Restructure subtransaction handling to reduce resource consumption,

as per recent discussions.  Invent SubTransactionIds that are managed like
CommandIds (ie, counter is reset at start of each top transaction), and
use these instead of TransactionIds to keep track of subtransaction status
in those modules that need it.  This means that a subtransaction does not
need an XID unless it actually inserts/modifies rows in the database.
Accordingly, don't assign it an XID nor take a lock on the XID until it
tries to do that.  This saves a lot of overhead for subtransactions that
are only used for error recovery (eg plpgsql exceptions).  Also, arrange
to release a subtransaction's XID lock as soon as the subtransaction
exits, in both the commit and abort cases.  This avoids holding many
unique locks after a long series of subtransactions.  The price is some
additional overhead in XactLockTableWait, but that seems acceptable.
Finally, restructure the state machine in xact.c to have a more orthogonal
set of states for subtransactions.

3 files changed, 834 insertions, 621 deletions

diff --git a/src/backend/access/transam/README b/src/backend/access/transam/README
index deb6a12f8ed..a11f5707c73 100644
--- a/src/backend/access/transam/README
+++ b/src/backend/access/transam/README
@@ -1,4 +1,4 @@
-$PostgreSQL: pgsql/src/backend/access/transam/README,v 1.1 2004/08/01 20:57:59 tgl Exp $
+$PostgreSQL: pgsql/src/backend/access/transam/README,v 1.2 2004/09/16 16:58:26 tgl Exp $
 
 The Transaction System
 ----------------------
@@ -9,7 +9,7 @@ the mainloop's control code, which in turn implements user-visible
 transactions and savepoints.
 
 The middle layer of code is called by postgres.c before and after the
-processing of each query:
+processing of each query, or after detecting an error:
 
 		StartTransactionCommand
 		CommitTransactionCommand
@@ -44,9 +44,9 @@ effects of previous commands within the same transaction.  Note that this is
 done automatically by CommitTransactionCommand after each query inside a
 transaction block, but some utility functions also do it internally to allow
 some operations (usually in the system catalogs) to be seen by future
-operations in the same utility command (for example, in DefineRelation it is
+operations in the same utility command.  (For example, in DefineRelation it is
 done after creating the heap so the pg_class row is visible, to be able to
-lock it).
+lock it.)
 
 
 For example, consider the following sequence of user commands:
@@ -60,26 +60,26 @@ In the main processing loop, this results in the following function call
 sequence:
 
 	 /	StartTransactionCommand;
-	/	ProcessUtility;				<< BEGIN
-1) <			BeginTransactionBlock;
-	\	CommitTransactionCommand;
-	 \		StartTransaction;
+	/		StartTransaction;
+1) <		ProcessUtility;				<< BEGIN
+	\		BeginTransactionBlock;
+	 \	CommitTransactionCommand;
 
 	/	StartTransactionCommand;
-2) /		ProcessQuery;				<< SELECT * FROM foo
+2) /		ProcessQuery;				<< SELECT ...
    \		CommitTransactionCommand;
 	\		CommandCounterIncrement;
 
 	/	StartTransactionCommand;
-3) /		ProcessQuery;				<< INSERT INTO foo VALUES (...)
+3) /		ProcessQuery;				<< INSERT ...
    \		CommitTransactionCommand;
 	\		CommandCounterIncrement;
 
 	 /	StartTransactionCommand;
 	/	ProcessUtility;				<< COMMIT
 4) <			EndTransactionBlock;
-	\			CommitTransaction;
-	 \	CommitTransactionCommand;
+	\	CommitTransactionCommand;
+	 \		CommitTransaction;
 
 The point of this example is to demonstrate the need for
 StartTransactionCommand and CommitTransactionCommand to be state smart -- they
@@ -118,7 +118,7 @@ to do all the real work.  The only difference is what state we enter after
 AbortTransaction does its work:
 
 * AbortCurrentTransaction leaves us in TBLOCK_ABORT,
-* UserAbortTransactionBlock leaves us in TBLOCK_ENDABORT
+* UserAbortTransactionBlock leaves us in TBLOCK_ABORT_END
 
 Low-level transaction abort handling is divided in two phases:
 * AbortTransaction executes as soon as we realize the transaction has
@@ -126,7 +126,7 @@ Low-level transaction abort handling is divided in two phases:
   not delay other backends unnecessarily.
 * CleanupTransaction executes when we finally see a user COMMIT
   or ROLLBACK command; it cleans things up and gets us out of the transaction
-  internally.  In particular, we mustn't destroy TopTransactionContext until
+  completely.  In particular, we mustn't destroy TopTransactionContext until
   this point.
 
 Also, note that when a transaction is committed, we don't close it right away.
@@ -163,28 +163,48 @@ called so the system returns to the parent transaction.
 One important point regarding subtransaction handling is that several may need
 to be closed in response to a single user command.  That's because savepoints
 have names, and we allow to commit or rollback a savepoint by name, which is
-not necessarily the one that was last opened.  In the case of subtransaction
-commit this is not a problem, and we close all the involved subtransactions
-right away by calling CommitTransactionToLevel, which in turn calls
-CommitSubTransaction and PopTransaction as many times as needed.
-
-In the case of subtransaction abort (when the user issues ROLLBACK TO
-<savepoint>), things are not so easy.  We have to keep the subtransactions
-open and return control to the main loop.  So what RollbackToSavepoint does is
-abort the innermost subtransaction and put it in TBLOCK_SUBENDABORT state, and
-put the rest in TBLOCK_SUBABORT_PENDING state.  Then we return control to the
-main loop, which will in turn return control to us by calling
-CommitTransactionCommand.  At this point we can close all subtransactions that
-are marked with the "abort pending" state.  When that's done, the outermost
-subtransaction is created again, to conform to SQL's definition of ROLLBACK TO.
+not necessarily the one that was last opened.  Also a COMMIT or ROLLBACK
+command must be able to close out the entire stack.  We handle this by having
+the utility command subroutine mark all the state stack entries as commit-
+pending or abort-pending, and then when the main loop reaches
+CommitTransactionCommand, the real work is done.  The main point of doing
+things this way is that if we get an error while popping state stack entries,
+the remaining stack entries still show what we need to do to finish up.
+
+In the case of ROLLBACK TO <savepoint>, we abort all the subtransactions up
+through the one identified by the savepoint name, and then re-create that
+subtransaction level with the same name.  So it's a completely new
+subtransaction as far as the internals are concerned.
 
 Other subsystems are allowed to start "internal" subtransactions, which are
 handled by BeginInternalSubtransaction.  This is to allow implementing
 exception handling, e.g. in PL/pgSQL.  ReleaseCurrentSubTransaction and
 RollbackAndReleaseCurrentSubTransaction allows the subsystem to close said
 subtransactions.  The main difference between this and the savepoint/release
-path is that BeginInternalSubtransaction is allowed when no explicit
-transaction block has been established, while DefineSavepoint is not.
+path is that we execute the complete state transition immediately in each
+subroutine, rather than deferring some work until CommitTransactionCommand.
+Another difference is that BeginInternalSubtransaction is allowed when no
+explicit transaction block has been established, while DefineSavepoint is not.
+
+
+Subtransaction numbering
+------------------------
+
+A top-level transaction is always given a TransactionId (XID) as soon as it is
+created.  This is necessary for a number of reasons, notably XMIN bookkeeping
+for VACUUM.  However, a subtransaction doesn't need its own XID unless it
+(or one of its child subxacts) writes tuples into the database.  Therefore,
+we postpone assigning XIDs to subxacts until and unless they call
+GetCurrentTransactionId.  The subsidiary actions of obtaining a lock on the
+XID and and entering it into pg_subtrans and PG_PROC are done at the same time.
+
+Internally, a backend needs a way to identify subtransactions whether or not
+they have XIDs; but this need only lasts as long as the parent top transaction
+endures.  Therefore, we have SubTransactionId, which is somewhat like
+CommandId in that it's generated from a counter that we reset at the start of
+each top transaction.  The top-level transaction itself has SubTransactionId 1,
+and subtransactions have IDs 2 and up.  (Zero is reserved for
+InvalidSubTransactionId.)
 
 
 pg_clog and pg_subtrans
@@ -197,27 +217,28 @@ there's a long running transaction or a backend sitting idle with an open
 transaction, it may be necessary to be able to read and write this information
 from disk.  They also allow information to be permanent across server restarts.
 
