Force VACUUM to recalculate oldestXmin even when we haven't changed our

own database's datfrozenxid, if the current value is old enough to be
forcing autovacuums or warning messages.  This ensures that a bogus
value is replaced as soon as possible.  Per a comment from Heikki.

diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
index f4dc2df0481f0a818416dff339735186561f4190..f8e3f365a151ff95307b14d136370ff66bc531c8 100644 (file)
--- a/src/backend/access/transam/varsup.c
+++ b/src/backend/access/transam/varsup.c
@@ -372,32 +372,41 @@ SetTransactionIdLimit(TransactionId oldest_datfrozenxid, Oid oldest_datoid)
 
 
 /*
- * TransactionIdLimitIsValid -- is the shared XID wrap-limit data sane?
+ * ForceTransactionIdLimitUpdate -- does the XID wrap-limit data need updating?
  *
  * We primarily check whether oldestXidDB is valid.  The cases we have in
  * mind are that that database was dropped, or the field was reset to zero
  * by pg_resetxlog.  In either case we should force recalculation of the
- * wrap limit.  In future we might add some more sanity checks here.
+ * wrap limit.  Also do it if oldestXid is old enough to be forcing
+ * autovacuums or other actions; this ensures we update our state as soon
+ * as possible once extra overhead is being incurred.
  */
 bool
-TransactionIdLimitIsValid(void)
+ForceTransactionIdLimitUpdate(void)
 {
+       TransactionId nextXid;
+       TransactionId xidVacLimit;
        TransactionId oldestXid;
        Oid                     oldestXidDB;
 
        /* Locking is probably not really necessary, but let's be careful */
        LWLockAcquire(XidGenLock, LW_SHARED);
+       nextXid = ShmemVariableCache->nextXid;
+       xidVacLimit = ShmemVariableCache->xidVacLimit;
        oldestXid = ShmemVariableCache->oldestXid;
        oldestXidDB = ShmemVariableCache->oldestXidDB;
        LWLockRelease(XidGenLock);
 
        if (!TransactionIdIsNormal(oldestXid))
-               return false;                   /* shouldn't happen, but just in case */
+               return true;                    /* shouldn't happen, but just in case */
+       if (TransactionIdFollowsOrEquals(nextXid, xidVacLimit) &&
+               TransactionIdIsValid(xidVacLimit))
+               return true;                    /* past VacLimit, don't delay updating */
        if (!SearchSysCacheExists(DATABASEOID,
                                                          ObjectIdGetDatum(oldestXidDB),
                                                          0, 0, 0))
-               return false;                   /* could happen, per comment above */
-       return true;
+               return true;                    /* could happen, per comments above */
+       return false;
 }
 
 

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 1349de2f728731ccb616899c6ac86f3eaf4a9613..c9c9baad54b664406ba710052e8e61e9acaacc10 100644 (file)
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -893,9 +893,10 @@ vac_update_datfrozenxid(void)
 
        /*
         * If we were able to advance datfrozenxid, see if we can truncate pg_clog.
-        * Also do it if the shared XID-wrap-limit info is stale.
+        * Also do it if the shared XID-wrap-limit info is stale, since this
+        * action will update that too.
         */
-       if (dirty || !TransactionIdLimitIsValid())
+       if (dirty || ForceTransactionIdLimitUpdate())
                vac_truncate_clog(newFrozenXid);
 }
 

diff --git a/src/include/access/transam.h b/src/include/access/transam.h
index 9b19a754e7fbddf69ca8d70b492c2610a10b6adb..8ce30e3ec4985d36462202542b930eb38b3dd524 100644 (file)
--- a/src/include/access/transam.h
+++ b/src/include/access/transam.h
@@ -156,7 +156,7 @@ extern TransactionId GetNewTransactionId(bool isSubXact);
 extern TransactionId ReadNewTransactionId(void);
 extern void SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
                                          Oid oldest_datoid);
-extern bool TransactionIdLimitIsValid(void);
+extern bool ForceTransactionIdLimitUpdate(void);
 extern Oid     GetNewObjectId(void);
 
 #endif   /* TRAMSAM_H */