From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 9 Feb 2007 03:35:35 +0000 (+0000)
Subject: Combine cmin and cmax fields of HeapTupleHeaders into a single field, by
X-Git-Tag: REL8_3_BETA1~1269
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=c398300330cb3060d50652800dbd12729ab9f5ef;p=postgresql

Combine cmin and cmax fields of HeapTupleHeaders into a single field, by
keeping private state in each backend that has inserted and deleted the same
tuple during its current top-level transaction.  This is sufficient since
there is no need to be able to determine the cmin/cmax from any other
transaction.  This gets us back down to 23-byte headers, removing a penalty
paid in 8.0 to support subtransactions.  Patch by Heikki Linnakangas, with
minor revisions by moi, following a design hashed out awhile back on the
pghackers list.
---

diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c
index 6200f953eb..470f48777d 100644
--- a/src/backend/access/common/heaptuple.c
+++ b/src/backend/access/common/heaptuple.c
@@ -16,7 +16,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/common/heaptuple.c,v 1.114 2007/01/09 22:00:59 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/common/heaptuple.c,v 1.115 2007/02/09 03:35:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -582,14 +582,18 @@ heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
 		case MinTransactionIdAttributeNumber:
 			result = TransactionIdGetDatum(HeapTupleHeaderGetXmin(tup->t_data));
 			break;
-		case MinCommandIdAttributeNumber:
-			result = CommandIdGetDatum(HeapTupleHeaderGetCmin(tup->t_data));
-			break;
 		case MaxTransactionIdAttributeNumber:
 			result = TransactionIdGetDatum(HeapTupleHeaderGetXmax(tup->t_data));
 			break;
+		case MinCommandIdAttributeNumber:
 		case MaxCommandIdAttributeNumber:
-			result = CommandIdGetDatum(HeapTupleHeaderGetCmax(tup->t_data));
+			/*
+			 * cmin and cmax are now both aliases for the same field,
+			 * which can in fact also be a combo command id.  XXX perhaps we
+			 * should return the "real" cmin or cmax if possible, that is
+			 * if we are inside the originating transaction?
+			 */
+			result = CommandIdGetDatum(HeapTupleHeaderGetRawCommandId(tup->t_data));
 			break;
 		case TableOidAttributeNumber:
 			result = ObjectIdGetDatum(tup->t_tableOid);
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 71ba6d2e52..d46308863f 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.227 2007/02/05 04:22:18 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.228 2007/02/09 03:35:33 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1407,8 +1407,7 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
 	tup->t_data->t_infomask |= HEAP_XMAX_INVALID;
 	HeapTupleHeaderSetXmin(tup->t_data, xid);
 	HeapTupleHeaderSetCmin(tup->t_data, cid);
-	HeapTupleHeaderSetXmax(tup->t_data, 0);		/* zero out Datum fields */
-	HeapTupleHeaderSetCmax(tup->t_data, 0);		/* for cleanliness */
+	HeapTupleHeaderSetXmax(tup->t_data, 0);		/* for cleanliness */
 	tup->t_tableOid = RelationGetRelid(relation);
 
 	/*
@@ -1585,6 +1584,7 @@ heap_delete(Relation relation, ItemPointer tid,
 	PageHeader	dp;
 	Buffer		buffer;
 	bool		have_tuple_lock = false;
+	bool		iscombo;
 
 	Assert(ItemPointerIsValid(tid));
 
@@ -1724,6 +1724,9 @@ l1:
 		return result;
 	}
 
+	/* replace cid with a combo cid if necessary */
+	HeapTupleHeaderAdjustCmax(tp.t_data, &cid, &iscombo);
+
 	START_CRIT_SECTION();
 
 	/* store transaction information of xact deleting the tuple */
@@ -1733,7 +1736,7 @@ l1:
 							   HEAP_IS_LOCKED |
 							   HEAP_MOVED);
 	HeapTupleHeaderSetXmax(tp.t_data, xid);
-	HeapTupleHeaderSetCmax(tp.t_data, cid);
+	HeapTupleHeaderSetCmax(tp.t_data, cid, iscombo);
 	/* Make sure there is no forward chain link in t_ctid */
 	tp.t_data->t_ctid = tp.t_self;
 
@@ -1893,6 +1896,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	Size		newtupsize,
 				pagefree;
 	bool		have_tuple_lock = false;
+	bool		iscombo;
 
 	Assert(ItemPointerIsValid(otid));
 
@@ -2058,8 +2062,13 @@ l2:
 	newtup->t_data->t_infomask |= (HEAP_XMAX_INVALID | HEAP_UPDATED);
 	HeapTupleHeaderSetXmin(newtup->t_data, xid);
 	HeapTupleHeaderSetCmin(newtup->t_data, cid);
-	HeapTupleHeaderSetXmax(newtup->t_data, 0);	/* zero out Datum fields */
-	HeapTupleHeaderSetCmax(newtup->t_data, 0);	/* for cleanliness */
+	HeapTupleHeaderSetXmax(newtup->t_data, 0);	/* for cleanliness */
+
+	/*
+	 * Replace cid with a combo cid if necessary.  Note that we already put
+	 * the plain cid into the new tuple.
+	 */
+	HeapTupleHeaderAdjustCmax(oldtup.t_data, &cid, &iscombo);
 
 	/*
 	 * If the toaster needs to be activated, OR if the new tuple will not fit
@@ -2088,7 +2097,7 @@ l2:
 									   HEAP_IS_LOCKED |
 									   HEAP_MOVED);
 		HeapTupleHeaderSetXmax(oldtup.t_data, xid);
-		HeapTupleHeaderSetCmax(oldtup.t_data, cid);
+		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
 		/* temporarily make it look not-updated */
 		oldtup.t_data->t_ctid = oldtup.t_self;
 		already_marked = true;
@@ -2183,7 +2192,7 @@ l2:
 									   HEAP_IS_LOCKED |
 									   HEAP_MOVED);
 		HeapTupleHeaderSetXmax(oldtup.t_data, xid);
-		HeapTupleHeaderSetCmax(oldtup.t_data, cid);
+		HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
 	}
 
 	/* record address of new tuple in t_ctid of old one */
@@ -2687,12 +2696,11 @@ l3:
 	/*
 	 * Store transaction information of xact locking the tuple.
 	 *
-	 * Note: our CID is meaningless if storing a MultiXactId, but no harm in
-	 * storing it anyway.
+	 * Note: Cmax is meaningless in this context, so don't set it; this
+	 * avoids possibly generating a useless combo CID.
 	 */
 	tuple->t_data->t_infomask = new_infomask;
 	HeapTupleHeaderSetXmax(tuple->t_data, xid);
-	HeapTupleHeaderSetCmax(tuple->t_data, cid);
 	/* Make sure there is no forward chain link in t_ctid */
 	tuple->t_data->t_ctid = *tid;
 
