Nested transactions. There is still much left to do, especially on the

performance front, but with feature freeze upon us I think it's time to
drive a stake in the ground and say that this will be in 7.5.

Alvaro Herrera, with some help from Tom Lane.

src/backend/storage/buffer/bufmgr.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.171 2004/06/18 06:13:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.172 2004/07/01 00:50:46 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -45,6 +45,7 @@
 #include "storage/bufpage.h"
 #include "storage/proc.h"
 #include "storage/smgr.h"
+#include "utils/memutils.h"
 #include "utils/relcache.h"
 #include "pgstat.h"
 
@@ -64,9 +65,13 @@ long		NDirectFileRead;	/* some I/O's are direct file access.
 								 * bypass bufmgr */
 long		NDirectFileWrite;	/* e.g., I/O in psort and hashjoin. */
 
+/* List of upper-level-transaction buffer refcount arrays */
+static List *upperRefCounts = NIL;
+
 
 static void PinBuffer(BufferDesc *buf);
 static void UnpinBuffer(BufferDesc *buf);
+static void BufferFixLeak(Buffer bufnum, int32 shouldBe, bool emitWarning);
 static void WaitIO(BufferDesc *buf);
 static void StartBufferIO(BufferDesc *buf, bool forInput);
 static void TerminateBufferIO(BufferDesc *buf, int err_flag);
@@ -826,30 +831,104 @@ AtEOXact_Buffers(bool isCommit)
 	for (i = 0; i < NBuffers; i++)
 	{
 		if (PrivateRefCount[i] != 0)
-		{
-			BufferDesc *buf = &(BufferDescriptors[i]);
-
-			if (isCommit)
-				elog(WARNING,
-					 "buffer refcount leak: [%03d] "
-					 "(rel=%u/%u/%u, blockNum=%u, flags=0x%x, refcount=%u %d)",
-					 i,
-					 buf->tag.rnode.spcNode, buf->tag.rnode.dbNode,
-					 buf->tag.rnode.relNode,
-					 buf->tag.blockNum, buf->flags,
-					 buf->refcount, PrivateRefCount[i]);
-
-			PrivateRefCount[i] = 1;		/* make sure we release shared pin */
-			LWLockAcquire(BufMgrLock, LW_EXCLUSIVE);
-			UnpinBuffer(buf);
-			LWLockRelease(BufMgrLock);
-			Assert(PrivateRefCount[i] == 0);
-		}
+			BufferFixLeak(i, 0, isCommit);
 	}
 
