Avoid O(N^2) behavior with lots of deferred triggers by making

deferredTriggerInvokeEvents only scan events added since it last ran.
Stephan Szabo, some corrections by Tom Lane.

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index d6f0f03666ded2ab95f7f2a760aaf2c1bdacd96e..8a62986ec445906345aa448d4c6d3a83fbf2bad6 100644 (file)
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.147 2003/03/31 20:47:51 momjian Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.148 2003/04/20 17:03:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1626,12 +1626,18 @@ static List *deftrig_trigstates;
  * Because this can grow pretty large, we don't use separate List nodes,
  * but instead thread the list through the dte_next fields of the member
  * nodes.  Saves just a few bytes per entry, but that adds up.
+ * 
+ * deftrig_events_imm holds the tail pointer as of the last 
+ * deferredTriggerInvokeEvents call; we can use this to avoid rescanning
+ * entries unnecessarily.  It is NULL if deferredTriggerInvokeEvents
+ * hasn't run since the last state change.
  *
  * XXX Need to be able to shove this data out to a file if it grows too
  *    large...
  * ----------
  */
 static DeferredTriggerEvent deftrig_events;
+static DeferredTriggerEvent deftrig_events_imm;
 static DeferredTriggerEvent deftrig_event_tail;
 
 
@@ -1845,7 +1851,7 @@ static void
 deferredTriggerInvokeEvents(bool immediate_only)
 {
    DeferredTriggerEvent event,
-               prev_event = NULL;
+               prev_event;
    MemoryContext per_tuple_context;
    Relation    rel = NULL;
    TriggerDesc *trigdesc = NULL;
@@ -1857,13 +1863,12 @@ deferredTriggerInvokeEvents(bool immediate_only)
     * are going to discard the whole event queue on return anyway, so no
     * need to bother with "retail" pfree's.
     *
-    * In a scenario with many commands in a transaction and many
-    * deferred-to-end-of-transaction triggers, it could get annoying to
-    * rescan all the deferred triggers at each command end. To speed this
-    * up, we could remember the actual end of the queue at EndQuery and
-    * examine only events that are newer. On state changes we simply
-    * reset the saved position to the beginning of the queue and process
-    * all events once with the new states.
+    * If immediate_only is true, we need only scan from where the end of
+    * the queue was at the previous deferredTriggerInvokeEvents call;
+    * any non-deferred events before that point are already fired.
+    * (But if the deferral state changes, we must reset the saved position
+    * to the beginning of the queue, so as to process all events once with
+    * the new states.  See DeferredTriggerSetState.)
     */
 
    /* Make a per-tuple memory context for trigger function calls */
@@ -1874,7 +1879,22 @@ deferredTriggerInvokeEvents(bool immediate_only)
                              ALLOCSET_DEFAULT_INITSIZE,
                              ALLOCSET_DEFAULT_MAXSIZE);
 
-   event = deftrig_events;
+   /*
+    * If immediate_only is true, then the only events that could need firing
+    * are those since deftrig_events_imm.  (But if deftrig_events_imm is
+    * NULL, we must scan the entire list.)
+    */
+   if (immediate_only && deftrig_events_imm != NULL)
+   {
+       prev_event = deftrig_events_imm;
+       event = prev_event->dte_next;
+   }
+   else
+   {
+       prev_event = NULL;
+       event = deftrig_events;
+   }
+
    while (event != NULL)
    {
        bool        still_deferred_ones = false;
@@ -1993,6 +2013,9 @@ deferredTriggerInvokeEvents(bool immediate_only)
    /* Update list tail pointer in case we just deleted tail event */
    deftrig_event_tail = prev_event;
 
+   /* Set the immediate event pointer for next time */
+   deftrig_events_imm = prev_event;
+
    /* Release working resources */
    if (rel)
        heap_close(rel, NoLock);
@@ -2051,6 +2074,7 @@ DeferredTriggerBeginXact(void)
    deftrig_trigstates = NIL;
 
    deftrig_events = NULL;
+   deftrig_events_imm = NULL;
    deftrig_event_tail = NULL;
 }
 
@@ -2280,8 +2304,11 @@ DeferredTriggerSetState(ConstraintsSetStmt *stmt)
     * CONSTRAINTS command applies retroactively. This happens "for free"
     * since we have already made the necessary modifications to the
     * constraints, and deferredTriggerEndQuery() is called by
-    * finish_xact_command().
+    * finish_xact_command().  But we must reset deferredTriggerInvokeEvents'
+    * tail pointer to make it rescan the entire list, in case some deferred
+    * events are now immediately invokable.
     */
+   deftrig_events_imm = NULL;
 }