rewriteHandler.c

/*-------------------------------------------------------------------------
 *
 * rewriteHandler.c--
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.5 1997/09/08 02:28:17 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "miscadmin.h"
#include "utils/palloc.h"
#include "utils/elog.h"
#include "utils/rel.h"
#include "nodes/pg_list.h"
#include "nodes/primnodes.h"

#include "parser/parsetree.h"	/* for parsetree manipulation */
#include "nodes/parsenodes.h"

#include "rewrite/rewriteSupport.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/locks.h"

#include "commands/creatinh.h"
#include "access/heapam.h"

static void
ApplyRetrieveRule(Query * parsetree, RewriteRule * rule,
				  int rt_index, int relation_level, int *modified);
static List *
fireRules(Query * parsetree, int rt_index, CmdType event,
		  bool * instead_flag, List * locks, List ** qual_products);
static List *deepRewriteQuery(Query * parsetree);

/*
 * gatherRewriteMeta -
 *	  Gather meta information about parsetree, and rule. Fix rule body
 *	  and qualifier so that they can be mixed with the parsetree and
 *	  maintain semantic validity
 */
static RewriteInfo *
gatherRewriteMeta(Query * parsetree,
				  Query * rule_action,
				  Node * rule_qual,
				  int rt_index,
				  CmdType event,
				  bool * instead_flag)
{
	RewriteInfo *info;
	int			rt_length;
	int			result_reln;

	info = (RewriteInfo *) palloc(sizeof(RewriteInfo));
	info->rt_index = rt_index;
	info->event = event;
	info->instead_flag = *instead_flag;
	info->rule_action = (Query *) copyObject(rule_action);
	info->rule_qual = (Node *) copyObject(rule_qual);
	if (info->rule_action == NULL)
		info->nothing = TRUE;
	else
	{
		info->nothing = FALSE;
		info->action = info->rule_action->commandType;
		info->current_varno = rt_index;
		info->rt = parsetree->rtable;
		rt_length = length(info->rt);
		info->rt = append(info->rt, info->rule_action->rtable);

		info->new_varno = PRS2_NEW_VARNO + rt_length;
		OffsetVarNodes(info->rule_action->qual, rt_length);
		OffsetVarNodes((Node *) info->rule_action->targetList, rt_length);
		OffsetVarNodes(info->rule_qual, rt_length);
		ChangeVarNodes((Node *) info->rule_action->qual,
					   PRS2_CURRENT_VARNO + rt_length, rt_index);
		ChangeVarNodes((Node *) info->rule_action->targetList,
					   PRS2_CURRENT_VARNO + rt_length, rt_index);
		ChangeVarNodes(info->rule_qual,
					   PRS2_CURRENT_VARNO + rt_length, rt_index);

		/*
		 * bug here about replace CURRENT  -- sort of replace current is
		 * deprecated now so this code shouldn't really need to be so
		 * clutzy but.....
		 */
		if (info->action != CMD_SELECT)
		{						/* i.e update XXXXX */
			int			new_result_reln = 0;

			result_reln = info->rule_action->resultRelation;
			switch (result_reln)
			{
				case PRS2_CURRENT_VARNO:
					new_result_reln = rt_index;
					break;
				case PRS2_NEW_VARNO:	/* XXX */
				default:
					new_result_reln = result_reln + rt_length;
					break;
			}
			info->rule_action->resultRelation = new_result_reln;
		}
	}
	return info;
}

static List *
OptimizeRIRRules(List * locks)
{
	List	   *attr_level = NIL,
			   *i;
	List	   *relation_level = NIL;

	foreach(i, locks)
	{
		RewriteRule *rule_lock = lfirst(i);

		if (rule_lock->attrno == -1)
			relation_level = lappend(relation_level, rule_lock);
		else
			attr_level = lappend(attr_level, rule_lock);
	}
	return nconc(relation_level, attr_level);
}

/*
 * idea is to put instead rules before regular rules so that
 * excess semantically queasy queries aren't processed
 */
static List *
orderRules(List * locks)
{
	List	   *regular = NIL,
			   *i;
	List	   *instead_rules = NIL;

	foreach(i, locks)
	{
		RewriteRule *rule_lock = (RewriteRule *) lfirst(i);

		if (rule_lock->isInstead)
			instead_rules = lappend(instead_rules, rule_lock);
		else
			regular = lappend(regular, rule_lock);
	}
	return nconc(regular, instead_rules);
}

static int
AllRetrieve(List * actions)
{
	List	   *n;

	foreach(n, actions)
	{
		Query	   *pt = lfirst(n);

