 XLogRecGetData(record), record->xl_len);
	}
	else if (info == XLOG_XACT_COMMIT_PREPARED)
	{
		xl_xact_commit_prepared *xlrec = (xl_xact_commit_prepared *) XLogRecGetData(record);

		xact_redo_commit(&xlrec->crec, xlrec->xid);
		RemoveTwoPhaseFile(xlrec->xid, false);
	}
	else if (info == XLOG_XACT_ABORT_PREPARED)
	{
		xl_xact_abort_prepared *xlrec = (xl_xact_abort_prepared *) XLogRecGetData(record);

		xact_redo_abort(&xlrec->arec, xlrec->xid);
		RemoveTwoPhaseFile(xlrec->xid, false);
	}
	else
		elog(PANIC, "xact_redo: unknown op code %u", info);
}

static void
xact_desc_commit(StringInfo buf, xl_xact_commit *xlrec)
{
	struct tm  *tm = localtime(&xlrec->xtime);
	int			i;

	appendStringInfo(buf, "%04u-%02u-%02u %02u:%02u:%02u",
					 tm->tm_year + 1900, tm->tm_mon + 1, tm->tm_mday,
					 tm->tm_hour, tm->tm_min, tm->tm_sec);
	if (xlrec->nrels > 0)
	{
		appendStringInfo(buf, "; rels:");
		for (i = 0; i < xlrec->nrels; i++)
		{
			RelFileNode rnode = xlrec->xnodes[i];

			appendStringInfo(buf, " %u/%u/%u",
							 rnode.spcNode, rnode.dbNode, rnode.relNode);
		}
	}
	if (xlrec->nsubxacts > 0)
	{
		TransactionId *xacts = (TransactionId *)
		&xlrec->xnodes[xlrec->nrels];

		appendStringInfo(buf, "; subxacts:");
		for (i = 0; i < xlrec->nsubxacts; i++)
			appendStringInfo(buf, " %u", xacts[i]);
	}
}

static void
xact_desc_abort(StringInfo buf, xl_xact_abort *xlrec)
{
	struct tm  *tm = localtime(&xlrec->xtime);
	int			i;

	appendStringInfo(buf, "%04u-%02u-%02u %02u:%02u:%02u",
					 tm->tm_year + 1900, tm->tm_mon + 1, tm->tm_mday,
					 tm->tm_hour, tm->tm_min, tm->tm_sec);
	if (xlrec->nrels > 0)
	{
		appendStringInfo(buf, "; rels:");
		for (i = 0; i < xlrec->nrels; i++)
		{
			RelFileNode rnode = xlrec->xnodes[i];

			appendStringInfo(buf, " %u/%u/%u",
							 rnode.spcNode, rnode.dbNode, rnode.relNode);
		}
	}
	if (xlrec->nsubxacts > 0)
	{
		TransactionId *xacts = (TransactionId *)
		&xlrec->xnodes[xlrec->nrels];

		appendStringInfo(buf, "; subxacts:");
		for (i = 0; i < xlrec->nsubxacts; i++)
			appendStringInfo(buf, " %u", xacts[i]);
	}
}

void
xact_desc(StringInfo buf, uint8 xl_info, char *rec)
{
	uint8		info = xl_info & ~XLR_INFO_MASK;

	if (info == XLOG_XACT_COMMIT)
	{
		xl_xact_commit *xlrec = (xl_xact_commit *) rec;

		appendStringInfo(buf, "commit: ");
		xact_desc_commit(buf, xlrec);
	}
	else if (info == XLOG_XACT_ABORT)
	{
		xl_xact_abort *xlrec = (xl_xact_abort *) rec;

		appendStringInfo(buf, "abort: ");
		xact_desc_abort(buf, xlrec);
	}
	else if (info == XLOG_XACT_PREPARE)
	{
		appendStringInfo(buf, "prepare");
	}
	else if (info == XLOG_XACT_COMMIT_PREPARED)
	{
		xl_xact_commit_prepared *xlrec = (xl_xact_commit_prepared *) rec;

		appendStringInfo(buf, "commit %u: ", xlrec->xid);
		xact_desc_commit(buf, &xlrec->crec);
	}
	else if (info == XLOG_XACT_ABORT_PREPARED)
	{
		xl_xact_abort_prepared *xlrec = (xl_xact_abort_prepared *) rec;

		appendStringInfo(buf, "abort %u: ", xlrec->xid);
		xact_desc_abort(buf, &xlrec->arec);
	}
	else
		appendStringInfo(buf, "UNKNOWN");
}