Fix incomplete backpatch of pg_multixact truncation changes to <= 9.2

The backpatch of a95335b544d9c8377e9dc7a399d8e9a155895f82 to 9.2, 9.1
and 9.0 was incomplete, missing changes to xlog.c, primarily the call
to TrimMultiXact(). Testing presumably didn't show a problem without
these changes because TrimMultiXact() performs defense-in-depth work,
which is not strictly necessary.

It also missed moving StartupMultiXact() which would have been
problematic if a restartpoing happened in exactly the wrong moment,
causing a transient error.

Andres Freund

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8243ea62d7834d79d07406ae3904eaf724dd6436..190d86b752990ab6b1f5d1af3992c6cb20e9989b 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6530,6 +6530,12 @@ StartupXLOG(void)
        XLogCtl->ckptXidEpoch = checkPoint.nextXidEpoch;
        XLogCtl->ckptXid = checkPoint.nextXid;
 
+       /*
+        * Startup MultiXact.  We need to do this early because we need its state
+        * initialized because we attempt truncation during restartpoints.
+        */
+       StartupMultiXact();
+
        /*
         * We must replay WAL entries using the same TimeLineID they were created
         * under, so temporarily adopt the TLI indicated by the checkpoint (see
@@ -6696,8 +6702,9 @@ StartupXLOG(void)
                        ProcArrayInitRecovery(ShmemVariableCache->nextXid);
 
                        /*
-                        * Startup commit log and subtrans only. Other SLRUs are not
-                        * maintained during recovery and need not be started yet.
+                        * Startup commit log and subtrans only. MultiXact has already
+                        * been started up and other SLRUs are not maintained during
+                        * recovery and need not be started yet.
                         */
                        StartupCLOG();
                        StartupSUBTRANS(oldestActiveXID);
@@ -7238,7 +7245,7 @@ StartupXLOG(void)
        /*
         * Perform end of recovery actions for any SLRUs that need it.
         */
-       StartupMultiXact();
+       TrimMultiXact();
        TrimCLOG();
 
        /* Reload shared-memory state for prepared transactions */

diff --git a/src/include/access/multixact.h b/src/include/access/multixact.h
index e20573d01fb834e32a8440c799c99d334a1b8ebc..7f46c3eeea4e8fa2db817cda50570650ce73979f 100644 (file)
--- a/src/include/access/multixact.h
+++ b/src/include/access/multixact.h
@@ -59,6 +59,7 @@ extern Size MultiXactShmemSize(void);
 extern void MultiXactShmemInit(void);
 extern void BootStrapMultiXact(void);
 extern void StartupMultiXact(void);
+extern void TrimMultiXact(void);
 extern void ShutdownMultiXact(void);
 extern void MultiXactGetCheckptMulti(bool is_shutdown,
                                                 MultiXactId *nextMulti,