@@ -3443,7 +3451,7 @@ heap_xlog_delete(XLogRecPtr lsn, XLogRecord *record)
 						  HEAP_IS_LOCKED |
 						  HEAP_MOVED);
 	HeapTupleHeaderSetXmax(htup, record->xl_xid);
-	HeapTupleHeaderSetCmax(htup, FirstCommandId);
+	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
 	/* Make sure there is no forward chain link in t_ctid */
 	htup->t_ctid = xlrec->target.tid;
 	PageSetLSN(page, lsn);
@@ -3608,7 +3616,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool move)
 							  HEAP_IS_LOCKED |
 							  HEAP_MOVED);
 		HeapTupleHeaderSetXmax(htup, record->xl_xid);
-		HeapTupleHeaderSetCmax(htup, FirstCommandId);
+		HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
 		/* Set forward chain link in t_ctid */
 		htup->t_ctid = xlrec->newtid;
 	}
@@ -3761,7 +3769,7 @@ heap_xlog_lock(XLogRecPtr lsn, XLogRecord *record)
 	else
 		htup->t_infomask |= HEAP_XMAX_EXCL_LOCK;
 	HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
-	HeapTupleHeaderSetCmax(htup, FirstCommandId);
+	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
 	/* Make sure there is no forward chain link in t_ctid */
 	htup->t_ctid = xlrec->target.tid;
 	PageSetLSN(page, lsn);
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 26a3c5ddc2..ab8b5fd8b4 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 1.233 2007/02/07 23:11:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.234 2007/02/09 03:35:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -38,11 +38,12 @@
 #include "storage/lmgr.h"
 #include "storage/procarray.h"
 #include "storage/smgr.h"
+#include "utils/combocid.h"
 #include "utils/flatfiles.h"
+#include "utils/guc.h"
 #include "utils/inval.h"
 #include "utils/memutils.h"
 #include "utils/relcache.h"
-#include "utils/guc.h"
 
 
 /*
@@ -1628,6 +1629,7 @@ CommitTransaction(void)
 	AtEOXact_Namespace(true);
 	/* smgrcommit already done */
 	AtEOXact_Files();
+	AtEOXact_ComboCid();
 	pgstat_clear_snapshot();
 	pgstat_count_xact_commit();
 	pgstat_report_txn_timestamp(0);
@@ -1845,6 +1847,7 @@ PrepareTransaction(void)
 	AtEOXact_Namespace(true);
 	/* smgrcommit already done */
 	AtEOXact_Files();
+	AtEOXact_ComboCid();
 	pgstat_clear_snapshot();
 
 	CurrentResourceOwner = NULL;
@@ -1997,6 +2000,7 @@ AbortTransaction(void)
 	AtEOXact_Namespace(false);
 	smgrabort();
 	AtEOXact_Files();
+	AtEOXact_ComboCid();
 	pgstat_clear_snapshot();
 	pgstat_count_xact_rollback();
 	pgstat_report_txn_timestamp(0);
diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index 886883a6ae..c36d9fee13 100644
--- a/src/backend/utils/fmgr/fmgr.c
+++ b/src/backend/utils/fmgr/fmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/fmgr.c,v 1.103 2007/01/05 22:19:43 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/fmgr.c,v 1.104 2007/02/09 03:35:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -64,7 +64,7 @@ typedef struct
 	/* fn_oid is the hash key and so must be first! */
 	Oid			fn_oid;			/* OID of an external C function */
 	TransactionId fn_xmin;		/* for checking up-to-dateness */
-	CommandId	fn_cmin;
+	ItemPointerData	fn_tid;
 	PGFunction	user_fn;		/* the function's address */
 	const Pg_finfo_record *inforec;		/* address of its info record */
 } CFuncHashTabEntry;
@@ -483,7 +483,7 @@ lookup_C_func(HeapTuple procedureTuple)
 	if (entry == NULL)
 		return NULL;			/* no such entry */
 	if (entry->fn_xmin == HeapTupleHeaderGetXmin(procedureTuple->t_data) &&
-		entry->fn_cmin == HeapTupleHeaderGetCmin(procedureTuple->t_data))
+		ItemPointerEquals(&entry->fn_tid, &procedureTuple->t_self))
 		return entry;			/* OK */
 	return NULL;				/* entry is out of date */
 }
@@ -521,7 +521,7 @@ record_C_func(HeapTuple procedureTuple,
 					&found);
 	/* OID is already filled in */
 	entry->fn_xmin = HeapTupleHeaderGetXmin(procedureTuple->t_data);
-	entry->fn_cmin = HeapTupleHeaderGetCmin(procedureTuple->t_data);
+	entry->fn_tid = procedureTuple->t_self;
 	entry->user_fn = user_fn;
 	entry->inforec = inforec;
 }
diff --git a/src/backend/utils/time/Makefile b/src/backend/utils/time/Makefile
index 67d2bfd262..9cbe31f8a6 100644
--- a/src/backend/utils/time/Makefile
+++ b/src/backend/utils/time/Makefile
@@ -4,7 +4,7 @@
 #    Makefile for utils/time
 #
 # IDENTIFICATION
-#    $PostgreSQL: pgsql/src/backend/utils/time/Makefile,v 1.11 2007/01/20 17:16:15 petere Exp $
+#    $PostgreSQL: pgsql/src/backend/utils/time/Makefile,v 1.12 2007/02/09 03:35:34 tgl Exp $
 #
 #-------------------------------------------------------------------------
 
@@ -12,12 +12,12 @@ subdir = src/backend/utils/time
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = tqual.o
+OBJS = combocid.o tqual.o
 
 all: SUBSYS.o
 
 SUBSYS.o: $(OBJS)
 	$(LD) $(LDREL) $(LDOUT) SUBSYS.o $(OBJS)
 
