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;