 	AtEOXact_LocalBuffers(isCommit);
 }
 
+/*
+ * During subtransaction start, save buffer reference counts.
+ */
+void
+AtSubStart_Buffers(void)
+{
+	int32		   *copyRefCounts;
+	Size			rcSize;
+	MemoryContext	old_cxt;
+
+	/* this is probably the active context already, but be safe */
+	old_cxt = MemoryContextSwitchTo(CurTransactionContext);
+
+	/*
+	 * We need to copy the current state of PrivateRefCount[].  In the typical
+	 * scenario, few if any of the entries will be nonzero, and we could save
+	 * space by storing only the nonzero ones.  However, copying the whole
+	 * thing is lots simpler and faster both here and in AtEOSubXact_Buffers,
+	 * so it seems best to waste the space.
+	 */
+	rcSize = NBuffers * sizeof(int32);
+	copyRefCounts = (int32 *) palloc(rcSize);
+	memcpy(copyRefCounts, PrivateRefCount, rcSize);
+
+	/* Attach to list */
+	upperRefCounts = lcons(copyRefCounts, upperRefCounts);
+
+	MemoryContextSwitchTo(old_cxt);
+}
+
+/*
+ * AtEOSubXact_Buffers
+ *
+ * At subtransaction end, we restore the saved counts.  If committing, we
+ * complain if the refcounts don't match; if aborting, just restore silently.
+ */
+void
+AtEOSubXact_Buffers(bool isCommit)
+{
+	int32	   *oldRefCounts;
+	int			i;
+
+	oldRefCounts = (int32 *) linitial(upperRefCounts);
+	upperRefCounts = list_delete_first(upperRefCounts);
+
+	for (i = 0; i < NBuffers; i++)
+	{
+		if (PrivateRefCount[i] != oldRefCounts[i])
+			BufferFixLeak(i, oldRefCounts[i], isCommit);
+	}
+
+	pfree(oldRefCounts);
+}
+
+/*
+ * Fix a buffer refcount leak.
+ *
+ * The caller does not hold the BufMgrLock.
+ */
+static void
+BufferFixLeak(Buffer bufnum, int32 shouldBe, bool emitWarning)
+{
+	BufferDesc	*buf = &(BufferDescriptors[bufnum]);
+
+	if (emitWarning)
+		elog(WARNING,
+			 "buffer refcount leak: [%03d] (rel=%u/%u/%u, blockNum=%u, flags=0x%x, refcount=%u %d, should be=%d)",
+			 bufnum,
+			 buf->tag.rnode.spcNode, buf->tag.rnode.dbNode,
+			 buf->tag.rnode.relNode,
+			 buf->tag.blockNum, buf->flags,
+			 buf->refcount, PrivateRefCount[bufnum], shouldBe);
+
+	/* If it's less, we're in a heap o' trouble */
+	if (PrivateRefCount[bufnum] <= shouldBe)
+		elog(FATAL, "buffer refcount was decreased by subtransaction");
+
+	if (shouldBe > 0)
+	{
+		/* We still keep the shared-memory pin */
+		PrivateRefCount[bufnum] = shouldBe;
+	}
+	else
+	{
+		PrivateRefCount[bufnum] = 1; /* make sure we release shared pin */
+		LWLockAcquire(BufMgrLock, LW_EXCLUSIVE);
+		UnpinBuffer(buf);
+		LWLockRelease(BufMgrLock);
+		Assert(PrivateRefCount[bufnum] == 0);
+	}
+}
+
 /*
  * FlushBufferPool
  *

src/backend/storage/ipc/ipci.c

@@ -8,16 +8,16 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.68 2004/05/29 22:48:20 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.69 2004/07/01 00:50:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
-
-#include "miscadmin.h"
 #include "access/clog.h"
+#include "access/subtrans.h"
 #include "access/xlog.h"
+#include "miscadmin.h"
 #include "postmaster/bgwriter.h"
 #include "storage/bufmgr.h"
 #include "storage/freespace.h"
@@ -70,6 +70,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate,
 		size += LockShmemSize(maxBackends);
 		size += XLOGShmemSize();
 		size += CLOGShmemSize();
+		size += SUBTRANSShmemSize();
 		size += LWLockShmemSize();
 		size += SInvalShmemSize(maxBackends);
 		size += FreeSpaceShmemSize();
@@ -133,6 +134,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate,
 	 */
 	XLOGShmemInit();
 	CLOGShmemInit();
+	SUBTRANSShmemInit();
 	InitBufferPool();
 
 	/*

src/backend/storage/ipc/sinval.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.64 2004/06/02 21:29:28 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.65 2004/07/01 00:50:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -16,6 +16,8 @@
 
 #include <signal.h>
 
+#include "access/subtrans.h"
+#include "access/transam.h"
 #include "commands/async.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
@@ -428,20 +430,40 @@ DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself)
 