-clean: 
+clean:
 	rm -f SUBSYS.o $(OBJS)
diff --git a/src/backend/utils/time/combocid.c b/src/backend/utils/time/combocid.c
new file mode 100644
index 0000000000..5ba76660fd
--- /dev/null
+++ b/src/backend/utils/time/combocid.c
@@ -0,0 +1,282 @@
+/*-------------------------------------------------------------------------
+ *
+ * combocid.c
+ *	  Combo command ID support routines
+ *
+ * Before version 8.3, HeapTupleHeaderData had separate fields for cmin
+ * and cmax.  To reduce the header size, cmin and cmax are now overlayed
+ * in the same field in the header.  That usually works because you rarely
+ * insert and delete a tuple in the same transaction, and we don't need
+ * either field to remain valid after the originating transaction exits.
+ * To make it work when the inserting transaction does delete the tuple,
+ * we create a "combo" command ID and store that in the tuple header
+ * instead of cmin and cmax. The combo command ID can be mapped to the
+ * real cmin and cmax using a backend-private array, which is managed by
+ * this module.
+ *
+ * To allow reusing existing combo cids, we also keep a hash table that
+ * maps cmin,cmax pairs to combo cids.  This keeps the data structure size
+ * reasonable in most cases, since the number of unique pairs used by any
+ * one transaction is likely to be small.
+ *
+ * With a 32-bit combo command id we can represent 2^32 distinct cmin,cmax
+ * combinations. In the most perverse case where each command deletes a tuple
+ * generated by every previous command, the number of combo command ids
+ * required for N commands is N*(N+1)/2.  That means that in the worst case,
+ * that's enough for 92682 commands.  In practice, you'll run out of memory
+ * and/or disk space way before you reach that limit.
+ *
+ * The array and hash table are kept in TopTransactionContext, and are
+ * destroyed at the end of each transaction.
+ *
+ *
+ * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/utils/time/combocid.c,v 1.1 2007/02/09 03:35:34 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/htup.h"
+#include "access/xact.h"
+#include "utils/combocid.h"
+#include "utils/hsearch.h"
+#include "utils/memutils.h"
+
+
+/* Hash table to lookup combo cids by cmin and cmax */
+static HTAB *comboHash = NULL;
+
+/* Key and entry structures for the hash table */
+typedef struct
+{
+	CommandId cmin;
+	CommandId cmax;
+} ComboCidKeyData;
+
+typedef ComboCidKeyData *ComboCidKey;
+
+typedef struct
+{
+	ComboCidKeyData key;
+	CommandId combocid;
+} ComboCidEntryData;
+
+typedef ComboCidEntryData *ComboCidEntry;
+
+/* Initial size of the hash table */
+#define CCID_HASH_SIZE			100
+
+
+/*
+ * An array of cmin,cmax pairs, indexed by combo command id.
+ * To convert a combo cid to cmin and cmax, you do a simple array lookup.
+ */
+static ComboCidKey comboCids = NULL;
+static int usedComboCids = 0;			/* number of elements in comboCids */
+static int sizeComboCids = 0;			/* allocated size of array */
+
+/* Initial size of the array */
+#define CCID_ARRAY_SIZE			100
+
+
+/* prototypes for internal functions */
+static CommandId GetComboCommandId(CommandId cmin, CommandId cmax);
+static CommandId GetRealCmin(CommandId combocid);
+static CommandId GetRealCmax(CommandId combocid);
+
+
+/**** External API ****/
+
+/*
+ * GetCmin and GetCmax assert that they are only called in situations where
+ * they make sense, that is, can deliver a useful answer.  If you have
+ * reason to examine a tuple's t_cid field from a transaction other than
+ * the originating one, use HeapTupleHeaderGetRawCommandId() directly.
+ */
+
+CommandId
+HeapTupleHeaderGetCmin(HeapTupleHeader tup)
+{
+	CommandId cid = HeapTupleHeaderGetRawCommandId(tup);
+
+	Assert(!(tup->t_infomask & HEAP_MOVED));
+	Assert(TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tup)));
+
+	if (tup->t_infomask & HEAP_COMBOCID)
+		return GetRealCmin(cid);
+	else
+		return cid;
+}
+
+CommandId
+HeapTupleHeaderGetCmax(HeapTupleHeader tup)
+{
+	CommandId cid = HeapTupleHeaderGetRawCommandId(tup);
+
+	/* We do not store cmax when locking a tuple */
+	Assert(!(tup->t_infomask & (HEAP_MOVED | HEAP_IS_LOCKED)));
+	Assert(TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmax(tup)));
+
+	if (tup->t_infomask & HEAP_COMBOCID)
+		return GetRealCmax(cid);
+	else
+		return cid;
+}
+
+/*
+ * Given a tuple we are about to delete, determine the correct value to store
+ * into its t_cid field.
+ *
+ * If we don't need a combo CID, *cmax is unchanged and *iscombo is set to
+ * FALSE.  If we do need one, *cmax is replaced by a combo CID and *iscombo
+ * is set to TRUE.
+ *
+ * The reason this is separate from the actual HeapTupleHeaderSetCmax()
+ * operation is that this could fail due to out-of-memory conditions.  Hence
+ * we need to do this before entering the critical section that actually
+ * changes the tuple in shared buffers.
+ */
+void
+HeapTupleHeaderAdjustCmax(HeapTupleHeader tup,
+						  CommandId *cmax,
+						  bool *iscombo)
+{
+	/*
+	 * If we're marking a tuple deleted that was inserted by (any
+	 * subtransaction of) our transaction, we need to use a combo command id.
+	 * Test for HEAP_XMIN_COMMITTED first, because it's cheaper than a
+	 * TransactionIdIsCurrentTransactionId call.
+	 */
+	if (!(tup->t_infomask & HEAP_XMIN_COMMITTED) &&
+		TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tup)))
+	{
+		CommandId cmin = HeapTupleHeaderGetRawCommandId(tup);
+
+		*cmax = GetComboCommandId(cmin, *cmax);
+		*iscombo = true;
+	}
+	else
+	{
+		*iscombo = false;
+	}
+}
+
+/*
+ * Combo command ids are only interesting to the inserting and deleting
+ * transaction, so we can forget about them at the end of transaction.
+ */
+void
+AtEOXact_ComboCid(void)
+{
+	/*
+	 * Don't bother to pfree. These are allocated in TopTransactionContext,
+	 * so they're going to go away at the end of transaction anyway.
+	 */
+	comboHash = NULL;
+
+	comboCids = NULL;
+	usedComboCids = 0;
+	sizeComboCids = 0;
+}
+
+
+/**** Internal routines ****/
+
+/*
+ * Get a combo command id that maps to cmin and cmax.
+ *
+ * We try to reuse old combo command ids when possible.
+ */
+static CommandId
+GetComboCommandId(CommandId cmin, CommandId cmax)
+{
+	CommandId combocid;
+	ComboCidKeyData key;
+	ComboCidEntry entry;
+	bool found;
+
+	/*
+	 * Create the hash table and array the first time we need to use
+	 * combo cids in the transaction.
+	 */
+	if (comboHash == NULL)
+	{
+		HASHCTL hash_ctl;
+
+		memset(&hash_ctl, 0, sizeof(hash_ctl));
+		hash_ctl.keysize = sizeof(ComboCidKeyData);
+		hash_ctl.entrysize = sizeof(ComboCidEntryData);
+		hash_ctl.hash = tag_hash;
+		hash_ctl.hcxt = TopTransactionContext;
+
+		comboHash = hash_create("Combo CIDs",
+								CCID_HASH_SIZE,
+								&hash_ctl,
+								HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);
+
+		comboCids = (ComboCidKeyData *)
+			MemoryContextAlloc(TopTransactionContext,
+							   sizeof(ComboCidKeyData) * CCID_ARRAY_SIZE);
+		sizeComboCids = CCID_ARRAY_SIZE;
+		usedComboCids = 0;
+	}
+
+	/* Lookup or create a hash entry with the desired cmin/cmax */
+
+	/* We assume there is no struct padding in ComboCidKeyData! */
+	key.cmin = cmin;
+	key.cmax = cmax;
+	entry = (ComboCidEntry) hash_search(comboHash,
+										(void *) &key,
+										HASH_ENTER,
+										&found);
+
+	if (found)
+	{
+		/* Reuse an existing combo cid */
+		return entry->combocid;
+	}
+
+	/*
+	 * We have to create a new combo cid. Check that there's room
+	 * for it in the array, and grow it if there isn't.
+	 */
+	if (usedComboCids >= sizeComboCids)
+	{
+		/* We need to grow the array */
+		int		newsize = sizeComboCids * 2;
+
+		comboCids = (ComboCidKeyData *)
+			repalloc(comboCids, sizeof(ComboCidKeyData) * newsize);
+		sizeComboCids = newsize;
+	}
+
+	combocid = usedComboCids;
+
+	comboCids[combocid].cmin = cmin;
+	comboCids[combocid].cmax = cmax;
+	usedComboCids++;
+
+	entry->combocid = combocid;
+
+	return combocid;
+}
+
+static CommandId
+GetRealCmin(CommandId combocid)
+{
+	Assert(combocid < usedComboCids);
+	return comboCids[combocid].cmin;
+}
+
+static CommandId
+GetRealCmax(CommandId combocid)
+{
+	Assert(combocid < usedComboCids);
+	return comboCids[combocid].cmax;
+}
diff --git a/src/include/access/htup.h b/src/include/access/htup.h
index eecc6959e8..31de835d29 100644
--- a/src/include/access/htup.h
+++ b/src/include/access/htup.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/htup.h,v 1.90 2007/02/05 04:22:18 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/htup.h,v 1.91 2007/02/09 03:35:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -45,7 +45,7 @@
 