-pg_clog records the commit status for each transaction.  A transaction can be
-in progress, committed, aborted, or "sub-committed".  This last state means
-that it's a subtransaction that's no longer running, but its parent has not
-updated its state yet (either it is still running, or the backend crashed
-without updating its status).  A sub-committed transaction's status will be
-updated again to the final value as soon as the parent commits or aborts, or
-when the parent is detected to be aborted.
+pg_clog records the commit status for each transaction that has been assigned
+an XID.  A transaction can be in progress, committed, aborted, or
+"sub-committed".  This last state means that it's a subtransaction that's no
+longer running, but its parent has not updated its state yet (either it is
+still running, or the backend crashed without updating its status).  A
+sub-committed transaction's status will be updated again to the final value as
+soon as the parent commits or aborts, or when the parent is detected to be
+aborted.
 
 Savepoints are implemented using subtransactions.  A subtransaction is a
-transaction inside a transaction; it gets its own TransactionId, but its
-commit or abort status is not only dependent on whether it committed itself,
-but also whether its parent transaction committed.  To implement multiple
-savepoints in a transaction we allow unlimited transaction nesting depth, so
-any particular subtransaction's commit state is dependent on the commit status
-of each and every ancestor transaction.
+transaction inside a transaction; its commit or abort status is not only
+dependent on whether it committed itself, but also whether its parent
+transaction committed.  To implement multiple savepoints in a transaction we
+allow unlimited transaction nesting depth, so any particular subtransaction's
+commit state is dependent on the commit status of each and every ancestor
+transaction.
 
 The "subtransaction parent" (pg_subtrans) mechanism records, for each
-transaction, the TransactionId of its parent transaction.  This information is
-stored as soon as the subtransaction is created.  Top-level transactions do
-not have a parent, so they leave their pg_subtrans entries set to the default
-value of zero (InvalidTransactionId).
+transaction with an XID, the TransactionId of its parent transaction.  This
+information is stored as soon as the subtransaction is assigned an XID.
+Top-level transactions do not have a parent, so they leave their pg_subtrans
+entries set to the default value of zero (InvalidTransactionId).
 
 pg_subtrans is used to check whether the transaction in question is still
 running --- the main Xid of a transaction is recorded in the PGPROC struct,
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index ffcc324eb3e..fe99ba15f36 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.188 2004/09/13 20:06:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.189 2004/09/16 16:58:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -46,6 +46,19 @@
 
 
 /*
+ *	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
@@ -59,29 +72,33 @@ typedef enum 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,
-	TBLOCK_STARTED,
+	TBLOCK_DEFAULT,				/* idle */
+	TBLOCK_STARTED,				/* running single-query transaction */
 
 	/* transaction block states */
-	TBLOCK_BEGIN,
-	TBLOCK_INPROGRESS,
-	TBLOCK_END,
-	TBLOCK_ABORT,
-	TBLOCK_ENDABORT,
+	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 */
 
 	/* subtransaction states */
-	TBLOCK_SUBBEGIN,
-	TBLOCK_SUBINPROGRESS,
-	TBLOCK_SUBEND,
-	TBLOCK_SUBABORT,
-	TBLOCK_SUBABORT_PENDING,
-	TBLOCK_SUBENDABORT_ALL,
-	TBLOCK_SUBENDABORT_RELEASE,
-	TBLOCK_SUBENDABORT
+	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;
 
 /*
@@ -89,10 +106,10 @@ typedef enum TBlockState
  */
 typedef struct TransactionStateData
 {
-	TransactionId transactionIdData;	/* my XID */
+	TransactionId transactionId;		/* my XID, or Invalid if none */
+	SubTransactionId subTransactionId;	/* my subxact ID */
 	char	   *name;			/* savepoint name, if any */
 	int			savepointLevel; /* savepoint level */
-	CommandId	commandId;		/* current CID */
 	TransState	state;			/* low-level state */
 	TBlockState blockState;		/* high-level state */
 	int			nestingLevel;	/* nest depth */
@@ -115,42 +132,6 @@ typedef TransactionStateData *TransactionState;
 #define lfirst_xid(lc)				((TransactionId) lfirst_int(lc))
 #define lappend_xid(list, datum)	lappend_int(list, (int) (datum))
 
-
-static void AbortTransaction(void);
-static void AtAbort_Memory(void);
-static void AtCleanup_Memory(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, TransactionId parentXid);
-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 StartAbortedSubTransaction(void);
-static void PushTransaction(void);
-static void PopTransaction(void);
-static char *CleanupAbortedSubTransactions(bool returnName);
-
-static void AtSubAbort_Memory(void);
-static void AtSubCleanup_Memory(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);
-
 /*
  * CurrentTransactionState always points to the current transaction state
  * block.  It will point to TopTransactionStateData when not in a
@@ -158,9 +139,9 @@ static const char *TransStateAsString(TransState state);
  */
 static TransactionStateData TopTransactionStateData = {
 	0,							/* transaction id */
+	0,							/* subtransaction id */
 	NULL,						/* savepoint name */
 	0,							/* savepoint level */
-	FirstCommandId,				/* command id */
 	TRANS_DEFAULT,				/* transaction state */
 	TBLOCK_DEFAULT,				/* transaction block state from the client
 								 * perspective */
@@ -176,6 +157,13 @@ static TransactionStateData TopTransactionStateData = {
 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;
+
+/*
  * These vars hold the value of now(), ie, the transaction start time.
  * This does not change as we enter and exit subtransactions, so we don't
  * keep it inside the TransactionState stack.
@@ -185,20 +173,6 @@ static int	xactStartTimeUsec;	/* microsecond part */
 
 
 /*
- *	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; /* number of concurrent xacts needed to
-								 * sleep */
-
-
-/*
  * List of add-on start- and end-of-xact callbacks
  */
 typedef struct XactCallbackItem
@@ -210,10 +184,61 @@ typedef struct 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;
+
 static void (*_RollbackFunc) (void *) = NULL;
 static void *_RollbackData = 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 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 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
  * ----------------------------------------------------------------
@@ -278,19 +303,99 @@ IsAbortedTransactionBlockState(void)
 TransactionId
 GetTopTransactionId(void)
 {
-	return TopTransactionStateData.transactionIdData;
+	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;
 
-	return s->transactionIdData;
+	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;
 }
 
 
@@ -300,9 +405,8 @@ GetCurrentTransactionId(void)
 CommandId
 GetCurrentCommandId(void)
 {
-	TransactionState s = CurrentTransactionState;
-
-	return s->commandId;
+	/* this is global to a transaction, not subtransaction-local */
+	return currentCommandId;
 }
 
 
@@ -374,7 +478,9 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
 
 		if (s->state == TRANS_ABORT)
 			continue;
-		if (TransactionIdEquals(xid, s->transactionIdData))
+		if (!TransactionIdIsValid(s->transactionId))
+			continue;			/* it can't have any child XIDs either */
+		if (TransactionIdEquals(xid, s->transactionId))
 			return true;
 		foreach(cell, s->childXids)
 		{
@@ -393,19 +499,20 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
 void
 CommandCounterIncrement(void)
 {
-	TransactionState s = CurrentTransactionState;
-
-	s->commandId += 1;
-	if (s->commandId == FirstCommandId) /* check for overflow */
+	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 = s->commandId;
+		SerializableSnapshot->curcid = currentCommandId;
 	if (LatestSnapshot)
-		LatestSnapshot->curcid = s->commandId;
+		LatestSnapshot->curcid = currentCommandId;
 
 	/*
 	 * make cache changes visible to me.
@@ -786,7 +893,7 @@ AtSubCommit_childXids(void)
 	old_cxt = MemoryContextSwitchTo(s->parent->curTransactionContext);
 
 	s->parent->childXids = lappend_xid(s->parent->childXids,
-									   s->transactionIdData);
+									   s->transactionId);
 
 	s->parent->childXids = list_concat(s->parent->childXids, s->childXids);
 	s->childXids = NIL;			/* ensure list not doubly referenced */
@@ -1063,7 +1170,8 @@ RecordSubTransactionAbort(void)
 
