Tom Lane <[email protected]> writes:

> a_ogawa <[email protected]> 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.

The effect of the patch that I measured is as follows:

o Execution time that executed the SQL ten times.
(1)Linux(CPU: Pentium III, Compiler option: -O2)
 - original: 24.960s
 - patched : 23.114s

(2)Linux(CPU: Pentium 4, Compiler option: -O2)
 - original: 8.730s
 - patched : 7.962s

(3)Solaris(CPU: Ultra SPARC III, Compiler option: -O2)
 - original: 37.0s
 - patched : 33.7s

Atsushi Ogawa (a_ogawa)

diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index afbb57af68c1f37048552432ecca9a665fe5a983..dfe93b187d1072d3aa445fbc8a423ec7776efb79 100644 (file)
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -399,6 +399,17 @@ 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));