 /*
  * Heap tuple header.  To avoid wasting space, the fields should be
- * layed out in such a way to avoid structure padding.
+ * laid out in such a way as to avoid structure padding.
  *
  * Datums of composite types (row types) share the same general structure
  * as on-disk tuples, so that the same routines can be used to build and
@@ -65,17 +65,18 @@
  *			object ID (if HEAP_HASOID is set in t_infomask)
  *			user data fields
  *
- * We store five "virtual" fields Xmin, Cmin, Xmax, Cmax, and Xvac in four
- * physical fields.  Xmin, Cmin and Xmax are always really stored, but
- * Cmax and Xvac share a field.  This works because we know that there are
- * only a limited number of states that a tuple can be in, and that Cmax
- * is only interesting for the lifetime of the deleting transaction.
- * This assumes that VACUUM FULL never tries to move a tuple whose Cmax
- * is still interesting (ie, delete-in-progress).
- *
- * Note that in 7.3 and 7.4 a similar idea was applied to Xmax and Cmin.
- * However, with the advent of subtransactions, a tuple may need both Xmax
- * and Cmin simultaneously, so this is no longer possible.
+ * We store five "virtual" fields Xmin, Cmin, Xmax, Cmax, and Xvac in three
+ * physical fields.  Xmin and Xmax are always really stored, but Cmin, Cmax
+ * and Xvac share a field.  This works because we know that Cmin and Cmax
+ * are only interesting for the lifetime of the inserting and deleting
+ * transaction respectively.  If a tuple is inserted and deleted in the same
+ * transaction, we store a "combo" command id that can be mapped to the real
+ * cmin and cmax, but only by use of local state within the originating
+ * backend.  See combocid.c for more details.  Meanwhile, Xvac is only set
+ * by VACUUM FULL, which does not have any command sub-structure and so does
+ * not need either Cmin or Cmax.  (This requires that VACUUM FULL never try
+ * to move a tuple whose Cmin or Cmax is still interesting, ie, an insert-
+ * in-progress or delete-in-progress tuple.)
  *
  * A word about t_ctid: whenever a new tuple is stored on disk, its t_ctid
  * is initialized with its own TID (location).	If the tuple is ever updated,
@@ -103,14 +104,13 @@
 typedef struct HeapTupleFields
 {
 	TransactionId t_xmin;		/* inserting xact ID */
-	CommandId	t_cmin;			/* inserting command ID */
 	TransactionId t_xmax;		/* deleting or locking xact ID */
 
 	union
 	{
-		CommandId	t_cmax;		/* deleting or locking command ID */
+		CommandId	t_cid;		/* inserting or deleting command ID, or both */
 		TransactionId t_xvac;	/* VACUUM FULL xact ID */
-	}			t_field4;
+	}			t_field3;
 } HeapTupleFields;
 
 typedef struct DatumTupleFields
@@ -145,7 +145,7 @@ typedef struct HeapTupleHeaderData
 
 	uint8		t_hoff;			/* sizeof header incl. bitmap, padding */
 
-	/* ^ - 27 bytes - ^ */
+	/* ^ - 23 bytes - ^ */
 
 	bits8		t_bits[1];		/* bitmap of NULLs -- VARIABLE LENGTH */
 
@@ -163,7 +163,7 @@ typedef HeapTupleHeaderData *HeapTupleHeader;
 #define HEAP_HASCOMPRESSED		0x0008	/* has compressed stored attribute(s) */
 #define HEAP_HASEXTENDED		0x000C	/* the two above combined */
 #define HEAP_HASOID				0x0010	/* has an object-id field */
-/* 0x0020 is presently unused */
+#define HEAP_COMBOCID			0x0020	/* t_cid is a combo cid */
 #define HEAP_XMAX_EXCL_LOCK		0x0040	/* xmax is exclusive locker */
 #define HEAP_XMAX_SHARED_LOCK	0x0080	/* xmax is shared locker */
 /* if either LOCK bit is set, xmax hasn't deleted the tuple, only locked it */
@@ -180,17 +180,13 @@ typedef HeapTupleHeaderData *HeapTupleHeader;
 										 * FULL */
 #define HEAP_MOVED (HEAP_MOVED_OFF | HEAP_MOVED_IN)
 
-#define HEAP_XACT_MASK			0xFFC0	/* visibility-related bits */
+#define HEAP_XACT_MASK			0xFFE0	/* visibility-related bits */
 
-/* information stored in t_infomask2, and accessor macros */
+/*
+ * information stored in t_infomask2:
+ */
 #define HEAP_NATTS_MASK			0x7FF	/* 11 bits for number of attributes */
-/* bits 0xF800 are unused */
-
-#define HeapTupleHeaderGetNatts(tup) ((tup)->t_infomask2 & HEAP_NATTS_MASK)
-#define HeapTupleHeaderSetNatts(tup, natts) \
-( \
-	(tup)->t_infomask2 = ((tup)->t_infomask2 & ~HEAP_NATTS_MASK) | (natts) \
-)
+/* bits 0xF800 are currently unused */
 
 /*
  * HeapTupleHeader accessor macros
@@ -219,39 +215,40 @@ typedef HeapTupleHeaderData *HeapTupleHeader;
 	TransactionIdStore((xid), &(tup)->t_choice.t_heap.t_xmax) \
 )
 
-#define HeapTupleHeaderGetCmin(tup) \
-( \
-	(tup)->t_choice.t_heap.t_cmin \
-)
-
-#define HeapTupleHeaderSetCmin(tup, cid) \
-( \
-	(tup)->t_choice.t_heap.t_cmin = (cid) \
-)
-
 /*
- * Note: GetCmax will produce wrong answers after SetXvac has been executed
- * by a transaction other than the inserting one.  We could check
- * HEAP_XMAX_INVALID and return FirstCommandId if it's clear, but since that
- * bit will be set again if the deleting transaction aborts, there'd be no
- * real gain in safety from the extra test.  So, just rely on the caller not
- * to trust the value unless it's meaningful.
+ * HeapTupleHeaderGetRawCommandId will give you what's in the header whether
+ * it is useful or not.  Most code should use HeapTupleHeaderGetCmin or
+ * HeapTupleHeaderGetCmax instead, but note that those Assert that you can
+ * get a legitimate result, ie you are in the originating transaction!
  */
-#define HeapTupleHeaderGetCmax(tup) \
+#define HeapTupleHeaderGetRawCommandId(tup) \
 ( \
-	(tup)->t_choice.t_heap.t_field4.t_cmax \
+	(tup)->t_choice.t_heap.t_field3.t_cid \
 )
 