 		/*
 		 * Mark the transaction aborted in clog.  This is not absolutely
-		 * necessary but we may as well do it while we are here.
+		 * necessary but XactLockTableWait makes use of it to avoid waiting
+		 * for already-aborted subtransactions.
 		 */
 		TransactionIdAbort(xid);
 		TransactionIdAbortTree(nchildren, children);
@@ -1142,7 +1250,9 @@ AtSubCleanup_Memory(void)
 	 * can go too (note this also kills CurTransactionContexts from any
 	 * children of the subxact).
 	 */
-	MemoryContextDelete(s->curTransactionContext);
+	if (s->curTransactionContext)
+		MemoryContextDelete(s->curTransactionContext);
+	s->curTransactionContext = NULL;
 }
 
 /* ----------------------------------------------------------------
@@ -1156,7 +1266,13 @@ AtSubCleanup_Memory(void)
 static void
 StartTransaction(void)
 {
-	TransactionState s = CurrentTransactionState;
+	TransactionState s;
+
+	/*
+	 * Let's just make sure the state stack is empty
+	 */
+	s = &TopTransactionStateData;
+	CurrentTransactionState = s;
 
 	/*
 	 * check the current transaction state
@@ -1180,6 +1296,13 @@ StartTransaction(void)
 	XactReadOnly = DefaultXactReadOnly;
 
 	/*
+	 * reinitialize within-transaction counters
+	 */
+	s->subTransactionId = TopSubTransactionId;
+	currentSubTransactionId = TopSubTransactionId;
+	currentCommandId = FirstCommandId;
+
+	/*
 	 * must initialize resource-management stuff first
 	 */
 	AtStart_Memory();
@@ -1188,9 +1311,9 @@ StartTransaction(void)
 	/*
 	 * generate a new transaction id
 	 */
-	s->transactionIdData = GetNewTransactionId(false);
+	s->transactionId = GetNewTransactionId(false);
 
-	XactLockTableInsert(s->transactionIdData);
+	XactLockTableInsert(s->transactionId);
 
 	/*
 	 * set now()
@@ -1200,7 +1323,6 @@ StartTransaction(void)
 	/*
 	 * initialize current transaction state fields
 	 */
-	s->commandId = FirstCommandId;
 	s->nestingLevel = 1;
 	s->childXids = NIL;
 
@@ -1332,7 +1454,7 @@ CommitTransaction(void)
 	 * backend-wide state.
 	 */
 
-	CallXactCallbacks(XACT_EVENT_COMMIT, InvalidTransactionId);
+	CallXactCallbacks(XACT_EVENT_COMMIT);
 
 	ResourceOwnerRelease(TopTransactionResourceOwner,
 						 RESOURCE_RELEASE_BEFORE_LOCKS,
@@ -1365,7 +1487,7 @@ CommitTransaction(void)
 
 	AtEOXact_GUC(true, false);
 	AtEOXact_SPI(true);
-	AtEOXact_on_commit_actions(true, s->transactionIdData);
+	AtEOXact_on_commit_actions(true);
 	AtEOXact_Namespace(true);
 	/* smgrcommit already done */
 	AtEOXact_Files();
@@ -1379,6 +1501,8 @@ CommitTransaction(void)
 
 	AtCommit_Memory();
 
+	s->transactionId = InvalidTransactionId;
+	s->subTransactionId = InvalidSubTransactionId;
 	s->nestingLevel = 0;
 	s->childXids = NIL;
 
@@ -1486,7 +1610,7 @@ AbortTransaction(void)
 	 * ordering.
 	 */
 
-	CallXactCallbacks(XACT_EVENT_ABORT, InvalidTransactionId);
+	CallXactCallbacks(XACT_EVENT_ABORT);
 
 	ResourceOwnerRelease(TopTransactionResourceOwner,
 						 RESOURCE_RELEASE_BEFORE_LOCKS,
@@ -1502,7 +1626,7 @@ AbortTransaction(void)
 
 	AtEOXact_GUC(false, false);
 	AtEOXact_SPI(false);
-	AtEOXact_on_commit_actions(false, s->transactionIdData);
+	AtEOXact_on_commit_actions(false);
 	AtEOXact_Namespace(false);
 	smgrabort();
 	AtEOXact_Files();
@@ -1535,13 +1659,16 @@ CleanupTransaction(void)
 	AtCleanup_Portals();		/* now safe to release portal memory */
 
 	CurrentResourceOwner = NULL;	/* and resource owner */
-	ResourceOwnerDelete(TopTransactionResourceOwner);
+	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;
 
@@ -1572,20 +1699,23 @@ StartTransactionCommand(void)
 			break;
 
 			/*
-			 * This is the case when we are somewhere in a transaction
-			 * block and about to start a new command.	For now we do
-			 * nothing but someday we may do command-local resource
-			 * initialization.
+			 * 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 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 to the "END
-			 * TRANSACTION" which will set things straight.
+			 * 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:
@@ -1597,12 +1727,13 @@ StartTransactionCommand(void)
 		case TBLOCK_SUBBEGIN:
 		case TBLOCK_END:
 		case TBLOCK_SUBEND:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
-		case TBLOCK_ENDABORT:
-			elog(FATAL, "StartTransactionCommand: unexpected state %s",
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
+			elog(ERROR, "StartTransactionCommand: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
 	}
@@ -1628,18 +1759,16 @@ CommitTransactionCommand(void)
 			/*
 			 * This shouldn't happen, because it means the previous
 			 * StartTransactionCommand didn't set the STARTED state
-			 * appropriately, or we didn't manage previous pending abort
-			 * states.
+			 * appropriately.
 			 */
 		case TBLOCK_DEFAULT:
-		case TBLOCK_SUBABORT_PENDING:
 			elog(FATAL, "CommitTransactionCommand: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
 
 			/*
 			 * If we aren't in a transaction block, just do our usual
-			 * transaction commit.
+			 * transaction commit, and return to the idle state.
 			 */
 		case TBLOCK_STARTED:
 			CommitTransaction();
@@ -1647,10 +1776,10 @@ CommitTransactionCommand(void)
 			break;
 
 			/*
-			 * This is the case right after we get a "BEGIN TRANSACTION"
-			 * command, but the user hasn't done anything else yet, so we
+			 * We are completing a "BEGIN TRANSACTION" command, so we
 			 * change to the "transaction block in progress" state and
-			 * return.
+			 * return.  (We assume the BEGIN did nothing to the database,
+			 * so we need no CommandCounterIncrement.)
 			 */
 		case TBLOCK_BEGIN:
 			s->blockState = TBLOCK_INPROGRESS;
@@ -1662,13 +1791,13 @@ CommitTransactionCommand(void)
 			 * command counter and return.
 			 */
 		case TBLOCK_INPROGRESS:
+		case TBLOCK_SUBINPROGRESS:
 			CommandCounterIncrement();
 			break;
 
 			/*
-			 * This is the case when we just got the "END TRANSACTION"
-			 * statement, so we commit the transaction and go back to the
-			 * default state.
+			 * We are completing a "COMMIT" command.  Do it and return to
+			 * the idle state.
 			 */
 		case TBLOCK_END:
 			CommitTransaction();
@@ -1678,32 +1807,31 @@ CommitTransactionCommand(void)
 			/*
 			 * 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 to the "END
-			 * TRANSACTION" which will set things straight.
+			 * 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 which just
-			 * processed the "END TRANSACTION" command from the user, so
-			 * clean up and return to the default state.
+			 * 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_ENDABORT:
+		case TBLOCK_ABORT_END:
 			CleanupTransaction();
 			s->blockState = TBLOCK_DEFAULT;
 			break;
 
