From def30e84c41389225ee9e56cb7c722980bab9746 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 20 Oct 2010 12:48:51 -0400
Subject: [PATCH] Don't try to fetch database name when SetTransactionIdLimit()
is executed outside a transaction.
This repairs brain fade in my patch of 2009-08-30: the reason we had been
storing oldest-database name, not OID, in ShmemVariableCache was of course
to avoid having to do a catalog lookup at times when it might be unsafe.
This error explains why Aleksandr Dushein is having trouble getting out of
an XID wraparound state in bug #5718, though not how he got into that state
in the first place. I suspect pg_upgrade is at fault there.
---
src/backend/access/transam/varsup.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
index 391724ea0fe..6f423bcf3a3 100644
--- a/src/backend/access/transam/varsup.c
+++ b/src/backend/access/transam/varsup.c
@@ -16,6 +16,7 @@
#include "access/clog.h"
#include "access/subtrans.h"
#include "access/transam.h"
+#include "access/xact.h"
#include "commands/dbcommands.h"
#include "miscadmin.h"
#include "postmaster/autovacuum.h"
@@ -346,13 +347,22 @@ SetTransactionIdLimit(TransactionId oldest_datfrozenxid, Oid oldest_datoid)
/* Give an immediate warning if past the wrap warn point */
if (TransactionIdFollowsOrEquals(curXid, xidWarnLimit) && !InRecovery)
{
- char *oldest_datname = get_database_name(oldest_datoid);
+ char *oldest_datname;
/*
- * Note: it's possible that get_database_name fails and returns NULL,
- * for example because the database just got dropped. We'll still
- * warn, even though the warning might now be unnecessary.
+ * We can be called when not inside a transaction, for example
+ * during StartupXLOG(). In such a case we cannot do database
+ * access, so we must just report the oldest DB's OID.
+ *
+ * Note: it's also possible that get_database_name fails and returns
+ * NULL, for example because the database just got dropped. We'll
+ * still warn, even though the warning might now be unnecessary.
*/
+ if (IsTransactionState())
+ oldest_datname = get_database_name(oldest_datoid);
+ else
+ oldest_datname = NULL;
+
if (oldest_datname)
ereport(WARNING,
(errmsg("database \"%s\" must be vacuumed within %u transactions",
--
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