 /*
  * TransactionIdIsInProgress -- is given transaction running by some backend
+ *
+ * There are three possibilities for finding a running transaction:
+ *
+ * 1. the given Xid is a main transaction Id.  We will find this out cheaply
+ * by looking at the PGPROC struct for each backend.
+ *
+ * 2. the given Xid is one of the cached subxact Xids in the PGPROC array.
+ * We can find this out cheaply too.
+ *
+ * 3. Search the SubTrans tree.  This is the slowest, but sadly it has to be
+ * done always if the other two failed.
+ *
+ * SInvalLock has to be held while we do 1 and 2.  If we save all the Xids
+ * while doing 1, we can release the SInvalLock while we do 3.  This buys back
+ * some concurrency (we can't retrieve the main Xids from PGPROC again anyway,
+ * see GetNewTransactionId)
  */
 bool
 TransactionIdIsInProgress(TransactionId xid)
 {
-	bool		result = false;
-	SISeg	   *segP = shmInvalBuffer;
-	ProcState  *stateP = segP->procState;
-	int			index;
+	bool			result = false;
+	SISeg		   *segP = shmInvalBuffer;
+	ProcState	   *stateP = segP->procState;
+	int				i;
+	int				nxids = 0;
+	TransactionId  *xids;
+
+	xids = (TransactionId *)palloc(sizeof(TransactionId) * segP->maxBackends);
 
 	LWLockAcquire(SInvalLock, LW_SHARED);
 
-	for (index = 0; index < segP->lastBackend; index++)
+	for (i = 0; i < segP->lastBackend; i++)
 	{
-		SHMEM_OFFSET pOffset = stateP[index].procStruct;
+		SHMEM_OFFSET pOffset = stateP[i].procStruct;
 
 		if (pOffset != INVALID_OFFSET)
 		{
@@ -450,16 +472,71 @@ TransactionIdIsInProgress(TransactionId xid)
 			/* Fetch xid just once - see GetNewTransactionId */
 			TransactionId pxid = proc->xid;
 
+			/*
+			 * check the main Xid (step 1 above)
+			 */
 			if (TransactionIdEquals(pxid, xid))
 			{
 				result = true;
 				break;
 			}
+
+			/*
+			 * save the main Xid for step 3.
+			 */
+			xids[nxids++] = pxid;
+
+#ifdef NOT_USED
+			FIXME -- waiting to save the Xids in PGPROC ...
+
+			/*
+			 * check the saved Xids array (step 2)
+			 */
+			for (j = 0; j < PGPROC_MAX_SAVED_XIDS; j++)
+			{
+				pxid = proc->savedxids[j];
+
+				if (!TransactionIdIsValid(pxids))
+					break;
+
+				if (TransactionIdEquals(pxid, xid))
+				{
+					result = true;
+					break;
+				}
+			}
+#endif
+
+			if (result)
+				break;
+
 		}
 	}
 
 	LWLockRelease(SInvalLock);
 
+	/*
+	 * Step 3: have to check pg_subtrans.  Use the saved Xids.
+	 *
+	 * XXX Could save the cached Xids too for further improvement.
+	 */
+	if (!result)
+	{
+		/* this is a potentially expensive call. */
+		xid = SubTransGetTopmostTransaction(xid);
+		
+		Assert(TransactionIdIsValid(xid));
+
+		/*
+		 * We don't care if it aborted, because if it did, we won't find
+		 * it in the array.
+		 */
+
+		for (i = 0; i < nxids; i++)
+			if (TransactionIdEquals(xids[i], xid))
+				return true;
+	}
+
 	return result;
 }
 
@@ -596,7 +673,7 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
 	 * This does open a possibility for avoiding repeated malloc/free:
 	 * since MaxBackends does not change at runtime, we can simply reuse
 	 * the previous xip array if any.  (This relies on the fact that all
-	 * calls pass static SnapshotData structs.)
+	 * callers pass static SnapshotData structs.)
 	 */
 	if (snapshot->xip == NULL)
 	{

src/backend/storage/lmgr/lmgr.c

@@ -8,13 +8,14 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.63 2004/05/28 05:13:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.64 2004/07/01 00:50:59 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
 
+#include "access/subtrans.h"
 #include "access/transam.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
@@ -333,19 +334,21 @@ XactLockTableInsert(TransactionId xid)
  *		XactLockTableWait
  *
  * Wait for the specified transaction to commit or abort.
+ * We actually wait on the topmost transaction of the transaction tree.
  */
 void
 XactLockTableWait(TransactionId xid)
 {
 	LOCKTAG		tag;
 	TransactionId myxid = GetCurrentTransactionId();
+	TransactionId waitXid = SubTransGetTopmostTransaction(xid);
 