 			/*
-			 * Ditto, but in a subtransaction.	AbortOutOfAnyTransaction
-			 * will do the dirty work.
+			 * 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_SUBENDABORT_ALL:
-			AbortOutOfAnyTransaction();
-			s = CurrentTransactionState;		/* changed by
-												 * AbortOutOfAnyTransaction
-												 * */
-			/* AbortOutOfAnyTransaction sets the blockState */
+		case TBLOCK_ABORT_PENDING:
+			AbortTransaction();
+			CleanupTransaction();
+			s->blockState = TBLOCK_DEFAULT;
 			break;
 
 			/*
@@ -1718,23 +1846,15 @@ CommitTransactionCommand(void)
 			break;
 
 			/*
-			 * Inside a subtransaction, increment the command counter.
-			 */
-		case TBLOCK_SUBINPROGRESS:
-			CommandCounterIncrement();
-			break;
-
-			/*
 			 * We were issued a COMMIT or RELEASE command, so we end the
 			 * current subtransaction and return to the parent transaction.
-			 * Lather, rinse, and repeat until we get out of all SUBEND'ed
-			 * subtransaction levels.
+			 * 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();
-				PopTransaction();
 				s = CurrentTransactionState;	/* changed by pop */
 			} while (s->blockState == TBLOCK_SUBEND);
 			/* If we had a COMMIT command, finish off the main xact too */
@@ -1744,36 +1864,54 @@ CommitTransactionCommand(void)
 				CommitTransaction();
 				s->blockState = TBLOCK_DEFAULT;
 			}
+			else
+			{
+				Assert(s->blockState == TBLOCK_INPROGRESS ||
+					   s->blockState == TBLOCK_SUBINPROGRESS);
+			}
 			break;
 
 			/*
-			 * If we are in an aborted subtransaction, do nothing.
+			 * 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:
+		case TBLOCK_SUBABORT_END:
+			CleanupSubTransaction();
+			CommitTransactionCommand();
 			break;
 
 			/*
-			 * The current subtransaction is ending.  Do the equivalent of
-			 * a ROLLBACK TO followed by a RELEASE command.
+			 * As above, but it's not dead yet, so abort first.
 			 */
-		case TBLOCK_SUBENDABORT_RELEASE:
-			CleanupAbortedSubTransactions(false);
+		case TBLOCK_SUBABORT_PENDING:
+			AbortSubTransaction();
+			CleanupSubTransaction();
+			CommitTransactionCommand();
 			break;
 
 			/*
-			 * The current subtransaction is ending due to a ROLLBACK TO
-			 * command, so close all savepoints up to the target level.
-			 * When finished, recreate the savepoint.
+			 * 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_SUBENDABORT:
+		case TBLOCK_SUBRESTART:
 			{
-				char	   *name = CleanupAbortedSubTransactions(true);
+				char	   *name;
+				int			savepointLevel;
+
+				/* save name and keep Cleanup from freeing it */
+				name = s->name;
+				s->name = NULL;
+				savepointLevel = s->savepointLevel;
+
+				AbortSubTransaction();
+				CleanupSubTransaction();
 
-				Assert(PointerIsValid(name));
-				DefineSavepoint(name);
-				s = CurrentTransactionState;	/* changed by
-												 * DefineSavepoint */
-				pfree(name);
+				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);
@@ -1781,56 +1919,35 @@ CommitTransactionCommand(void)
 				s->blockState = TBLOCK_SUBINPROGRESS;
 			}
 			break;
-	}
-}
 
-/*
- * CleanupAbortedSubTransactions
- *
- * Helper function for CommitTransactionCommand.  Aborts and cleans up
- * dead subtransactions after a ROLLBACK TO command.  Optionally returns
- * the name of the last dead subtransaction so it can be reused to redefine
- * the savepoint.  (Caller is responsible for pfree'ing the result.)
- */
-static char *
-CleanupAbortedSubTransactions(bool returnName)
-{
-	TransactionState s = CurrentTransactionState;
-	char	   *name = NULL;
+			/*
+			 * Same as above, but the subtransaction had already failed,
+			 * so we don't need AbortSubTransaction.
+			 */
+		case TBLOCK_SUBABORT_RESTART:
+			{
+				char	   *name;
+				int			savepointLevel;
 
-	AssertState(PointerIsValid(s->parent));
-	Assert(s->parent->blockState == TBLOCK_SUBINPROGRESS ||
-		   s->parent->blockState == TBLOCK_INPROGRESS ||
-		   s->parent->blockState == TBLOCK_STARTED ||
-		   s->parent->blockState == TBLOCK_SUBABORT_PENDING);
+				/* save name and keep Cleanup from freeing it */
+				name = s->name;
+				s->name = NULL;
+				savepointLevel = s->savepointLevel;
 
-	/*
-	 * Abort everything up to the target level.  The current
-	 * subtransaction only needs cleanup.  If we need to save the name,
-	 * look for the last subtransaction in TBLOCK_SUBABORT_PENDING state.
-	 */
-	if (returnName && s->parent->blockState != TBLOCK_SUBABORT_PENDING)
-		name = MemoryContextStrdup(TopMemoryContext, s->name);
+				CleanupSubTransaction();
 
-	CleanupSubTransaction();
-	PopTransaction();
-	s = CurrentTransactionState;	/* changed by pop */
+				DefineSavepoint(NULL);
+				s = CurrentTransactionState;	/* changed by push */
+				s->name = name;
+				s->savepointLevel = savepointLevel;
 
-	while (s->blockState == TBLOCK_SUBABORT_PENDING)
-	{
-		AbortSubTransaction();
-		if (returnName && s->parent->blockState != TBLOCK_SUBABORT_PENDING)
-			name = MemoryContextStrdup(TopMemoryContext, s->name);
-		CleanupSubTransaction();
-		PopTransaction();
-		s = CurrentTransactionState;
+				/* This is the same as TBLOCK_SUBBEGIN case */
+				AssertState(s->blockState == TBLOCK_SUBBEGIN);
+				StartSubTransaction();
+				s->blockState = TBLOCK_SUBINPROGRESS;
+			}
+			break;
 	}
-
-	AssertState(s->blockState == TBLOCK_SUBINPROGRESS ||
-				s->blockState == TBLOCK_INPROGRESS ||
-				s->blockState == TBLOCK_STARTED);
-
-	return name;
 }
 
 /*
@@ -1861,32 +1978,32 @@ AbortCurrentTransaction(void)
 
 			/*
 			 * If we are in TBLOCK_BEGIN it means something screwed up
-			 * right after reading "BEGIN TRANSACTION" so we enter the
-			 * abort state.  Eventually an "END TRANSACTION" will fix
-			 * things.
+			 * 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();
-			s->blockState = TBLOCK_ABORT;
-			/* CleanupTransaction happens when we exit TBLOCK_ENDABORT */
+			CleanupTransaction();
+			s->blockState = TBLOCK_DEFAULT;
 			break;
 
 			/*
-			 * This is the case when 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 an "END TRANSACTION".
+			 * 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_ENDABORT */
+			/* CleanupTransaction happens when we exit TBLOCK_ABORT_END */
 			break;
 
 			/*
-			 * Here, the system was fouled up just after the user wanted
-			 * to end the transaction block so we abort the transaction
-			 * and return to the default state.
+			 * 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();
@@ -1896,74 +2013,65 @@ AbortCurrentTransaction(void)
 
 			/*
 			 * Here, we are already in an aborted transaction state and
-			 * are waiting for an "END TRANSACTION" to come along and lo
-			 * and behold, we abort again! So we just remain in the abort
-			 * state.
+			 * 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;
 
 			/*
-			 * Here we were in an aborted transaction block which just
-			 * processed the "END TRANSACTION" command but somehow aborted
-			 * again.. since we must have done the abort processing, we
-			 * clean up and return to the default state.
+			 * 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_ENDABORT:
+		case TBLOCK_ABORT_END:
 			CleanupTransaction();
 			s->blockState = TBLOCK_DEFAULT;
 			break;
 
