Back out patch:

---------------------------------------------------------------------------

Tom Lane  writes:
> a_ogawa  writes:
> > It is a reasonable idea. However, the majority part of MemSet was not
> > able to be avoided by this idea. Because the per-tuple contexts are used
> > at the early stage of executor.
>
> Drat.  Well, what about changing that?  We could introduce additional
> contexts or change the startup behavior so that the ones that are
> frequently reset don't have any data in them unless you are working
> with pass-by-ref values inside the inner loop.

That might be possible. However, I think that we should change only
aset.c about this article.
I thought further: We can check whether context was used from the last
reset even when blocks list is not empty. Please see attached patch.

diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index f7550929f1f6c6de14af88bc3f908c5dc405f1cd..de56a2dc0101b6e7320e57152ca5874c66311b39 100644 (file)
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.61 2005/06/04 20:14:12 momjian Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/mmgr/aset.c,v 1.62 2005/06/04 22:57:22 momjian Exp $
  *
  * NOTE:
  * This is a new (Feb. 05, 1999) implementation of the allocation set
@@ -399,17 +399,6 @@ AllocSetReset(MemoryContext context)
    if (block == NULL)
        return;
 
-   /*
-    * When blocks list has only "keeper" block and freeptr of the block
-    * is initial value, the context is not used from last reset.
-    */
-   if (block == set->keeper && block->next == NULL)
-   {
-       char       *datastart = ((char *) block) + ALLOC_BLOCKHDRSZ;
-       if (block->freeptr == datastart)
-           return;
-   }
-
    /* Clear chunk freelists */
    MemSetAligned(set->freelist, 0, sizeof(set->freelist));