-	Assert(!TransactionIdEquals(xid, myxid));
+	Assert(!SubTransXidsHaveCommonAncestor(waitXid, myxid));
 
 	MemSet(&tag, 0, sizeof(tag));
 	tag.relId = XactLockTableId;
 	tag.dbId = InvalidOid;
-	tag.objId.xid = xid;
+	tag.objId.xid = waitXid;
 
 	if (!LockAcquire(LockTableId, &tag, myxid,
 					 ShareLock, false))
@@ -355,8 +358,13 @@ XactLockTableWait(TransactionId xid)
 
 	/*
 	 * Transaction was committed/aborted/crashed - we have to update
-	 * pg_clog if transaction is still marked as running.
+	 * pg_clog if transaction is still marked as running.  If it's a
+	 * subtransaction, we can update the parent status too.
 	 */
-	if (!TransactionIdDidCommit(xid) && !TransactionIdDidAbort(xid))
-		TransactionIdAbort(xid);
+	if (!TransactionIdDidCommit(waitXid) && !TransactionIdDidAbort(waitXid))
+	{
+		TransactionIdAbort(waitXid);
+		if (waitXid != xid)
+			TransactionIdAbort(xid);
+	}
 }

src/backend/storage/lmgr/lock.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.133 2004/06/05 19:48:08 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.134 2004/07/01 00:50:59 tgl Exp $
  *
  * NOTES
  *	  Outside modules can create a lock table and acquire/release
@@ -23,7 +23,7 @@
  *	Interface:
  *
  *	LockAcquire(), LockRelease(), LockMethodTableInit(),
- *	LockMethodTableRename(), LockReleaseAll,
+ *	LockMethodTableRename(), LockReleaseAll(),
  *	LockCheckConflicts(), GrantLock()
  *
  *-------------------------------------------------------------------------
@@ -1129,19 +1129,25 @@ LockRelease(LOCKMETHODID lockmethodid, LOCKTAG *locktag,
 }
 
 /*
- * LockReleaseAll -- Release all locks in a process's lock list.
+ * LockReleaseAll -- Release all locks of the specified lock method that
+ *		are held by the specified process.
  *
- * Well, not really *all* locks.
+ * Well, not necessarily *all* locks.  The available behaviors are:
  *
- * If 'allxids' is TRUE, all locks of the specified lock method are
- * released, regardless of transaction affiliation.
+ * which == ReleaseAll: release all locks regardless of transaction
+ * affiliation.
  *
- * If 'allxids' is FALSE, all locks of the specified lock method and
- * specified XID are released.
+ * which == ReleaseAllExceptSession: release all locks with Xid != 0
+ * (zero is the Xid used for "session" locks).
+ *
+ * which == ReleaseGivenXids: release only locks whose Xids appear in
+ * the xids[] array (of length nxids).
+ *
+ * xids/nxids are ignored when which != ReleaseGivenXids.
  */
 bool
 LockReleaseAll(LOCKMETHODID lockmethodid, PGPROC *proc,
-			   bool allxids, TransactionId xid)
+			   LockReleaseWhich which, int nxids, TransactionId *xids)
 {
 	SHM_QUEUE  *procHolders = &(proc->procHolders);
 	PROCLOCK   *proclock;
@@ -1190,8 +1196,25 @@ LockReleaseAll(LOCKMETHODID lockmethodid, PGPROC *proc,
 		if (LOCK_LOCKMETHOD(*lock) != lockmethodid)
 			goto next_item;
 
-		/* If not allxids, ignore items that are of the wrong xid */
-		if (!allxids && !TransactionIdEquals(xid, proclock->tag.xid))
+		if (which == ReleaseGivenXids)
+		{
+			/* Ignore locks with an Xid not in the list */
+			bool release = false;
+
+			for (i = 0; i < nxids; i++)
+			{
+				if (TransactionIdEquals(proclock->tag.xid, xids[i]))
+				{
+					release = true;
+					break;
+				}
+			}
+			if (!release)
+				goto next_item;
+		}
+		/* Ignore locks with Xid=0 unless we are asked to release All locks */
+		else if (TransactionIdEquals(proclock->tag.xid, InvalidTransactionId)
+				 && which != ReleaseAll)
 			goto next_item;
 
