Avoid O(N^2) behavior in deferredTriggerAddEvent() for large numbers of

tuples inserted/deleted/updated in a single transaction.  On my machine,
this reduced the time to delete 80000 tuples in a foreign-key-referencing
table from ~15min to ~8sec.

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index d01ba4ec919a3b990754a399d18a76b583092581..7a013c076bdcfa0c5ca405c25756ae609f263dbd 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 1.86 2001/01/27 05:16:58 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.87 2001/03/12 23:02:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1152,14 +1152,16 @@ static bool deftrig_all_isdeferred;
 static List *deftrig_trigstates;
 
 /* ----------
- * The list of events during the entire transaction.
+ * The list of events during the entire transaction.  deftrig_events
+ * is the head, deftrig_event_tail is the last entry.
  *
- * XXX This must finally be held in a file because of the huge
- *        number of events that could occur in the real world.
+ * XXX Need to be able to shove this data out to a file if it grows too
+ *        large...
  * ----------
  */
 static int     deftrig_n_events;
 static List *deftrig_events;
+static List *deftrig_event_tail;
 
 
 /* ----------
@@ -1235,7 +1237,22 @@ deferredTriggerCheckState(Oid tgoid, int32 itemstate)
 static void
 deferredTriggerAddEvent(DeferredTriggerEvent event)
 {
-       deftrig_events = lappend(deftrig_events, event);
+       /*
+        * Since the event list could grow quite long, we keep track of the
+        * list tail and append there, rather than just doing a stupid "lappend".
+        * This avoids O(N^2) behavior for large numbers of events.
+        */
+       if (deftrig_event_tail == NIL)
+       {
+               /* first list entry */
+               deftrig_events = makeList1(event);
+               deftrig_event_tail = deftrig_events;
+       }
+       else
+       {
+               lnext(deftrig_event_tail) = makeList1(event);
+               deftrig_event_tail = lnext(deftrig_event_tail);
+       }
        deftrig_n_events++;
 }
 
@@ -1397,7 +1414,6 @@ deferredTriggerInvokeEvents(bool immediate_only)
        List       *el;
        DeferredTriggerEvent event;
        int                     still_deferred_ones;
-       int                     eventno = -1;
        int                     i;
        MemoryContext per_tuple_context;
 
@@ -1421,8 +1437,6 @@ deferredTriggerInvokeEvents(bool immediate_only)
 
        foreach(el, deftrig_events)
        {
-               eventno++;
-
                MemoryContextReset(per_tuple_context);
 
                /* ----------
@@ -1548,6 +1562,7 @@ DeferredTriggerBeginXact(void)
 
        deftrig_n_events = 0;
        deftrig_events = NIL;
+       deftrig_event_tail = NIL;
 }