 			/*
-			 * If we are just starting a subtransaction, put it in aborted
-			 * state.
+			 * We are in a live transaction and we got a ROLLBACK command.
+			 * Abort, cleanup, go to idle state.
 			 */
-		case TBLOCK_SUBBEGIN:
-			StartAbortedSubTransaction();
-			s->blockState = TBLOCK_SUBABORT;
+		case TBLOCK_ABORT_PENDING:
+			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 are aborting an ending transaction, we have to abort
-			 * the parent transaction too.
+			 * 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();
-			PopTransaction();
-			s = CurrentTransactionState;		/* changed by pop */
-			Assert(s->blockState != TBLOCK_SUBEND &&
-				   s->blockState != TBLOCK_SUBENDABORT);
 			AbortCurrentTransaction();
 			break;
 
 			/*
 			 * Same as above, except the Abort() was already done.
 			 */
-		case TBLOCK_SUBENDABORT:
-		case TBLOCK_SUBENDABORT_RELEASE:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_SUBABORT_RESTART:
 			CleanupSubTransaction();
-			PopTransaction();
-			s = CurrentTransactionState;		/* changed by pop */
-			Assert(s->blockState != TBLOCK_SUBEND &&
-				   s->blockState != TBLOCK_SUBENDABORT);
 			AbortCurrentTransaction();
 			break;
-
-			/*
-			 * We are already aborting the whole transaction tree. Do
-			 * nothing, CommitTransactionCommand will call
-			 * AbortOutOfAnyTransaction and set things straight.
-			 */
-		case TBLOCK_SUBENDABORT_ALL:
-			break;
 	}
 }
 
@@ -2113,9 +2221,7 @@ IsInTransactionChain(void *stmtNode)
  * (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.	At subtransaction
- * start, the callback is called when the subtransaction has finished
- * initializing.
+ * callback functions can only do noncritical cleanup.
  */
 void
 RegisterXactCallback(XactCallback callback, void *arg)
@@ -2152,12 +2258,69 @@ UnregisterXactCallback(XactCallback callback, void *arg)
 }
 
 static void
-CallXactCallbacks(XactEvent event, TransactionId parentXid)
+CallXactCallbacks(XactEvent event)
 {
 	XactCallbackItem *item;
 
 	for (item = Xact_callbacks; item; item = item->next)
-		(*item->callback) (event, parentXid, item->arg);
+		(*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);
 }
 
 
@@ -2197,17 +2360,18 @@ BeginTransactionBlock(void)
 				  errmsg("there is already a transaction in progress")));
 			break;
 
-			/* These cases are invalid.  Reject them altogether. */
+			/* These cases are invalid. */
 		case TBLOCK_DEFAULT:
 		case TBLOCK_BEGIN:
 		case TBLOCK_SUBBEGIN:
-		case TBLOCK_ENDABORT:
 		case TBLOCK_END:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
-		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
 		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:
 			elog(FATAL, "BeginTransactionBlock: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2220,6 +2384,11 @@ BeginTransactionBlock(void)
  *
  * 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)
@@ -2230,11 +2399,8 @@ EndTransactionBlock(void)
 	switch (s->blockState)
 	{
 			/*
-			 * We are in a transaction block which should commit when we
-			 * get to the upcoming CommitTransactionCommand() so we set
-			 * the state to "END".	CommitTransactionCommand() will
-			 * recognize this and commit the transaction and return us to
-			 * the default state.
+			 * We are in a transaction block, so tell CommitTransactionCommand
+			 * to COMMIT.
 			 */
 		case TBLOCK_INPROGRESS:
 			s->blockState = TBLOCK_END;
@@ -2242,14 +2408,11 @@ EndTransactionBlock(void)
 			break;
 
 			/*
-			 * We are in a transaction block which aborted. Since the
-			 * AbortTransaction() was already done, we need only change to
-			 * the special "END ABORT" state.  The upcoming
-			 * CommitTransactionCommand() will recognise this and then put
-			 * us back in the default state.
+			 * We are in a failed transaction block.  Tell
+			 * CommitTransactionCommand it's time to exit the block.
 			 */
 		case TBLOCK_ABORT:
-			s->blockState = TBLOCK_ENDABORT;
+			s->blockState = TBLOCK_ABORT_END;
 			break;
 
 			/*
@@ -2259,50 +2422,72 @@ EndTransactionBlock(void)
 		case TBLOCK_SUBINPROGRESS:
 			while (s->parent != NULL)
 			{
-				Assert(s->blockState == TBLOCK_SUBINPROGRESS);
-				s->blockState = TBLOCK_SUBEND;
+				if (s->blockState == TBLOCK_SUBINPROGRESS)
+					s->blockState = TBLOCK_SUBEND;
+				else
+					elog(FATAL, "EndTransactionBlock: unexpected state %s",
+						 BlockStateAsString(s->blockState));
 				s = s->parent;
 			}
-			Assert(s->blockState == TBLOCK_INPROGRESS);
-			s->blockState = TBLOCK_END;
+			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.  Go to the
-			 * "abort the whole tree" state so that
-			 * CommitTransactionCommand() calls AbortOutOfAnyTransaction.
+			 * 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:
-			s->blockState = TBLOCK_SUBENDABORT_ALL;
+			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;
 
-		case TBLOCK_STARTED:
-
 			/*
 			 * here, the user issued COMMIT 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")));
-			AbortTransaction();
-			s->blockState = TBLOCK_ENDABORT;
+			s->blockState = TBLOCK_ABORT_PENDING;
 			break;
 
-			/* these cases are invalid. */
+			/* These cases are invalid. */
 		case TBLOCK_DEFAULT:
 		case TBLOCK_BEGIN:
-		case TBLOCK_ENDABORT:
-		case TBLOCK_END:
 		case TBLOCK_SUBBEGIN:
+		case TBLOCK_END:
 		case TBLOCK_SUBEND:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "EndTransactionBlock: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2314,6 +2499,8 @@ EndTransactionBlock(void)
 /*
  *	UserAbortTransactionBlock
  *		This executes a ROLLBACK command.
+ *
+ * As above, we don't actually do anything here except change blockState.
  */
 void
 UserAbortTransactionBlock(void)
@@ -2323,46 +2510,48 @@ UserAbortTransactionBlock(void)
 	switch (s->blockState)
 	{
 			/*
-			 * We are inside a failed transaction block and we got an
-			 * abort command from the user.  Abort processing is already
-			 * done, we just need to move to the ENDABORT state so we will
-			 * end up in the default state after the upcoming
-			 * CommitTransactionCommand().
+			 * 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_ABORT:
-			s->blockState = TBLOCK_ENDABORT;
+		case TBLOCK_INPROGRESS:
+			s->blockState = TBLOCK_ABORT_PENDING;
 			break;
 
 			/*
-			 * We are inside a failed subtransaction and we got an abort
+			 * We are inside a failed transaction block and we got a ROLLBACK
 			 * command from the user.  Abort processing is already done,
-			 * so go to the "abort all" state and CommitTransactionCommand
-			 * will call AbortOutOfAnyTransaction to set things straight.
-			 */
-		case TBLOCK_SUBABORT:
-			s->blockState = TBLOCK_SUBENDABORT_ALL;
-			break;
-
-			/*
-			 * We are inside a transaction block and we got an abort
-			 * command from the user, so we move to the ENDABORT state and
-			 * do abort processing so we will end up in the default state
-			 * after the upcoming CommitTransactionCommand().
+			 * so CommitTransactionCommand just has to cleanup and go back
+			 * to idle state.
 			 */
-		case TBLOCK_INPROGRESS:
-			AbortTransaction();
-			s->blockState = TBLOCK_ENDABORT;
+		case TBLOCK_ABORT:
+			s->blockState = TBLOCK_ABORT_END;
 			break;
 
 			/*
-			 * We are inside a subtransaction.	Abort the current
-			 * subtransaction and go to the "abort all" state, so
-			 * CommitTransactionCommand will call AbortOutOfAnyTransaction
-			 * to set things straight.
+			 * We are inside a subtransaction.  Mark everything
+			 * up to top level as exitable.
 			 */
 		case TBLOCK_SUBINPROGRESS:
-			AbortSubTransaction();
-			s->blockState = TBLOCK_SUBENDABORT_ALL;
+		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;
 
 			/*
@@ -2375,21 +2564,21 @@ UserAbortTransactionBlock(void)
 			ereport(WARNING,
 					(errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
 					 errmsg("there is no transaction in progress")));
-			AbortTransaction();
-			s->blockState = TBLOCK_ENDABORT;
+			s->blockState = TBLOCK_ABORT_PENDING;
 			break;
 