 		PROCLOCK_PRINT("LockReleaseAll", proclock);

src/backend/storage/lmgr/lwlock.c

@@ -15,13 +15,14 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lwlock.c,v 1.20 2004/06/11 16:43:24 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lwlock.c,v 1.21 2004/07/01 00:50:59 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
 #include "access/clog.h"
+#include "access/subtrans.h"
 #include "storage/lwlock.h"
 #include "storage/proc.h"
 #include "storage/spin.h"
@@ -111,6 +112,9 @@ NumLWLocks(void)
 	/* clog.c needs one per CLOG buffer + one control lock */
 	numLocks += NUM_CLOG_BUFFERS + 1;
 
+	/* subtrans.c needs one per SubTrans buffer + one control lock */
+	numLocks += NUM_SUBTRANS_BUFFERS + 1;
+
 	/* Perhaps create a few more for use by user-defined modules? */
 
 	return numLocks;

src/backend/storage/lmgr/proc.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.148 2004/05/29 22:48:20 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.149 2004/07/01 00:50:59 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -380,26 +380,34 @@ LockWaitCancel(void)
 
 /*
  * ProcReleaseLocks() -- release locks associated with current transaction
- *			at transaction commit or abort
+ *			at main transaction and subtransaction commit or abort
  *
- * At commit, we release only locks tagged with the current transaction's XID,
- * leaving those marked with XID 0 (ie, session locks) undisturbed.  At abort,
- * we release all locks including XID 0, because we need to clean up after
- * a failure.  This logic will need extension if we ever support nested
- * transactions.
+ * The options for which locks to release are the same as for the underlying
+ * LockReleaseAll() function.
  *
- * Note that user locks are not released in either case.
+ * Notes:
+ *
+ * At main transaction commit, we release all locks except session locks.
+ * At main transaction abort, we release all locks including session locks;
+ * this lets us clean up after a VACUUM FULL failure.
+ *
+ * At subtransaction commit, we don't release any locks (so this func is not
+ * called at all); we will defer the releasing to the parent transaction.
+ * At subtransaction abort, we release all locks held by the subtransaction;
+ * this is implemented by passing in the Xids of the failed subxact and its
+ * children in the xids[] array.
+ *
+ * Note that user locks are not released in any case.
  */
 void
-ProcReleaseLocks(bool isCommit)
+ProcReleaseLocks(LockReleaseWhich which, int nxids, TransactionId *xids)
 {
 	if (!MyProc)
 		return;
 	/* If waiting, get off wait queue (should only be needed after error) */
 	LockWaitCancel();
 	/* Release locks */
-	LockReleaseAll(DEFAULT_LOCKMETHOD, MyProc,
-				   !isCommit, GetCurrentTransactionId());
+	LockReleaseAll(DEFAULT_LOCKMETHOD, MyProc, which, nxids, xids);
 }
 
 
@@ -432,11 +440,11 @@ ProcKill(int code, Datum arg)
 	LockWaitCancel();
 
 	/* Remove from the standard lock table */
-	LockReleaseAll(DEFAULT_LOCKMETHOD, MyProc, true, InvalidTransactionId);
+	LockReleaseAll(DEFAULT_LOCKMETHOD, MyProc, ReleaseAll, 0, NULL);
 
 #ifdef USER_LOCKS
 	/* Remove from the user lock table */
-	LockReleaseAll(USER_LOCKMETHOD, MyProc, true, InvalidTransactionId);
+	LockReleaseAll(USER_LOCKMETHOD, MyProc, ReleaseAll, 0, NULL);
 #endif
 