		/*
		 * in the old postgres code, we check whether command_type is a
		 * consp of '('*'.commandType). but we've never supported
		 * transitive closures. Hence removed	 - ay 10/94.
		 */
		if (pt->commandType != CMD_SELECT)
			return false;
	}
	return true;
}

static List *
FireRetrieveRulesAtQuery(Query * parsetree,
						 int rt_index,
						 Relation relation,
						 bool * instead_flag,
						 int rule_flag)
{
	List	   *i,
			   *locks;
	RuleLock   *rt_entry_locks = NULL;
	List	   *work = NIL;

	if ((rt_entry_locks = relation->rd_rules) == NULL)
		return NIL;

	locks = matchLocks(CMD_SELECT, rt_entry_locks, rt_index, parsetree);

	/* find all retrieve instead */
	foreach(i, locks)
	{
		RewriteRule *rule_lock = (RewriteRule *) lfirst(i);

		if (!rule_lock->isInstead)
			continue;
		work = lappend(work, rule_lock);
	}
	if (work != NIL)
	{
		work = OptimizeRIRRules(locks);
		foreach(i, work)
		{
			RewriteRule *rule_lock = lfirst(i);
			int			relation_level;
			int			modified = FALSE;

			relation_level = (rule_lock->attrno == -1);
			if (rule_lock->actions == NIL)
			{
				*instead_flag = TRUE;
				return NIL;
			}
			if (!rule_flag &&
				length(rule_lock->actions) >= 2 &&
				AllRetrieve(rule_lock->actions))
			{
				*instead_flag = TRUE;
				return rule_lock->actions;
			}
			ApplyRetrieveRule(parsetree, rule_lock, rt_index, relation_level,
							  &modified);
			if (modified)
			{
				*instead_flag = TRUE;
				FixResdomTypes(parsetree->targetList);
				return lcons(parsetree, NIL);
			}
		}
	}
	return NIL;
}


/* Idea is like this:
 *
 * retrieve-instead-retrieve rules have different semantics than update nodes
 * Separate RIR rules from others.	Pass others to FireRules.
 * Order RIR rules and process.
 *
 * side effect: parsetree's rtable field might be changed
 */
static void
ApplyRetrieveRule(Query * parsetree,
				  RewriteRule * rule,
				  int rt_index,
				  int relation_level,
				  int *modified)
{
	Query	   *rule_action = NULL;
	Node	   *rule_qual;
	List	   *rtable,
			   *rt;
	int			nothing,
				rt_length;
	int			badsql = FALSE;

	rule_qual = rule->qual;
	if (rule->actions)
	{
		if (length(rule->actions) > 1)	/* ??? because we don't handle
										 * rules with more than one
										 * action? -ay */
			return;
		rule_action = copyObject(lfirst(rule->actions));
		nothing = FALSE;
	}
	else
	{
		nothing = TRUE;
	}

	rtable = copyObject(parsetree->rtable);
	foreach(rt, rtable)
	{
		RangeTblEntry *rte = lfirst(rt);

		/*
		 * this is to prevent add_missing_vars_to_base_rels() from adding
		 * a bogus entry to the new target list.
		 */
		rte->inFromCl = false;
	}
	rt_length = length(rtable);
	rtable = nconc(rtable, copyObject(rule_action->rtable));
	parsetree->rtable = rtable;

	rule_action->rtable = rtable;
	OffsetVarNodes(rule_action->qual, rt_length);
	OffsetVarNodes((Node *) rule_action->targetList, rt_length);
	OffsetVarNodes(rule_qual, rt_length);
	ChangeVarNodes(rule_action->qual,
				   PRS2_CURRENT_VARNO + rt_length, rt_index);
	ChangeVarNodes((Node *) rule_action->targetList,
				   PRS2_CURRENT_VARNO + rt_length, rt_index);
	ChangeVarNodes(rule_qual, PRS2_CURRENT_VARNO + rt_length, rt_index);
	if (relation_level)
	{
		HandleViewRule(parsetree, rtable, rule_action->targetList, rt_index,
					   modified);
	}
	else
	{
		HandleRIRAttributeRule(parsetree, rtable, rule_action->targetList,
							   rt_index, rule->attrno, modified, &badsql);
	}
	if (*modified && !badsql)
		AddQual(parsetree, rule_action->qual);
}

static List *
ProcessRetrieveQuery(Query * parsetree,
					 List * rtable,
					 bool * instead_flag,
					 bool rule)
{
	List	   *rt;
	List	   *product_queries = NIL;
	int			rt_index = 0;

	foreach(rt, rtable)
	{
		RangeTblEntry *rt_entry = lfirst(rt);
		Relation	rt_entry_relation = NULL;
		List	   *result = NIL;

		rt_index++;
		rt_entry_relation = heap_openr(rt_entry->relname);