 			/* These cases are invalid. */
 		case TBLOCK_DEFAULT:
 		case TBLOCK_BEGIN:
+		case TBLOCK_SUBBEGIN:
 		case TBLOCK_END:
-		case TBLOCK_ENDABORT:
 		case TBLOCK_SUBEND:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
-		case TBLOCK_SUBBEGIN:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2414,28 +2603,28 @@ DefineSavepoint(char *name)
 			s = CurrentTransactionState;		/* changed by push */
 
 			/*
-			 * Note that we are allocating the savepoint name in the
-			 * parent transaction's CurTransactionContext, since we don't
-			 * yet have a transaction context for the new guy.
+			 * Savepoint names, like the TransactionState block itself,
+			 * live in TopTransactionContext.
 			 */
-			s->name = MemoryContextStrdup(CurTransactionContext, name);
-			s->blockState = TBLOCK_SUBBEGIN;
+			if (name)
+				s->name = MemoryContextStrdup(TopTransactionContext, name);
 			break;
 
-			/* These cases are invalid.  Reject them altogether. */
+			/* 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_ENDABORT:
-		case TBLOCK_END:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
-		case TBLOCK_SUBEND:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "DefineSavepoint: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2445,6 +2634,8 @@ DefineSavepoint(char *name)
 /*
  * ReleaseSavepoint
  *		This executes a RELEASE command.
+ *
+ * As above, we don't actually do anything here except change blockState.
  */
 void
 ReleaseSavepoint(List *options)
@@ -2455,13 +2646,13 @@ ReleaseSavepoint(List *options)
 	ListCell   *cell;
 	char	   *name = NULL;
 
-	/*
-	 * Check valid block state transaction status.
-	 */
 	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")));
@@ -2474,19 +2665,21 @@ ReleaseSavepoint(List *options)
 		case TBLOCK_SUBINPROGRESS:
 			break;
 
-			/* these cases are invalid. */
+			/* These cases are invalid. */
 		case TBLOCK_DEFAULT:
 		case TBLOCK_STARTED:
 		case TBLOCK_BEGIN:
-		case TBLOCK_ENDABORT:
-		case TBLOCK_END:
-		case TBLOCK_SUBABORT:
 		case TBLOCK_SUBBEGIN:
+		case TBLOCK_END:
 		case TBLOCK_SUBEND:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT:
+		case TBLOCK_SUBABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "ReleaseSavepoint: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2539,6 +2732,8 @@ ReleaseSavepoint(List *options)
 /*
  * RollbackToSavepoint
  *		This executes a ROLLBACK TO <savepoint> command.
+ *
+ * As above, we don't actually do anything here except change blockState.
  */
 void
 RollbackToSavepoint(List *options)
@@ -2552,11 +2747,11 @@ RollbackToSavepoint(List *options)
 	switch (s->blockState)
 	{
 			/*
-			 * We can't rollback to a savepoint if there is no saveopint
+			 * We can't rollback to a savepoint if there is no savepoint
 			 * defined.
 			 */
-		case TBLOCK_ABORT:
 		case TBLOCK_INPROGRESS:
+		case TBLOCK_ABORT:
 			ereport(ERROR,
 					(errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
 					 errmsg("no such savepoint")));
@@ -2565,27 +2760,23 @@ RollbackToSavepoint(List *options)
 			/*
 			 * There is at least one savepoint, so proceed.
 			 */
-		case TBLOCK_SUBABORT:
 		case TBLOCK_SUBINPROGRESS:
-
-			/*
-			 * Have to do AbortSubTransaction, but first check if this is
-			 * the right subtransaction
-			 */
+		case TBLOCK_SUBABORT:
 			break;
 
-			/* these cases are invalid. */
+			/* These cases are invalid. */
 		case TBLOCK_DEFAULT:
 		case TBLOCK_STARTED:
 		case TBLOCK_BEGIN:
+		case TBLOCK_SUBBEGIN:
 		case TBLOCK_END:
-		case TBLOCK_ENDABORT:
 		case TBLOCK_SUBEND:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
-		case TBLOCK_SUBBEGIN:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "RollbackToSavepoint: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2619,27 +2810,34 @@ RollbackToSavepoint(List *options)
 				 errmsg("no such savepoint")));
 
 	/*
-	 * Abort the current subtransaction, if needed.  We can't Cleanup the
-	 * savepoint yet, so signal CommitTransactionCommand to do it and
-	 * close all savepoints up to the target level.
-	 */
-	if (s->blockState == TBLOCK_SUBINPROGRESS)
-		AbortSubTransaction();
-	s->blockState = TBLOCK_SUBENDABORT;
-
-	/*
 	 * Mark "abort pending" all subtransactions up to the target
-	 * subtransaction.	(Except the current subtransaction!)
+	 * subtransaction.	The actual aborts will happen when control gets
+	 * to CommitTransactionCommand.
 	 */
 	xact = CurrentTransactionState;
-
-	while (xact != target)
+	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));
-		Assert(xact->blockState == TBLOCK_SUBINPROGRESS);
-		xact->blockState = TBLOCK_SUBABORT_PENDING;
 	}
+
+	/* 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));
 }
 
 /*
@@ -2649,8 +2847,6 @@ RollbackToSavepoint(List *options)
  *		be called when not inside a BEGIN block.  Also, we automatically
  *		cycle through CommitTransactionCommand/StartTransactionCommand
  *		instead of expecting the caller to do it.
- *
- * Optionally, name can be NULL to create an unnamed savepoint.
  */
 void
 BeginInternalSubTransaction(char *name)
@@ -2667,28 +2863,27 @@ BeginInternalSubTransaction(char *name)
 			s = CurrentTransactionState;		/* changed by push */
 
 			/*
-			 * Note that we are allocating the savepoint name in the
-			 * parent transaction's CurTransactionContext, since we don't
-			 * yet have a transaction context for the new guy.
+			 * Savepoint names, like the TransactionState block itself,
+			 * live in TopTransactionContext.
 			 */
 			if (name)
-				s->name = MemoryContextStrdup(CurTransactionContext, name);
-			s->blockState = TBLOCK_SUBBEGIN;
+				s->name = MemoryContextStrdup(TopTransactionContext, name);
 			break;
 
-			/* These cases are invalid.  Reject them altogether. */
+			/* 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_ENDABORT:
-		case TBLOCK_END:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
-		case TBLOCK_SUBEND:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "BeginInternalSubTransaction: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2716,7 +2911,6 @@ ReleaseCurrentSubTransaction(void)
 	Assert(s->state == TRANS_INPROGRESS);
 	MemoryContextSwitchTo(CurTransactionContext);
 	CommitSubTransaction();
-	PopTransaction();
 	s = CurrentTransactionState; /* changed by pop */
 	Assert(s->state == TRANS_INPROGRESS);
 }
@@ -2736,24 +2930,25 @@ RollbackAndReleaseCurrentSubTransaction(void)
 	switch (s->blockState)
 	{
 			/* Must be in a subtransaction */
-		case TBLOCK_SUBABORT:
 		case TBLOCK_SUBINPROGRESS:
+		case TBLOCK_SUBABORT:
 			break;
 
-			/* these cases are invalid. */
+			/* These cases are invalid. */
 		case TBLOCK_DEFAULT:
 		case TBLOCK_STARTED:
-		case TBLOCK_ABORT:
-		case TBLOCK_INPROGRESS:
 		case TBLOCK_BEGIN:
+		case TBLOCK_SUBBEGIN:
+		case TBLOCK_INPROGRESS:
 		case TBLOCK_END:
-		case TBLOCK_ENDABORT:
 		case TBLOCK_SUBEND:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
-		case TBLOCK_SUBBEGIN:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			elog(FATAL, "RollbackAndReleaseCurrentSubTransaction: unexpected state %s",
 				 BlockStateAsString(s->blockState));
 			break;
@@ -2764,10 +2959,14 @@ RollbackAndReleaseCurrentSubTransaction(void)
 	 */
 	if (s->blockState == TBLOCK_SUBINPROGRESS)
 		AbortSubTransaction();
-	s->blockState = TBLOCK_SUBENDABORT_RELEASE;
 
