Need to hold ControlFileLock while updating control file. Update

minRecoveryPoint in control file when replaying a parameter change record,
to ensure that we don't allow hot standby on WAL generated without
wal_level='hot_standby' after a standby restart.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 99e53b763218d4ff85cbf8a0078856a9dfedb319..a39d455a7f0589470ae653f5740756ee492c8110 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.408 2010/05/02 02:10:33 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.409 2010/05/03 11:17:52 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -7920,11 +7920,28 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
                /* Update our copy of the parameters in pg_control */
                memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_parameter_change));
 
+               LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
                ControlFile->MaxConnections = xlrec.MaxConnections;
                ControlFile->max_prepared_xacts = xlrec.max_prepared_xacts;
                ControlFile->max_locks_per_xact = xlrec.max_locks_per_xact;
                ControlFile->wal_level = xlrec.wal_level;
+               /*
+                * Update minRecoveryPoint to ensure that if recovery is aborted,
+                * we recover back up to this point before allowing hot standby
+                * again. This is particularly important if wal_level was set to
+                * 'archive' before, and is now 'hot_standby', to ensure you don't
+                * run queries against the WAL preceding the wal_level change.
+                * Same applies to decreasing max_* settings.
+                */
+               minRecoveryPoint = ControlFile->minRecoveryPoint;
+               if ((minRecoveryPoint.xlogid != 0 || minRecoveryPoint.xrecoff != 0)
+                       && XLByteLT(minRecoveryPoint, lsn))
+               {
+                       ControlFile->minRecoveryPoint = lsn;
+               }
+
                UpdateControlFile();
+               LWLockRelease(ControlFileLock);
 
                /* Check to see if any changes to max_connections give problems */
                CheckRequiredParameterValues();