 	SpinLockAcquire(ProcStructLock);

src/backend/storage/smgr/smgr.c

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.74 2004/06/18 06:13:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.75 2004/07/01 00:51:07 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -80,9 +80,10 @@ static HTAB *SMgrRelationHash = NULL;
  * executed immediately, but is just entered in the list.  When and if
  * the transaction commits, we can delete the physical file.
  *
- * NOTE: the list is kept in TopMemoryContext to be sure it won't disappear
- * unbetimes.  It'd probably be OK to keep it in TopTransactionContext,
- * but I'm being paranoid.
+ * The list is kept in CurTransactionContext.  In subtransactions, each
+ * subtransaction has its own list in its own CurTransactionContext, but
+ * successful subtransactions attach their lists to their parent's list.
+ * Failed subtransactions can immediately execute the abort-time actions.
  */
 
 typedef struct PendingRelDelete
@@ -91,10 +92,11 @@ typedef struct PendingRelDelete
 	int			which;			/* which storage manager? */
 	bool		isTemp;			/* is it a temporary relation? */
 	bool		atCommit;		/* T=delete at commit; F=delete at abort */
-	struct PendingRelDelete *next;		/* linked-list link */
 } PendingRelDelete;
 
-static PendingRelDelete *pendingDeletes = NULL; /* head of linked list */
+static List *pendingDeletes = NIL;		/* head of linked list */
+
+static List *upperPendingDeletes = NIL; /* list of upper-xact lists */
 
 
 /*
@@ -305,6 +307,7 @@ smgrcreate(SMgrRelation reln, bool isTemp, bool isRedo)
 	XLogRecData		rdata;
 	xl_smgr_create	xlrec;
 	PendingRelDelete *pending;
+	MemoryContext	old_cxt;
 
 	if (! (*(smgrsw[reln->smgr_which].smgr_create)) (reln, isRedo))
 		ereport(ERROR,
@@ -332,14 +335,17 @@ smgrcreate(SMgrRelation reln, bool isTemp, bool isRedo)
 	lsn = XLogInsert(RM_SMGR_ID, XLOG_SMGR_CREATE | XLOG_NO_TRAN, &rdata);
 
 	/* Add the relation to the list of stuff to delete at abort */
-	pending = (PendingRelDelete *)
-		MemoryContextAlloc(TopMemoryContext, sizeof(PendingRelDelete));
+	old_cxt = MemoryContextSwitchTo(CurTransactionContext);
+
+	pending = (PendingRelDelete *) palloc(sizeof(PendingRelDelete));
 	pending->relnode = reln->smgr_rnode;
 	pending->which = reln->smgr_which;
 	pending->isTemp = isTemp;
 	pending->atCommit = false;	/* delete if abort */
-	pending->next = pendingDeletes;
-	pendingDeletes = pending;
+
+	pendingDeletes = lcons(pending, pendingDeletes);
+
+	MemoryContextSwitchTo(old_cxt);
 }
 
 /*
@@ -354,16 +360,20 @@ void
 smgrscheduleunlink(SMgrRelation reln, bool isTemp)
 {
 	PendingRelDelete *pending;
+	MemoryContext	 old_cxt;
 
 	/* Add the relation to the list of stuff to delete at commit */
-	pending = (PendingRelDelete *)
-		MemoryContextAlloc(TopMemoryContext, sizeof(PendingRelDelete));
+	old_cxt = MemoryContextSwitchTo(CurTransactionContext);
+
+	pending = (PendingRelDelete *) palloc(sizeof(PendingRelDelete));
 	pending->relnode = reln->smgr_rnode;
 	pending->which = reln->smgr_which;
 	pending->isTemp = isTemp;
 	pending->atCommit = true;	/* delete if commit */
-	pending->next = pendingDeletes;
-	pendingDeletes = pending;
+
+	pendingDeletes = lcons(pending, pendingDeletes);
+
+	MemoryContextSwitchTo(old_cxt);
 