 	/* And clean it up, too */
-	CleanupAbortedSubTransactions(false);
+	CleanupSubTransaction();
+
+	s = CurrentTransactionState;	/* changed by pop */
+	AssertState(s->blockState == TBLOCK_SUBINPROGRESS ||
+				s->blockState == TBLOCK_INPROGRESS ||
+				s->blockState == TBLOCK_STARTED);
 }
 
 /*
@@ -2796,46 +2995,38 @@ AbortOutOfAnyTransaction(void)
 			case TBLOCK_BEGIN:
 			case TBLOCK_INPROGRESS:
 			case TBLOCK_END:
+			case TBLOCK_ABORT_PENDING:
 				/* In a transaction, so clean up */
 				AbortTransaction();
 				CleanupTransaction();
 				s->blockState = TBLOCK_DEFAULT;
 				break;
 			case TBLOCK_ABORT:
-			case TBLOCK_ENDABORT:
+			case TBLOCK_ABORT_END:
 				/* AbortTransaction already done, still need Cleanup */
 				CleanupTransaction();
 				s->blockState = TBLOCK_DEFAULT;
 				break;
-			case TBLOCK_SUBBEGIN:
 
 				/*
-				 * We didn't get as far as starting the subxact, so
-				 * there's nothing to abort.  Just pop back to parent.
+				 * In a subtransaction, so clean it up and abort parent
+				 * too
 				 */
-				PopTransaction();
-				s = CurrentTransactionState;	/* changed by pop */
-				break;
+			case TBLOCK_SUBBEGIN:
 			case TBLOCK_SUBINPROGRESS:
 			case TBLOCK_SUBEND:
 			case TBLOCK_SUBABORT_PENDING:
-
-				/*
-				 * In a subtransaction, so clean it up and abort parent
-				 * too
-				 */
+			case TBLOCK_SUBRESTART:
 				AbortSubTransaction();
 				CleanupSubTransaction();
-				PopTransaction();
 				s = CurrentTransactionState;	/* changed by pop */
 				break;
+
 			case TBLOCK_SUBABORT:
-			case TBLOCK_SUBENDABORT_ALL:
-			case TBLOCK_SUBENDABORT:
-			case TBLOCK_SUBENDABORT_RELEASE:
+			case TBLOCK_SUBABORT_END:
+			case TBLOCK_SUBABORT_RESTART:
 				/* As above, but AbortSubTransaction already done */
 				CleanupSubTransaction();
-				PopTransaction();
 				s = CurrentTransactionState;	/* changed by pop */
 				break;
 		}
@@ -2891,19 +3082,20 @@ TransactionBlockStatusCode(void)
 		case TBLOCK_STARTED:
 			return 'I';			/* idle --- not in transaction */
 		case TBLOCK_BEGIN:
+		case TBLOCK_SUBBEGIN:
 		case TBLOCK_INPROGRESS:
-		case TBLOCK_END:
 		case TBLOCK_SUBINPROGRESS:
-		case TBLOCK_SUBBEGIN:
+		case TBLOCK_END:
 		case TBLOCK_SUBEND:
 			return 'T';			/* in transaction */
 		case TBLOCK_ABORT:
-		case TBLOCK_ENDABORT:
 		case TBLOCK_SUBABORT:
-		case TBLOCK_SUBENDABORT_ALL:
-		case TBLOCK_SUBENDABORT:
+		case TBLOCK_ABORT_END:
+		case TBLOCK_SUBABORT_END:
+		case TBLOCK_ABORT_PENDING:
 		case TBLOCK_SUBABORT_PENDING:
-		case TBLOCK_SUBENDABORT_RELEASE:
+		case TBLOCK_SUBRESTART:
+		case TBLOCK_SUBABORT_RESTART:
 			return 'E';			/* in failed transaction */
 	}
 
@@ -2929,6 +3121,15 @@ IsSubTransaction(void)
 
 /*
  * 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)
@@ -2942,33 +3143,12 @@ StartSubTransaction(void)
 	s->state = TRANS_START;
 
 	/*
+	 * Initialize subsystems for new subtransaction
+	 *
 	 * must initialize resource-management stuff first
 	 */
 	AtSubStart_Memory();
 	AtSubStart_ResourceOwner();
-
-	/*
-	 * Generate a new Xid and record it in pg_subtrans.  NB: we must make
-	 * the subtrans entry BEFORE the Xid appears anywhere in shared
-	 * storage, such as in the lock table; because until it's made the Xid
-	 * may not appear to be "running" to other backends. See
-	 * GetNewTransactionId.
-	 */
-	s->transactionIdData = GetNewTransactionId(true);
-
-	SubTransSetParent(s->transactionIdData, s->parent->transactionIdData);
-
-	XactLockTableInsert(s->transactionIdData);
-
-	/*
-	 * Finish setup of other transaction state fields.
-	 */
-	s->currentUser = GetUserId();
-	s->prevXactReadOnly = XactReadOnly;
-
-	/*
-	 * Initialize other subsystems for new subtransaction
-	 */
 	AtSubStart_Inval();
 	AtSubStart_Notify();
 	AfterTriggerBeginSubXact();
@@ -2978,13 +3158,17 @@ StartSubTransaction(void)
 	/*
 	 * Call start-of-subxact callbacks
 	 */
-	CallXactCallbacks(XACT_EVENT_START_SUB, s->parent->transactionIdData);
+	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)
@@ -3005,28 +3189,42 @@ CommitSubTransaction(void)
 	CommandCounterIncrement();
 
 	/* Mark subtransaction as subcommitted */
-	RecordSubTransactionCommit();
-	AtSubCommit_childXids();
+	if (TransactionIdIsValid(s->transactionId))
+	{
+		RecordSubTransactionCommit();
+		AtSubCommit_childXids();
+	}
 
 	/* Post-commit cleanup */
 	AfterTriggerEndSubXact(true);
-	AtSubCommit_Portals(s->parent->transactionIdData,
+	AtSubCommit_Portals(s->subTransactionId,
+						s->parent->subTransactionId,
 						s->parent->curTransactionOwner);
-	AtEOSubXact_LargeObject(true, s->transactionIdData,
-							s->parent->transactionIdData);
+	AtEOSubXact_LargeObject(true, s->subTransactionId,
+							s->parent->subTransactionId);
 	AtSubCommit_Notify();
-	AtEOSubXact_UpdatePasswordFile(true, s->transactionIdData,
-								   s->parent->transactionIdData);
+	AtEOSubXact_UpdatePasswordFile(true, s->subTransactionId,
+								   s->parent->subTransactionId);
 
-	CallXactCallbacks(XACT_EVENT_COMMIT_SUB, s->parent->transactionIdData);
+	CallSubXactCallbacks(SUBXACT_EVENT_COMMIT_SUB, s->subTransactionId,
+						 s->parent->subTransactionId);
 
 	ResourceOwnerRelease(s->curTransactionOwner,
 						 RESOURCE_RELEASE_BEFORE_LOCKS,
 						 true, false);
-	AtEOSubXact_RelationCache(true, s->transactionIdData,
-							  s->parent->transactionIdData);
+	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);
@@ -3035,13 +3233,13 @@ CommitSubTransaction(void)
 						 true, false);
 
 	AtEOXact_GUC(true, true);
-	AtEOSubXact_SPI(true, s->transactionIdData);
-	AtEOSubXact_on_commit_actions(true, s->transactionIdData,
-								  s->parent->transactionIdData);
-	AtEOSubXact_Namespace(true, s->transactionIdData,
-						  s->parent->transactionIdData);
-	AtEOSubXact_Files(true, s->transactionIdData,
-					  s->parent->transactionIdData);
+	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);
 
 	/*
 	 * We need to restore the upper transaction's read-only state, in case
@@ -3058,6 +3256,8 @@ CommitSubTransaction(void)
 	AtSubCommit_Memory();
 
 	s->state = TRANS_DEFAULT;
+
+	PopTransaction();
 }
 
 /*
@@ -3099,43 +3299,53 @@ AbortSubTransaction(void)
 	 */
 	AtSubAbort_Memory();
 