-#define HeapTupleHeaderSetCmax(tup, cid) \
+/* SetCmin is reasonably simple since we never need a combo CID */
+#define HeapTupleHeaderSetCmin(tup, cid) \
 do { \
 	Assert(!((tup)->t_infomask & HEAP_MOVED)); \
-	(tup)->t_choice.t_heap.t_field4.t_cmax = (cid); \
+	(tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
+	(tup)->t_infomask &= ~HEAP_COMBOCID; \
+} while (0)
+
+/* SetCmax must be used after HeapTupleHeaderAdjustCmax; see combocid.c */
+#define HeapTupleHeaderSetCmax(tup, cid, iscombo) \
+do { \
+	Assert(!((tup)->t_infomask & HEAP_MOVED)); \
+	(tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
+	if (iscombo) \
+		(tup)->t_infomask |= HEAP_COMBOCID; \
+	else \
+		(tup)->t_infomask &= ~HEAP_COMBOCID; \
 } while (0)
 
 #define HeapTupleHeaderGetXvac(tup) \
 ( \
 	((tup)->t_infomask & HEAP_MOVED) ? \
-		(tup)->t_choice.t_heap.t_field4.t_xvac \
+		(tup)->t_choice.t_heap.t_field3.t_xvac \
 	: \
 		InvalidTransactionId \
 )
@@ -259,7 +256,7 @@ do { \
 #define HeapTupleHeaderSetXvac(tup, xid) \
 do { \
 	Assert((tup)->t_infomask & HEAP_MOVED); \
-	TransactionIdStore((xid), &(tup)->t_choice.t_heap.t_field4.t_xvac); \
+	TransactionIdStore((xid), &(tup)->t_choice.t_heap.t_field3.t_xvac); \
 } while (0)
 
 #define HeapTupleHeaderGetDatumLength(tup) \
@@ -306,6 +303,14 @@ do { \
 	*((Oid *) ((char *)(tup) + (tup)->t_hoff - sizeof(Oid))) = (oid); \
 } while (0)
 
+#define HeapTupleHeaderGetNatts(tup) \
+	((tup)->t_infomask2 & HEAP_NATTS_MASK)
+
+#define HeapTupleHeaderSetNatts(tup, natts) \
+( \
+	(tup)->t_infomask2 = ((tup)->t_infomask2 & ~HEAP_NATTS_MASK) | (natts) \
+)
+
 
 /*
  * BITMAPLEN(NATTS) -
@@ -374,9 +379,9 @@ do { \
  * and thereby prevent accidental use of the nonexistent fields.
  *
  * MinimalTupleData contains a length word, some padding, and fields matching
- * HeapTupleHeaderData beginning with t_infomask2. The padding is chosen so that
- * offsetof(t_infomask2) is the same modulo MAXIMUM_ALIGNOF in both structs.
- * This makes data alignment rules equivalent in both cases.
+ * HeapTupleHeaderData beginning with t_infomask2. The padding is chosen so
+ * that offsetof(t_infomask2) is the same modulo MAXIMUM_ALIGNOF in both
+ * structs.   This makes data alignment rules equivalent in both cases.
  *
  * When a minimal tuple is accessed via a HeapTupleData pointer, t_data is
  * set to point MINIMAL_TUPLE_OFFSET bytes before the actual start of the
@@ -405,7 +410,7 @@ typedef struct MinimalTupleData
 
 	uint8		t_hoff;			/* sizeof header incl. bitmap, padding */
 
-	/* ^ - 27 bytes - ^ */
+	/* ^ - 23 bytes - ^ */
 
 	bits8		t_bits[1];		/* bitmap of NULLs -- VARIABLE LENGTH */
 
@@ -638,4 +643,11 @@ typedef struct xl_heap_freeze
 
 #define SizeOfHeapFreeze (offsetof(xl_heap_freeze, cutoff_xid) + sizeof(TransactionId))
 
+/* HeapTupleHeader functions implemented in utils/time/combocid.c */
+extern CommandId HeapTupleHeaderGetCmin(HeapTupleHeader tup);
+extern CommandId HeapTupleHeaderGetCmax(HeapTupleHeader tup);
+extern void HeapTupleHeaderAdjustCmax(HeapTupleHeader tup,
+									  CommandId *cmax,
+									  bool *iscombo);
+
 #endif   /* HTUP_H */
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 9ebc4e9b9f..5bdda05960 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -37,7 +37,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.382 2007/02/07 23:11:29 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.383 2007/02/09 03:35:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	200702071
+#define CATALOG_VERSION_NO	200702081
 
 #endif
diff --git a/src/include/storage/bufpage.h b/src/include/storage/bufpage.h
index 53ce47f068..abb51404a5 100644
--- a/src/include/storage/bufpage.h
+++ b/src/include/storage/bufpage.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.69 2007/01/05 22:19:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.70 2007/02/09 03:35:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -132,10 +132,11 @@ typedef PageHeaderData *PageHeader;
 /*
  * Page layout version number 0 is for pre-7.3 Postgres releases.
  * Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout.
- * Release 8.0 changed the HeapTupleHeader layout again.
- * Release 8.1 redefined HeapTupleHeader infomask bits.
+ * Release 8.0 uses 2; it changed the HeapTupleHeader layout again.
+ * Release 8.1 uses 3; it redefined HeapTupleHeader infomask bits.
+ * Release 8.3 uses 4; it changed the HeapTupleHeader layout again.
  */
-#define PG_PAGE_LAYOUT_VERSION		3
+#define PG_PAGE_LAYOUT_VERSION		4
 
 
 /* ----------------------------------------------------------------
diff --git a/src/include/utils/combocid.h b/src/include/utils/combocid.h
new file mode 100644
index 0000000000..b9497a68a5
--- /dev/null
+++ b/src/include/utils/combocid.h
@@ -0,0 +1,25 @@
+/*-------------------------------------------------------------------------
+ *
+ * combocid.h
+ *	  Combo command ID support routines
+ *
+ *
+ * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $PostgreSQL: pgsql/src/include/utils/combocid.h,v 1.1 2007/02/09 03:35:34 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef COMBOCID_H
+#define COMBOCID_H
+
+/*
+ * HeapTupleHeaderGetCmin and HeapTupleHeaderGetCmax function prototypes
+ * are in access/htup.h, because that's where the macro definitions that
+ * those functions replaced used to be.
+ */
+
+extern void AtEOXact_ComboCid(void);
+
+#endif   /* COMBOCID_H */
diff --git a/src/pl/plperl/plperl.c b/src/pl/plperl/plperl.c
index 0cf8c57a13..33027c53bd 100644
--- a/src/pl/plperl/plperl.c
+++ b/src/pl/plperl/plperl.c
@@ -1,7 +1,7 @@
 /**********************************************************************
  * plperl.c - perl as a procedural language for PostgreSQL
  *
- *	  $PostgreSQL: pgsql/src/pl/plperl/plperl.c,v 1.126 2007/02/01 19:10:29 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plperl/plperl.c,v 1.127 2007/02/09 03:35:34 tgl Exp $
  *
  **********************************************************************/
 
