From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 15 Jan 2008 21:20:28 +0000 (+0000)
Subject: Prevent CLUSTER from decreasing a relation's relfrozenxid.  Bug
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=de56b9ec34e9efe8b44ec7fc5e88a413187d2b24;p=users%2Fbernd%2Fpostgres.git

Prevent CLUSTER from decreasing a relation's relfrozenxid.  Bug
introduced in rewrite to make CLUSTER MVCC-safe.
---

diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 9c4ff8e5ca..ecefb216af 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -751,6 +751,13 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 	vacuum_set_xid_limits(-1, OldHeap->rd_rel->relisshared,
 						  &OldestXmin, &FreezeXid);
 
+	/*
+	 * FreezeXid will become the table's new relfrozenxid, and that mustn't
+	 * go backwards, so take the max.
+	 */
+	if (TransactionIdPrecedes(FreezeXid, OldHeap->rd_rel->relfrozenxid))
+		FreezeXid = OldHeap->rd_rel->relfrozenxid;
+
 	/* Initialize the rewrite operation */
 	rwstate = begin_heap_rewrite(NewHeap, OldestXmin, FreezeXid, use_wal);