-	AfterTriggerEndSubXact(false);
-	AtSubAbort_Portals(s->parent->transactionIdData,
-					   s->parent->curTransactionOwner);
-	AtEOSubXact_LargeObject(false, s->transactionIdData,
-							s->parent->transactionIdData);
-	AtSubAbort_Notify();
-	AtEOSubXact_UpdatePasswordFile(false, s->transactionIdData,
-								   s->parent->transactionIdData);
-
-	/* Advertise the fact that we aborted in pg_clog. */
-	RecordSubTransactionAbort();
-
-	/* Post-abort cleanup */
-	CallXactCallbacks(XACT_EVENT_ABORT_SUB, s->parent->transactionIdData);
-
-	ResourceOwnerRelease(s->curTransactionOwner,
-						 RESOURCE_RELEASE_BEFORE_LOCKS,
-						 false, false);
-	AtEOSubXact_RelationCache(false, s->transactionIdData,
-							  s->parent->transactionIdData);
-	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->transactionIdData);
-	AtEOSubXact_on_commit_actions(false, s->transactionIdData,
-								  s->parent->transactionIdData);
-	AtEOSubXact_Namespace(false, s->transactionIdData,
-						  s->parent->transactionIdData);
-	AtEOSubXact_Files(false, s->transactionIdData,
-					  s->parent->transactionIdData);
+	/*
+	 * 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_UpdatePasswordFile(false, s->subTransactionId,
+									   s->parent->subTransactionId);
+
+		/* Advertise the fact that we aborted in pg_clog. */
+		if (TransactionIdIsValid(s->transactionId))
+			RecordSubTransactionAbort();
+
+		/* 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);
+	}
 
 	/*
 	 * Reset user id which might have been changed transiently.  Here we
@@ -3165,6 +3375,9 @@ AbortSubTransaction(void)
 
 /*
  * 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)
@@ -3177,67 +3390,24 @@ CleanupSubTransaction(void)
 		elog(WARNING, "CleanupSubTransaction while in %s state",
 			 TransStateAsString(s->state));
 
-	AtSubCleanup_Portals();
+	AtSubCleanup_Portals(s->subTransactionId);
 
 	CurrentResourceOwner = s->parent->curTransactionOwner;
 	CurTransactionResourceOwner = s->parent->curTransactionOwner;
-	ResourceOwnerDelete(s->curTransactionOwner);
+	if (s->curTransactionOwner)
+		ResourceOwnerDelete(s->curTransactionOwner);
 	s->curTransactionOwner = NULL;
 
 	AtSubCleanup_Memory();
 
 	s->state = TRANS_DEFAULT;
-}
-
-/*
- * StartAbortedSubTransaction
- *
- * This function is used to start a subtransaction and put it immediately
- * into aborted state.	The end result should be equivalent to
- * StartSubTransaction immediately followed by AbortSubTransaction.
- * The reason we don't implement it just that way is that many of the backend
- * modules aren't designed to handle starting a subtransaction when not
- * inside a valid transaction.	Rather than making them all capable of
- * doing that, we just omit the paired start and abort calls in this path.
- */
-static void
-StartAbortedSubTransaction(void)
-{
-	TransactionState s = CurrentTransactionState;
 
-	if (s->state != TRANS_DEFAULT)
-		elog(WARNING, "StartAbortedSubTransaction while in %s state",
-			 TransStateAsString(s->state));
-
-	s->state = TRANS_START;
-
-	/*
-	 * We don't bother to generate a new Xid, so the end state is not
-	 * *exactly* like we had done a full Start/AbortSubTransaction...
-	 */
-	s->transactionIdData = InvalidTransactionId;
-
-	/* Make sure currentUser is reasonably valid */
-	Assert(s->parent != NULL);
-	s->currentUser = s->parent->currentUser;
-
-	/*
-	 * Initialize only what has to be there for CleanupSubTransaction to
-	 * work.
-	 */
-	AtSubStart_Memory();
-	AtSubStart_ResourceOwner();
-
-	s->state = TRANS_ABORT;
-
-	AtSubAbort_Memory();
-
-	ShowTransactionState("StartAbortedSubTransaction");
+	PopTransaction();
 }
 
 /*
  * PushTransaction
- *		Set up transaction state for a subtransaction
+ *		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.
@@ -3247,6 +3417,13 @@ PushTransaction(void)
 {
 	TransactionState p = CurrentTransactionState;
 	TransactionState s;
+	AclId	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.
@@ -3254,25 +3431,40 @@ PushTransaction(void)
 	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;
 
-	/* Command IDs count in a continuous sequence through subtransactions */
-	s->commandId = p->commandId;
+	CurrentTransactionState = s;
 
 	/*
-	 * Copy down some other data so that we will have valid state until
-	 * StartSubTransaction runs.
+	 * 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.
 	 */
-	s->transactionIdData = p->transactionIdData;
-	s->curTransactionContext = p->curTransactionContext;
-	s->curTransactionOwner = p->curTransactionOwner;
-	s->currentUser = p->currentUser;
-
-	CurrentTransactionState = s;
 }
 
 /*
@@ -3294,9 +3486,6 @@ PopTransaction(void)
 	if (s->parent == NULL)
 		elog(FATAL, "PopTransaction with no parent");
 
-	/* Command IDs count in a continuous sequence through subtransactions */
-	s->parent->commandId = s->commandId;
-
 	CurrentTransactionState = s->parent;
 
 	/* Let's just make sure CurTransactionContext is good */
@@ -3340,12 +3529,13 @@ ShowTransactionStateRec(TransactionState s)
 
 	/* use ereport to suppress computation if msg will not be printed */
 	ereport(DEBUG2,
-			(errmsg_internal("name: %s; blockState: %13s; state: %7s, xid/cid: %u/%02u, nestlvl: %d, children: %s",
+			(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->transactionIdData,
-							 (unsigned int) s->commandId,
+							 (unsigned int) s->transactionId,
+							 (unsigned int) s->subTransactionId,
+							 (unsigned int) currentCommandId,
 							 s->nestingLevel,
 							 nodeToString(s->childXids))));
 }
@@ -3371,8 +3561,10 @@ BlockStateAsString(TBlockState blockState)
 			return "END";
 		case TBLOCK_ABORT:
 			return "ABORT";
-		case TBLOCK_ENDABORT:
-			return "ENDABORT";
+		case TBLOCK_ABORT_END:
+			return "ABORT END";
+		case TBLOCK_ABORT_PENDING:
+			return "ABORT PEND";
 		case TBLOCK_SUBBEGIN:
 			return "SUB BEGIN";
 		case TBLOCK_SUBINPROGRESS:
@@ -3381,14 +3573,14 @@ BlockStateAsString(TBlockState blockState)
 			return "SUB END";
 		case TBLOCK_SUBABORT:
 			return "SUB ABORT";
-		case TBLOCK_SUBENDABORT_ALL:
-			return "SUB ENDAB ALL";
-		case TBLOCK_SUBENDABORT:
-			return "SUB ENDAB";
+		case TBLOCK_SUBABORT_END:
+			return "SUB ABORT END";
 		case TBLOCK_SUBABORT_PENDING:
 			return "SUB ABRT PEND";
-		case TBLOCK_SUBENDABORT_RELEASE:
-			return "SUB ENDAB REL";
+		case TBLOCK_SUBRESTART:
+			return "SUB RESTART";
+		case TBLOCK_SUBABORT_RESTART:
+			return "SUB AB RESTRT";
 	}
 	return "UNRECOGNIZED";
 }
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 0e27ba319a1..d46a3e543d8 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.169 2004/09/06 03:04:27 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.170 2004/09/16 16:58:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -747,7 +747,7 @@ begin:;
 	/* Insert record header */
 
 	record->xl_prev = Insert->PrevRecord;
-	record->xl_xid = GetCurrentTransactionId();
+	record->xl_xid = GetCurrentTransactionIdIfAny();
 	record->xl_len = len;		/* doesn't include backup blocks */
 	record->xl_info = info;
 	record->xl_rmid = rmid;