Move the tuple freezing point in CLUSTER to a point further back in the past,

to avoid losing useful Xid information in not-so-old tuples.  This makes
CLUSTER behave the same as VACUUM as far a tuple-freezing behavior goes
(though CLUSTER does not yet advance the table's relfrozenxid).

While at it, move the actual freezing operation in rewriteheap.c to a more
appropriate place, and document it thoroughly.  This part of the patch from
Tom Lane.

3 files changed, 18 insertions, 11 deletions

diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 656d7d710f0..3eee46fbd0a 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.159 2007/04/08 01:26:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.160 2007/05/17 15:28:29 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -29,6 +29,7 @@
 #include "catalog/namespace.h"
 #include "catalog/toasting.h"
 #include "commands/cluster.h"
+#include "commands/vacuum.h"
 #include "miscadmin.h"
 #include "storage/procarray.h"
 #include "utils/acl.h"
@@ -657,6 +658,7 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 	HeapTuple	tuple;
 	bool		use_wal;
 	TransactionId OldestXmin;
+	TransactionId FreezeXid;
 	RewriteState rwstate;
 
 	/*
@@ -688,11 +690,16 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 	/* use_wal off requires rd_targblock be initially invalid */
 	Assert(NewHeap->rd_targblock == InvalidBlockNumber);
 
-	/* Get the cutoff xmin we'll use to weed out dead tuples */
-	OldestXmin = GetOldestXmin(OldHeap->rd_rel->relisshared, true);
+	/*
+	 * compute xids used to freeze and weed out dead tuples.  We use -1
+	 * freeze_min_age to avoid having CLUSTER freeze tuples earlier than
+	 * a plain VACUUM would.
+	 */
+	vacuum_set_xid_limits(-1, OldHeap->rd_rel->relisshared,
+						  &OldestXmin, &FreezeXid);
 
 	/* Initialize the rewrite operation */
-	rwstate = begin_heap_rewrite(NewHeap, OldestXmin, use_wal);
+	rwstate = begin_heap_rewrite(NewHeap, OldestXmin, FreezeXid, use_wal);
 
 	/*
 	 * Scan through the OldHeap in OldIndex order and copy each tuple into the
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index f275448756f..93885579cbb 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.350 2007/04/16 18:29:50 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.351 2007/05/17 15:28:29 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -566,7 +566,7 @@ get_rel_oids(List *relids, const RangeVar *vacrel, const char *stmttype)
  * vacuum_set_xid_limits() -- compute oldest-Xmin and freeze cutoff points
  */
 void
-vacuum_set_xid_limits(VacuumStmt *vacstmt, bool sharedRel,
+vacuum_set_xid_limits(int freeze_min_age, bool sharedRel,
 					  TransactionId *oldestXmin,
 					  TransactionId *freezeLimit)
 {
@@ -588,12 +588,12 @@ vacuum_set_xid_limits(VacuumStmt *vacstmt, bool sharedRel,
 	Assert(TransactionIdIsNormal(*oldestXmin));
 
 	/*
-	 * Determine the minimum freeze age to use: as specified in the vacstmt,
+	 * Determine the minimum freeze age to use: as specified by the caller,
 	 * or vacuum_freeze_min_age, but in any case not more than half
 	 * autovacuum_freeze_max_age, so that autovacuums to prevent XID
 	 * wraparound won't occur too frequently.
 	 */
-	freezemin = vacstmt->freeze_min_age;
+	freezemin = freeze_min_age;
 	if (freezemin < 0)
 		freezemin = vacuum_freeze_min_age;
 	freezemin = Min(freezemin, autovacuum_freeze_max_age / 2);
@@ -1154,7 +1154,7 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 				i;
 	VRelStats  *vacrelstats;
 
-	vacuum_set_xid_limits(vacstmt, onerel->rd_rel->relisshared,
+	vacuum_set_xid_limits(vacstmt->freeze_min_age, onerel->rd_rel->relisshared,
 						  &OldestXmin, &FreezeLimit);
 
 	/*
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index 2b6d8a07f76..2c9a80540c3 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -36,7 +36,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.88 2007/04/30 03:23:48 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.89 2007/05/17 15:28:29 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -158,7 +158,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 	else
 		elevel = DEBUG2;
 
-	vacuum_set_xid_limits(vacstmt, onerel->rd_rel->relisshared,
+	vacuum_set_xid_limits(vacstmt->freeze_min_age, onerel->rd_rel->relisshared,
 						  &OldestXmin, &FreezeLimit);
 
 	vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));