		if (rt_entry_relation->rd_rules != NULL)
		{
			result =
				FireRetrieveRulesAtQuery(parsetree,
										 rt_index,
										 rt_entry_relation,
										 instead_flag,
										 rule);
		}
		heap_close(rt_entry_relation);
		if (*instead_flag)
			return result;
	}
	if (rule)
		return NIL;

	foreach(rt, rtable)
	{
		RangeTblEntry *rt_entry = lfirst(rt);
		Relation	rt_entry_relation = NULL;
		RuleLock   *rt_entry_locks = NULL;
		List	   *result = NIL;
		List	   *locks = NIL;
		List	   *dummy_products;

		rt_index++;
		rt_entry_relation = heap_openr(rt_entry->relname);
		rt_entry_locks = rt_entry_relation->rd_rules;
		heap_close(rt_entry_relation);

		if (rt_entry_locks)
		{
			locks =
				matchLocks(CMD_SELECT, rt_entry_locks, rt_index, parsetree);
		}
		if (locks != NIL)
		{
			result = fireRules(parsetree, rt_index, CMD_SELECT,
							   instead_flag, locks, &dummy_products);
			if (*instead_flag)
				return lappend(NIL, result);
			if (result != NIL)
				product_queries = nconc(product_queries, result);
		}
	}
	return product_queries;
}

static Query *
CopyAndAddQual(Query * parsetree,
			   List * actions,
			   Node * rule_qual,
			   int rt_index,
			   CmdType event)
{
	Query	   *new_tree = (Query *) copyObject(parsetree);
	Node	   *new_qual = NULL;
	Query	   *rule_action = NULL;

	if (actions)
		rule_action = lfirst(actions);
	if (rule_qual != NULL)
		new_qual = (Node *) copyObject(rule_qual);
	if (rule_action != NULL)
	{
		List	   *rtable;
		int			rt_length;

		rtable = new_tree->rtable;
		rt_length = length(rtable);
		rtable = append(rtable, listCopy(rule_action->rtable));
		new_tree->rtable = rtable;
		OffsetVarNodes(new_qual, rt_length);
		ChangeVarNodes(new_qual, PRS2_CURRENT_VARNO + rt_length, rt_index);
	}
	/* XXX -- where current doesn't work for instead nothing.... yet */
	AddNotQual(new_tree, new_qual);

	return new_tree;
}


/*
 *	fireRules -
 *	   Iterate through rule locks applying rules.  After an instead rule
 *	   rule has been applied, return just new parsetree and let RewriteQuery
 *	   start the process all over again.  The locks are reordered to maintain
 *	   sensible semantics.	remember: reality is for dead birds -- glass
 *
 */
static List *
fireRules(Query * parsetree,
		  int rt_index,
		  CmdType event,
		  bool * instead_flag,
		  List * locks,
		  List ** qual_products)
{
	RewriteInfo *info;
	List	   *results = NIL;
	List	   *i;

	/* choose rule to fire from list of rules */
	if (locks == NIL)
	{
		ProcessRetrieveQuery(parsetree,
							 parsetree->rtable,
							 instead_flag, TRUE);
		if (*instead_flag)
			return lappend(NIL, parsetree);
		else
			return NIL;
	}

	locks = orderRules(locks);	/* instead rules first */
	foreach(i, locks)
	{
		RewriteRule *rule_lock = (RewriteRule *) lfirst(i);
		Node	   *qual,
				   *event_qual;
		List	   *actions;
		List	   *r;
		bool		orig_instead_flag = *instead_flag;

		/* multiple rule action time */
		*instead_flag = rule_lock->isInstead;
		event_qual = rule_lock->qual;
		actions = rule_lock->actions;
		if (event_qual != NULL && *instead_flag)
			*qual_products =
				lappend(*qual_products,
						CopyAndAddQual(parsetree, actions, event_qual,
									   rt_index, event));
		foreach(r, actions)
		{
			Query	   *rule_action = lfirst(r);
			Node	   *rule_qual = copyObject(event_qual);

			/*--------------------------------------------------
			 * Step 1:
			 *	  Rewrite current.attribute or current to tuple variable
			 *	  this appears to be done in parser?
			 *--------------------------------------------------
			 */
			info = gatherRewriteMeta(parsetree, rule_action, rule_qual,
									 rt_index, event, instead_flag);

			/* handle escapable cases, or those handled by other code */
			if (info->nothing)
			{
				if (*instead_flag)
					return NIL;
				else
					continue;
			}

			if (info->action == info->event &&
				info->event == CMD_SELECT)
				continue;