@@ -41,7 +41,7 @@ typedef struct plperl_proc_desc
 {
 	char	   *proname;
 	TransactionId fn_xmin;
-	CommandId	fn_cmin;
+	ItemPointerData fn_tid;
 	bool		fn_readonly;
 	bool		lanpltrusted;
 	bool		fn_retistuple;	/* true, if function returns tuple */
@@ -296,7 +296,7 @@ _PG_init(void)
  *
  * We start out by creating a "held" interpreter that we can use in
  * trusted or untrusted mode (but not both) as the need arises. Later, we
- * assign that interpreter if it is available to either the trusted or 
+ * assign that interpreter if it is available to either the trusted or
  * untrusted interpreter. If it has already been assigned, and we need to
  * create the other interpreter, we do that if we can, or error out.
  * We detect if it is safe to run two interpreters during the setup of the
@@ -304,7 +304,7 @@ _PG_init(void)
  */
 
 
-static void 
+static void
 check_interp(bool trusted)
 {
 	if (interp_state == INTERP_HELD)
@@ -322,7 +322,7 @@ check_interp(bool trusted)
 		plperl_held_interp = NULL;
 		trusted_context = trusted;
 	}
-	else if (interp_state == INTERP_BOTH || 
+	else if (interp_state == INTERP_BOTH ||
 			 (trusted && interp_state == INTERP_TRUSTED) ||
 			 (!trusted && interp_state == INTERP_UNTRUSTED))
 	{
@@ -349,11 +349,9 @@ check_interp(bool trusted)
 	}
 	else
 	{
-		elog(ERROR, 
+		elog(ERROR,
 			 "cannot allocate second Perl interpreter on this platform");
-
 	}
-	
 }
 
 
@@ -425,7 +423,7 @@ plperl_init_interp(void)
 		elog(ERROR, "could not allocate Perl interpreter");
 
 	perl_construct(plperl_held_interp);
-	perl_parse(plperl_held_interp, plperl_init_shared_libs, 
+	perl_parse(plperl_held_interp, plperl_init_shared_libs,
 			   3, embedding, NULL);
 	perl_run(plperl_held_interp);
 
@@ -434,7 +432,7 @@ plperl_init_interp(void)
 		SV *res;
 
 		res = eval_pv(TEST_FOR_MULTI,TRUE);
-		can_run_two = SvIV(res); 
+		can_run_two = SvIV(res);
 		interp_state = INTERP_HELD;
 	}
 
@@ -1430,7 +1428,7 @@ compile_plperl_function(Oid fn_oid, bool is_trigger)
 	/************************************************************
 	 * Lookup the internal proc name in the hashtable
 	 ************************************************************/
-	hash_entry = hash_search(plperl_proc_hash, internal_proname, 
+	hash_entry = hash_search(plperl_proc_hash, internal_proname,
 							 HASH_FIND, NULL);
 
 	if (hash_entry)
@@ -1445,7 +1443,7 @@ compile_plperl_function(Oid fn_oid, bool is_trigger)
 		 * function's pg_proc entry without changing its OID.
 		 ************************************************************/
 		uptodate = (prodesc->fn_xmin == HeapTupleHeaderGetXmin(procTup->t_data) &&
-				prodesc->fn_cmin == HeapTupleHeaderGetCmin(procTup->t_data));
+				ItemPointerEquals(&prodesc->fn_tid, &procTup->t_self));
 
 		if (!uptodate)
 		{
@@ -1485,7 +1483,7 @@ compile_plperl_function(Oid fn_oid, bool is_trigger)
 		MemSet(prodesc, 0, sizeof(plperl_proc_desc));
 		prodesc->proname = strdup(internal_proname);
 		prodesc->fn_xmin = HeapTupleHeaderGetXmin(procTup->t_data);
-		prodesc->fn_cmin = HeapTupleHeaderGetCmin(procTup->t_data);
+		prodesc->fn_tid = procTup->t_self;
 
 		/* Remember if function is STABLE/IMMUTABLE */
 		prodesc->fn_readonly =
@@ -2128,9 +2126,9 @@ plperl_spi_prepare(char *query, int argc, SV **argv)
 	PG_TRY();
 	{
 		/************************************************************
-		 * Resolve argument type names and then look them up by oid 
-         * in the system cache, and remember the required information 
-         * for input conversion.
+		 * Resolve argument type names and then look them up by oid
+		 * in the system cache, and remember the required information
+		 * for input conversion.
 		 ************************************************************/
 		for (i = 0; i < argc; i++)
 		{
@@ -2523,8 +2521,8 @@ plperl_spi_freeplan(char *query)
 	 * free all memory before SPI_freeplan, so if it dies, nothing will be
 	 * left over
 	 */
-	hash_search(plperl_query_hash, query, 
-				HASH_REMOVE,NULL);
+	hash_search(plperl_query_hash, query,
+				HASH_REMOVE, NULL);
 
