Optimise btree delete processing when no active backends.

Clarify comments, downgrade a message to DEBUG and remove some
debug counters. Direct from ideas by Heikki Linnakangas.

diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index 0d342eeb85f6f300e05bfe2b636992da82b13091..7b5b27315e5556fa9bf9473216975b11ab09d8d3 100644 (file)
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.66 2010/04/19 17:54:48 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.67 2010/04/22 08:04:24 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -578,9 +578,17 @@ btree_xlog_delete_get_latestRemovedXid(XLogRecord *record)
        OffsetNumber    hoffnum;
        TransactionId   latestRemovedXid = InvalidTransactionId;
        TransactionId   htupxid = InvalidTransactionId;
-       int num_unused = 0, num_redirect = 0, num_dead = 0;
        int i;
 
+       /*
+        * If there's nothing running on the standby we don't need to derive
+        * a full latestRemovedXid value, so use a fast path out of here.
+        * That returns InvalidTransactionId, and so will conflict with
+        * users, but since we just worked out that's zero people, its OK.
+        */
+       if (CountDBBackends(InvalidOid) == 0)
+               return latestRemovedXid;
+
        /*
         * Get index page
         */
@@ -629,7 +637,6 @@ btree_xlog_delete_get_latestRemovedXid(XLogRecord *record)
                 */
                while (ItemIdIsRedirected(hitemid))
                {
-                       num_redirect++;
                        hoffnum = ItemIdGetRedirect(hitemid);
                        hitemid = PageGetItemId(hpage, hoffnum);
                        CHECK_FOR_INTERRUPTS();
@@ -662,25 +669,23 @@ btree_xlog_delete_get_latestRemovedXid(XLogRecord *record)
                         * marked on LP_NORMAL items. So we just ignore this item and move
                         * onto the next, for the purposes of calculating latestRemovedxids.
                         */
-                       num_dead++;
                }
                else
-               {
                        Assert(!ItemIdIsUsed(hitemid));
-                       num_unused++;
-               }
 
                UnlockReleaseBuffer(hbuffer);
        }
 
        UnlockReleaseBuffer(ibuffer);
 
-       Assert(num_unused == 0);
-
        /*
         * Note that if all heap tuples were LP_DEAD then we will be
-        * returning InvalidTransactionId here. This seems very unlikely
-        * in practice.
+        * returning InvalidTransactionId here. That can happen if we are
+        * re-replaying this record type, though that will be before the
+        * consistency point and will not cause problems. It should
+        * happen very rarely after the consistency point, though note
+        * that we can't tell the difference between this and the fast
+        * path exit above. May need to change that in future.
         */
        return latestRemovedXid;
 }
@@ -963,13 +968,6 @@ btree_redo(XLogRecPtr lsn, XLogRecord *record)
                                        TransactionId latestRemovedXid = btree_xlog_delete_get_latestRemovedXid(record);
                                        xl_btree_delete *xlrec = (xl_btree_delete *) XLogRecGetData(record);
 
-                                       /*
-                                        * XXX Currently we put everybody on death row, because
-                                        * currently _bt_delitems() supplies InvalidTransactionId.
-                                        * This can be fairly painful, so providing a better value
-                                        * here is worth some thought and possibly some effort to
-                                        * improve.
-                                        */
                                        ResolveRecoveryConflictWithSnapshot(latestRemovedXid, xlrec->node);
                                }
                                break;

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 9aef06fca789db85f9113644962d1326522b3a15..2dde056a9792f9ec951ebfbabac60dc7dffdff16 100644 (file)
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.65 2010/04/21 19:08:14 sriggs Exp $
+ *       $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.66 2010/04/22 08:04:25 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1839,7 +1839,8 @@ CountDBBackends(Oid databaseid)
 
                if (proc->pid == 0)
                        continue;                       /* do not count prepared xacts */
-               if (proc->databaseId == databaseid)
+               if (!OidIsValid(databaseid) ||
+                       proc->databaseId == databaseid)
                        count++;
        }
 

diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 4d3cecb455b5e32f5b658cd5817e5a5af8e61ac0..029d807079143b537eb75ec8bac6cb4bd428c854 100644 (file)
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/storage/ipc/standby.c,v 1.17 2010/04/21 19:08:14 sriggs Exp $
+ *       $PostgreSQL: pgsql/src/backend/storage/ipc/standby.c,v 1.18 2010/04/22 08:04:25 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -248,7 +248,7 @@ ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid, RelFileNode
 
        /*
         * If we get passed InvalidTransactionId then we are a little surprised,
-        * but it is theoretically possible, so spit out a LOG message, but not
+        * but it is theoretically possible, so spit out a DEBUG1 message, but not
         * one that needs translating.
         *
         * We grab latestCompletedXid instead because this is the very latest
@@ -256,7 +256,7 @@ ResolveRecoveryConflictWithSnapshot(TransactionId latestRemovedXid, RelFileNode
         */
        if (!TransactionIdIsValid(latestRemovedXid))
        {
-               elog(LOG, "Invalid latestRemovedXid reported, using latestCompletedXid instead");
+               elog(DEBUG1, "Invalid latestremovexXid reported, using latestcompletedxid instead");
 
                LWLockAcquire(ProcArrayLock, LW_SHARED);
                latestRemovedXid = ShmemVariableCache->latestCompletedXid;