Avoid checkpoint between commit record and persistent post-commit.

The commit xlog record carries the information for objects which serves us for
crash-recovery till post-commit persistent object work is done, hence cannot
allow checkpoint in between. So, use inCommit flag to achieve the same. This
makes it consistent with FinishPreparedTransaction() as well.

Without the fix leaves out dangling persistent table entries and files on-disk
for following sequence:

- start transaction to drop a table
- `RecordTransactionCommit()`
- Checkpoint before `AtEOXact_smgr()`
- Crash/Recover

src/backend/access/transam/twophase.c

@@ -1324,8 +1324,6 @@ EndPrepare(GlobalTransaction gxact)
 	/* Add the prepared record to our global list */
 	add_recover_post_checkpoint_prepared_transactions_map_entry(xid, &gxact->prepare_begin_lsn, "EndPrepare");
 
-	MyProc->inCommit = true;
-
 	XLogFlush(gxact->prepare_lsn);
 
 	/*

src/backend/access/transam/xact.c

@@ -1038,15 +1038,14 @@ AtSubStart_ResourceOwner(void)
  *
  * Returns latest XID among xact and its children, or InvalidTransactionId
  * if the xact has no XID.	(We compute that here just because it's easier.)
- *
- * This is exported only to support an ugly hack in VACUUM FULL.
  */
-TransactionId
+static TransactionId
 RecordTransactionCommit(void)
 {
 	TransactionId xid;
 	bool		markXidCommitted;
 	TransactionId latestXid = InvalidTransactionId;
+	bool save_inCommit;
 	MIRRORED_LOCK_DECLARE;
 
 	int32						persistentCommitSerializeLen;
@@ -1164,6 +1163,7 @@ RecordTransactionCommit(void)
 		 * bit fuzzy, but it doesn't matter.
 		 */
 		START_CRIT_SECTION();
+		save_inCommit = MyProc->inCommit;
 		MyProc->inCommit = true;
 
 		MIRRORED_LOCK;
@@ -1370,7 +1370,7 @@ RecordTransactionCommit(void)
 	 */
 	if (markXidCommitted)
 	{
-		MyProc->inCommit = false;
+		MyProc->inCommit = save_inCommit;
 		END_CRIT_SECTION();
 
 		MIRRORED_UNLOCK;
@@ -3428,6 +3428,15 @@ CommitTransaction(void)
 		 * and FileRepResyncManager_InResyncTransition()
 		 */
 		MIRRORED_LOCK;
+		/*
+		 * Need to ensure the recording of the commit record and the
+		 * persistent post-commit work will be done either before or after a
+		 * checkpoint. The commit xlog record carries the information for
+		 * objects which serves us for crash-recovery till post-commit
+		 * persistent object work is done, hence cannot allow checkpoint in
+		 * between.
+		 */
+		MyProc->inCommit = true;
 	}
 
 	/* Prevent cancel/die interrupt while cleaning up */
@@ -3546,6 +3555,7 @@ CommitTransaction(void)
 	if (willHaveObjectsFromSmgr)
 	{
 		MIRRORED_UNLOCK;
+		MyProc->inCommit = false;
 	}
 	
 	AtEOXact_MultiXact();

src/include/access/xact.h

@@ -247,7 +247,6 @@ extern void UnregisterXactCallbackOnce(XactCallback callback, void *arg);
 extern void RegisterSubXactCallback(SubXactCallback callback, void *arg);
 extern void UnregisterSubXactCallback(SubXactCallback callback, void *arg);
 
-extern TransactionId RecordTransactionCommit(void);
 extern void RecordDistributedForgetCommitted(struct TMGXACT_LOG *gxact_log);
 extern bool RecordCrashTransactionAbortRecord(
 	TransactionId				xid,