 	plan = qdesc->plan;
 	free(qdesc->argtypes);
diff --git a/src/pl/plpgsql/src/pl_comp.c b/src/pl/plpgsql/src/pl_comp.c
index c342ed3e85..44fae0f1b2 100644
--- a/src/pl/plpgsql/src/pl_comp.c
+++ b/src/pl/plpgsql/src/pl_comp.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.112 2007/02/08 18:37:14 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.113 2007/02/09 03:35:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -165,7 +165,7 @@ recheck:
 	{
 		/* We have a compiled function, but is it still valid? */
 		if (function->fn_xmin == HeapTupleHeaderGetXmin(procTup->t_data) &&
-			function->fn_cmin == HeapTupleHeaderGetCmin(procTup->t_data))
+			ItemPointerEquals(&function->fn_tid, &procTup->t_self))
 			function_valid = true;
 		else
 		{
@@ -355,7 +355,7 @@ do_compile(FunctionCallInfo fcinfo,
 	function->fn_name = pstrdup(NameStr(procStruct->proname));
 	function->fn_oid = fcinfo->flinfo->fn_oid;
 	function->fn_xmin = HeapTupleHeaderGetXmin(procTup->t_data);
-	function->fn_cmin = HeapTupleHeaderGetCmin(procTup->t_data);
+	function->fn_tid = procTup->t_self;
 	function->fn_functype = functype;
 	function->fn_cxt = func_cxt;
 	function->out_param_varno = -1;		/* set up for no OUT param */
diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index dad5ba5bb4..9f29fcd5da 100644
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.84 2007/01/30 22:05:13 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.85 2007/02/09 03:35:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -547,7 +547,7 @@ typedef struct PLpgSQL_function
 	char	   *fn_name;
 	Oid			fn_oid;
 	TransactionId fn_xmin;
-	CommandId	fn_cmin;
+	ItemPointerData fn_tid;
 	int			fn_functype;
 	PLpgSQL_func_hashkey *fn_hashkey;	/* back-link to hashtable key */
 	MemoryContext fn_cxt;
diff --git a/src/pl/plpython/plpython.c b/src/pl/plpython/plpython.c
index cd0f701581..90a3f87b15 100644
--- a/src/pl/plpython/plpython.c
+++ b/src/pl/plpython/plpython.c
@@ -1,7 +1,7 @@
 /**********************************************************************
  * plpython.c - python as a procedural language for PostgreSQL
  *
- *	$PostgreSQL: pgsql/src/pl/plpython/plpython.c,v 1.94 2007/02/01 19:10:30 momjian Exp $
+ *	$PostgreSQL: pgsql/src/pl/plpython/plpython.c,v 1.95 2007/02/09 03:35:35 tgl Exp $
  *
  *********************************************************************
  */
@@ -123,7 +123,7 @@ typedef struct PLyProcedure
 	char	   *proname;		/* SQL name of procedure */
 	char	   *pyname;			/* Python name of procedure */
 	TransactionId fn_xmin;
-	CommandId	fn_cmin;
+	ItemPointerData fn_tid;
 	bool		fn_readonly;
 	PLyTypeInfo result;			/* also used to store info for trigger tuple
 								 * type */
@@ -1100,7 +1100,7 @@ PLy_procedure_get(FunctionCallInfo fcinfo, Oid tgreloid)
 			elog(FATAL, "proc->me != plproc");
 		/* did we find an up-to-date cache entry? */
 		if (proc->fn_xmin != HeapTupleHeaderGetXmin(procTup->t_data) ||
-			proc->fn_cmin != HeapTupleHeaderGetCmin(procTup->t_data))
+			!ItemPointerEquals(&proc->fn_tid, &procTup->t_self))
 		{
 			Py_DECREF(plproc);
 			proc = NULL;
@@ -1151,7 +1151,7 @@ PLy_procedure_create(FunctionCallInfo fcinfo, Oid tgreloid,
 	proc->proname = PLy_strdup(NameStr(procStruct->proname));
 	proc->pyname = PLy_strdup(procName);
 	proc->fn_xmin = HeapTupleHeaderGetXmin(procTup->t_data);
-	proc->fn_cmin = HeapTupleHeaderGetCmin(procTup->t_data);
+	proc->fn_tid = procTup->t_self;
 	/* Remember if function is STABLE/IMMUTABLE */
 	proc->fn_readonly =
 		(procStruct->provolatile != PROVOLATILE_VOLATILE);
diff --git a/src/pl/tcl/pltcl.c b/src/pl/tcl/pltcl.c
index 7611fa7cc7..0477fa8c56 100644
--- a/src/pl/tcl/pltcl.c
+++ b/src/pl/tcl/pltcl.c
@@ -2,7 +2,7 @@
  * pltcl.c		- PostgreSQL support for Tcl as
  *				  procedural language (PL)
  *
- *	  $PostgreSQL: pgsql/src/pl/tcl/pltcl.c,v 1.109 2007/02/01 19:10:30 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/pl/tcl/pltcl.c,v 1.110 2007/02/09 03:35:35 tgl Exp $
  *
  **********************************************************************/
 
@@ -76,7 +76,7 @@ typedef struct pltcl_proc_desc
 {
 	char	   *proname;
 	TransactionId fn_xmin;
-	CommandId	fn_cmin;
+	ItemPointerData fn_tid;
 	bool		fn_readonly;
 	bool		lanpltrusted;
 	FmgrInfo	result_in_func;
@@ -962,7 +962,7 @@ compile_pltcl_function(Oid fn_oid, Oid tgreloid)
 		prodesc = (pltcl_proc_desc *) Tcl_GetHashValue(hashent);
 
 		uptodate = (prodesc->fn_xmin == HeapTupleHeaderGetXmin(procTup->t_data) &&
-				prodesc->fn_cmin == HeapTupleHeaderGetCmin(procTup->t_data));
+				ItemPointerEquals(&prodesc->fn_tid, &procTup->t_self));
 
 		if (!uptodate)
 		{
@@ -1004,7 +1004,7 @@ compile_pltcl_function(Oid fn_oid, Oid tgreloid)
 		MemSet(prodesc, 0, sizeof(pltcl_proc_desc));
 		prodesc->proname = strdup(internal_proname);
 		prodesc->fn_xmin = HeapTupleHeaderGetXmin(procTup->t_data);
-		prodesc->fn_cmin = HeapTupleHeaderGetCmin(procTup->t_data);
+		prodesc->fn_tid = procTup->t_self;
 
 		/* Remember if function is STABLE/IMMUTABLE */
 		prodesc->fn_readonly =
diff --git a/src/test/regress/expected/combocid.out b/src/test/regress/expected/combocid.out
new file mode 100644
index 0000000000..14e45fe489
--- /dev/null
+++ b/src/test/regress/expected/combocid.out
@@ -0,0 +1,242 @@
+--
+-- Tests for some likely failure cases with combo cmin/cmax mechanism
+--
+CREATE TEMP TABLE combocidtest (foobar int);
+BEGIN;
+-- a few dummy ops to push up the CommandId counter
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+INSERT INTO combocidtest VALUES (1);
+INSERT INTO combocidtest VALUES (2);
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |   10 |      1
+ (0,2) |   11 |      2
+(2 rows)
+
+SAVEPOINT s1;
+UPDATE combocidtest SET foobar = foobar + 10;
+-- here we should see only updated tuples
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,3) |   13 |     11
+ (0,4) |   13 |     12
+(2 rows)
+
+ROLLBACK TO s1;
+-- now we should see old tuples, but with combo CIDs starting at 0
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    0 |      1
+ (0,2) |    1 |      2
+(2 rows)
+
+COMMIT;
+-- combo data is not there anymore, but should still see tuples
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    0 |      1
+ (0,2) |    1 |      2
+(2 rows)
+
+-- Test combo cids with portals
+BEGIN;
+INSERT INTO combocidtest VALUES (333);
+DECLARE c CURSOR FOR SELECT ctid,cmin,* FROM combocidtest;
+DELETE FROM combocidtest;
+FETCH ALL FROM c;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    2 |      1
+ (0,2) |    2 |      2
+ (0,5) |    0 |    333
+(3 rows)
+
+ROLLBACK;
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    2 |      1
+ (0,2) |    2 |      2
+(2 rows)
+
+-- check behavior with locked tuples
+BEGIN;
+-- a few dummy ops to push up the CommandId counter
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+INSERT INTO combocidtest VALUES (444);
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    2 |      1
+ (0,2) |    2 |      2
+ (0,6) |   10 |    444
+(3 rows)
+
+SAVEPOINT s1;
+-- this doesn't affect cmin
+SELECT ctid,cmin,* FROM combocidtest FOR UPDATE;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    2 |      1
+ (0,2) |    2 |      2
+ (0,6) |   10 |    444
+(3 rows)
+
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |    2 |      1
+ (0,2) |    2 |      2
+ (0,6) |   10 |    444
+(3 rows)
+
+-- but this does
+UPDATE combocidtest SET foobar = foobar + 10;
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,7) |   14 |     11
+ (0,8) |   14 |     12
+ (0,9) |   14 |    454
+(3 rows)
+
+ROLLBACK TO s1;
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |   14 |      1
+ (0,2) |   14 |      2
+ (0,6) |    0 |    444
+(3 rows)
+
+COMMIT;
+SELECT ctid,cmin,* FROM combocidtest;
+ ctid  | cmin | foobar 
+-------+------+--------
+ (0,1) |   14 |      1
+ (0,2) |   14 |      2
+ (0,6) |    0 |    444
+(3 rows)
+
diff --git a/src/test/regress/expected/without_oid.out b/src/test/regress/expected/without_oid.out
index c32daf815d..cb2c0c0137 100644
--- a/src/test/regress/expected/without_oid.out
+++ b/src/test/regress/expected/without_oid.out
@@ -5,14 +5,15 @@
 -- This test tries to verify that WITHOUT OIDS actually saves space.
 -- On machines where MAXALIGN is 8, WITHOUT OIDS may or may not save any
 -- space, depending on the size of the tuple header + null bitmap.
--- As of 8.0 we need a 9-bit null bitmap to force the difference to appear.
+-- As of 8.3 we need a null bitmap of 8 or less bits for the difference
+-- to appear.
 --
 CREATE TABLE wi (i INT,
                  n1 int, n2 int, n3 int, n4 int,
-                 n5 int, n6 int, n7 int, n8 int) WITH OIDS;
+                 n5 int, n6 int, n7 int) WITH OIDS;
 CREATE TABLE wo (i INT,
                  n1 int, n2 int, n3 int, n4 int,
-                 n5 int, n6 int, n7 int, n8 int) WITHOUT OIDS;
+                 n5 int, n6 int, n7 int) WITHOUT OIDS;
 INSERT INTO wi VALUES (1);  -- 1
 INSERT INTO wo SELECT i FROM wi;  -- 1
 INSERT INTO wo SELECT i+1 FROM wi;  -- 1+1=2
diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule
index efc1f1fef6..096d2c1c7a 100644
--- a/src/test/regress/parallel_schedule
+++ b/src/test/regress/parallel_schedule
@@ -1,6 +1,6 @@
 # ----------
 # The first group of parallel test
-# $PostgreSQL: pgsql/src/test/regress/parallel_schedule,v 1.38 2007/01/28 16:16:54 neilc Exp $
+# $PostgreSQL: pgsql/src/test/regress/parallel_schedule,v 1.39 2007/02/09 03:35:35 tgl Exp $
 # ----------
 test: boolean char name varchar text int2 int4 int8 oid float4 float8 bit numeric uuid
 