			/*
			 * Event Qualification forces copying of parsetree --- XXX and
			 * splitting into two queries one w/rule_qual, one w/NOT
			 * rule_qual. Also add user query qual onto rule action
			 */
			qual = parsetree->qual;
			AddQual(info->rule_action, qual);

			if (info->rule_qual != NULL)
				AddQual(info->rule_action, info->rule_qual);

			/*--------------------------------------------------
			 * Step 2:
			 *	  Rewrite new.attribute w/ right hand side of target-list
			 *	  entry for appropriate field name in insert/update
			 *--------------------------------------------------
			 */
			if ((info->event == CMD_INSERT) || (info->event == CMD_UPDATE))
			{
				FixNew(info, parsetree);
			}

			/*--------------------------------------------------
			 * Step 3:
			 *	  rewriting due to retrieve rules
			 *--------------------------------------------------
			 */
			info->rule_action->rtable = info->rt;
			ProcessRetrieveQuery(info->rule_action, info->rt,
								 &orig_instead_flag, TRUE);

			/*--------------------------------------------------
			 * Step 4
			 *	  Simplify? hey, no algorithm for simplification... let
			 *	  the planner do it.
			 *--------------------------------------------------
			 */
			results = lappend(results, info->rule_action);

			pfree(info);
		}
		if (*instead_flag)
			break;
	}
	return results;
}

static List *
RewriteQuery(Query * parsetree, bool * instead_flag, List ** qual_products)
{
	CmdType		event;
	List	   *product_queries = NIL;
	int			result_relation = 0;

	Assert(parsetree != NULL);

	event = parsetree->commandType;

	if (event == CMD_UTILITY)
		return NIL;

	/*
	 * only for a delete may the targetlist be NULL
	 */
	if (event != CMD_DELETE)
	{
		Assert(parsetree->targetList != NULL);
	}

	result_relation = parsetree->resultRelation;

	if (event != CMD_SELECT)
	{

		/*
		 * the statement is an update, insert or delete
		 */
		RangeTblEntry *rt_entry;
		Relation	rt_entry_relation = NULL;
		RuleLock   *rt_entry_locks = NULL;

		rt_entry = rt_fetch(result_relation, parsetree->rtable);
		rt_entry_relation = heap_openr(rt_entry->relname);
		rt_entry_locks = rt_entry_relation->rd_rules;
		heap_close(rt_entry_relation);

		if (rt_entry_locks != NULL)
		{
			List	   *locks =
			matchLocks(event, rt_entry_locks, result_relation, parsetree);

			product_queries =
				fireRules(parsetree,
						  result_relation,
						  event,
						  instead_flag,
						  locks,
						  qual_products);
		}
		return product_queries;
	}
	else
	{

		/*
		 * the statement is a select
		 */
		Query	   *other;

		other = copyObject(parsetree);	/* ApplyRetrieveRule changes the
										 * range table */
		return
			ProcessRetrieveQuery(other, parsetree->rtable,
								 instead_flag, FALSE);
	}
}

/*
 * to avoid infinite recursion, we restrict the number of times a query
 * can be rewritten. Detecting cycles is left for the reader as an excercise.
 */
#ifndef REWRITE_INVOKE_MAX
#define REWRITE_INVOKE_MAX		10
#endif

static int	numQueryRewriteInvoked = 0;

/*
 * QueryRewrite -
 *	  rewrite one query via QueryRewrite system, possibly returning 0, or many
 *	  queries
 */
List	   *
QueryRewrite(Query * parsetree)
{
	numQueryRewriteInvoked = 0;

	/*
	 * take a deep breath and apply all the rewrite rules - ay
	 */
	return deepRewriteQuery(parsetree);
}

/*
 * deepRewriteQuery -
 *	  rewrites the query and apply the rules again on the queries rewritten
 */
static List *
deepRewriteQuery(Query * parsetree)
{
	List	   *n;
	List	   *rewritten = NIL;
	List	   *result = NIL;
	bool		instead;
	List	   *qual_products = NIL;

	if (++numQueryRewriteInvoked > REWRITE_INVOKE_MAX)
	{
		elog(WARN, "query rewritten %d times, may contain cycles",
			 numQueryRewriteInvoked - 1);
	}

	instead = FALSE;
	result = RewriteQuery(parsetree, &instead, &qual_products);
	if (!instead)
		rewritten = lcons(parsetree, NIL);

	foreach(n, result)
	{
		Query	   *pt = lfirst(n);
		List	   *newstuff = NIL;

		newstuff = deepRewriteQuery(pt);
		if (newstuff != NIL)
			rewritten = nconc(rewritten, newstuff);
	}
	if (qual_products != NIL)
		rewritten = nconc(rewritten, qual_products);

	return rewritten;
}