 	/*
 	 * NOTE: if the relation was created in this transaction, it will now
@@ -627,18 +637,21 @@ smgrimmedsync(SMgrRelation reln)
 void
 smgrDoPendingDeletes(bool isCommit)
 {
-	while (pendingDeletes != NULL)
-	{
-		PendingRelDelete *pending = pendingDeletes;
+	ListCell *p;
+
+	foreach(p, pendingDeletes)
+	{
+		PendingRelDelete *pending = lfirst(p);
 
-		pendingDeletes = pending->next;
 		if (pending->atCommit == isCommit)
 			smgr_internal_unlink(pending->relnode,
 								 pending->which,
 								 pending->isTemp,
 								 false);
-		pfree(pending);
 	}
+
+	/* We needn't free the cells since they are in CurTransactionContext */
+	pendingDeletes = NIL;
 }
 
 /*
@@ -647,17 +660,22 @@ smgrDoPendingDeletes(bool isCommit)
  * The return value is the number of relations scheduled for termination.
  * *ptr is set to point to a freshly-palloc'd array of RelFileNodes.
  * If there are no relations to be deleted, *ptr is set to NULL.
+ *
+ * Note that the list does not include anything scheduled for termination
+ * by upper-level transactions.
  */
 int
 smgrGetPendingDeletes(bool forCommit, RelFileNode **ptr)
 {
 	int			nrels;
 	RelFileNode *rptr;
-	PendingRelDelete *pending;
+	ListCell	*p;
 
 	nrels = 0;
-	for (pending = pendingDeletes; pending != NULL; pending = pending->next)
+	foreach(p, pendingDeletes)
 	{
+		PendingRelDelete *pending = lfirst(p);
+
 		if (pending->atCommit == forCommit)
 			nrels++;
 	}
@@ -668,14 +686,69 @@ smgrGetPendingDeletes(bool forCommit, RelFileNode **ptr)
 	}
 	rptr = (RelFileNode *) palloc(nrels * sizeof(RelFileNode));
 	*ptr = rptr;
-	for (pending = pendingDeletes; pending != NULL; pending = pending->next)
+	foreach(p, pendingDeletes)
 	{
+		PendingRelDelete *pending = lfirst(p);
+
 		if (pending->atCommit == forCommit)
 			*rptr++ = pending->relnode;
 	}
 	return nrels;
 }
 
+/*
+ * AtSubStart_smgr() --- Take care of subtransaction start.
+ *
+ * Push empty state for the new subtransaction.
+ */
+void
+AtSubStart_smgr(void)
+{
+	MemoryContext	old_cxt;
+
+	/* Keep the list-of-lists in TopTransactionContext for simplicity */
+	old_cxt = MemoryContextSwitchTo(TopTransactionContext);
+
+	upperPendingDeletes = lcons(pendingDeletes, upperPendingDeletes);
+
+	pendingDeletes = NIL;
+
+	MemoryContextSwitchTo(old_cxt);
+}
+
+/*
+ * AtSubCommit_smgr() --- Take care of subtransaction commit.
+ *
+ * Reassign all items in the pending deletes list to the parent transaction.
+ */
+void
+AtSubCommit_smgr(void)
+{
+	List	*parentPendingDeletes;
+
+	parentPendingDeletes = (List *) linitial(upperPendingDeletes);
+	upperPendingDeletes = list_delete_first(upperPendingDeletes);
+
+	pendingDeletes = list_concat(parentPendingDeletes, pendingDeletes);
+}
+
+/*
+ * AtSubAbort_smgr() --- Take care of subtransaction abort.
+ *
+ * Delete created relations and forget about deleted relations.
+ * We can execute these operations immediately because we know this
+ * subtransaction will not commit.
+ */
+void
+AtSubAbort_smgr(void)
+{
+	smgrDoPendingDeletes(false);
+
+	/* Must pop the stack, too */
+	pendingDeletes = (List *) linitial(upperPendingDeletes);
+	upperPendingDeletes = list_delete_first(upperPendingDeletes);
+}
+
 /*
  *	smgrcommit() -- Prepare to commit changes made during the current
  *					transaction.