@@ -69,7 +69,7 @@ test: misc
 # ----------
 # The fifth group of parallel test
 # ----------
-test: select_views portals_p2 rules foreign_key cluster dependency guc
+test: select_views portals_p2 rules foreign_key cluster dependency guc combocid
 
 # ----------
 # The sixth group of parallel test
diff --git a/src/test/regress/serial_schedule b/src/test/regress/serial_schedule
index 75e8b83138..d109dabdc2 100644
--- a/src/test/regress/serial_schedule
+++ b/src/test/regress/serial_schedule
@@ -1,4 +1,4 @@
-# $PostgreSQL: pgsql/src/test/regress/serial_schedule,v 1.36 2007/01/28 16:16:54 neilc Exp $
+# $PostgreSQL: pgsql/src/test/regress/serial_schedule,v 1.37 2007/02/09 03:35:35 tgl Exp $
 # This should probably be in an order similar to parallel_schedule.
 test: boolean
 test: char
@@ -88,6 +88,7 @@ test: foreign_key
 test: cluster
 test: dependency
 test: guc
+test: combocid
 test: limit
 test: plpgsql
 test: copy2
diff --git a/src/test/regress/sql/combocid.sql b/src/test/regress/sql/combocid.sql
new file mode 100644
index 0000000000..3f30839b1f
--- /dev/null
+++ b/src/test/regress/sql/combocid.sql
@@ -0,0 +1,93 @@
+--
+-- Tests for some likely failure cases with combo cmin/cmax mechanism
+--
+CREATE TEMP TABLE combocidtest (foobar int);
+
+BEGIN;
+
+-- a few dummy ops to push up the CommandId counter
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+
+INSERT INTO combocidtest VALUES (1);
+INSERT INTO combocidtest VALUES (2);
+
+SELECT ctid,cmin,* FROM combocidtest;
+
+SAVEPOINT s1;
+
+UPDATE combocidtest SET foobar = foobar + 10;
+
+-- here we should see only updated tuples
+SELECT ctid,cmin,* FROM combocidtest;
+
+ROLLBACK TO s1;
+
+-- now we should see old tuples, but with combo CIDs starting at 0
+SELECT ctid,cmin,* FROM combocidtest;
+
+COMMIT;
+
+-- combo data is not there anymore, but should still see tuples
+SELECT ctid,cmin,* FROM combocidtest;
+
+-- Test combo cids with portals
+BEGIN;
+
+INSERT INTO combocidtest VALUES (333);
+
+DECLARE c CURSOR FOR SELECT ctid,cmin,* FROM combocidtest;
+
+DELETE FROM combocidtest;
+
+FETCH ALL FROM c;
+
+ROLLBACK;
+
+SELECT ctid,cmin,* FROM combocidtest;
+
+-- check behavior with locked tuples
+BEGIN;
+
+-- a few dummy ops to push up the CommandId counter
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+SELECT 1;
+
+INSERT INTO combocidtest VALUES (444);
+
+SELECT ctid,cmin,* FROM combocidtest;
+
+SAVEPOINT s1;
+
+-- this doesn't affect cmin
+SELECT ctid,cmin,* FROM combocidtest FOR UPDATE;
+SELECT ctid,cmin,* FROM combocidtest;
+
+-- but this does
+UPDATE combocidtest SET foobar = foobar + 10;
+
+SELECT ctid,cmin,* FROM combocidtest;
+
+ROLLBACK TO s1;
+
+SELECT ctid,cmin,* FROM combocidtest;
+
+COMMIT;
+
+SELECT ctid,cmin,* FROM combocidtest;
diff --git a/src/test/regress/sql/without_oid.sql b/src/test/regress/sql/without_oid.sql
index 1a10a8533d..9fbb454d4d 100644
--- a/src/test/regress/sql/without_oid.sql
+++ b/src/test/regress/sql/without_oid.sql
@@ -6,14 +6,15 @@
 -- This test tries to verify that WITHOUT OIDS actually saves space.
 -- On machines where MAXALIGN is 8, WITHOUT OIDS may or may not save any
 -- space, depending on the size of the tuple header + null bitmap.
--- As of 8.0 we need a 9-bit null bitmap to force the difference to appear.
+-- As of 8.3 we need a null bitmap of 8 or less bits for the difference
+-- to appear.
 --
 CREATE TABLE wi (i INT,
                  n1 int, n2 int, n3 int, n4 int,
-                 n5 int, n6 int, n7 int, n8 int) WITH OIDS;
+                 n5 int, n6 int, n7 int) WITH OIDS;
 CREATE TABLE wo (i INT,
                  n1 int, n2 int, n3 int, n4 int,
-                 n5 int, n6 int, n7 int, n8 int) WITHOUT OIDS;
+                 n5 int, n6 int, n7 int) WITHOUT OIDS;
 
 INSERT INTO wi VALUES (1);  -- 1
 INSERT INTO wo SELECT i FROM wi;  -- 1