I have implemented your ideas for checking BLCKSZ = 1024, and having
initdb adjust shared buffers checks based on BLCKSZ.
Patch attached and applied.
---
Peter Eisentraut wrote:
The smallest BLCKSZ that you can compile is 256. But ...
The smallest BLCKSZ that actually works is 1024, because of this code in
guc.c:
case GUC_UNIT_BLOCKS:
val /= (BLCKSZ / 1024);
Maybe it's worth adding an #error here to prevent smaller sizes being
used?
The smallest BLCKSZ that passes the regression tests is 4096. With
smaller settings your get half a dozen ordering differences, which
seems OK.
The shared memory configuration code in initdb doesn't know about
BLCKSZ, so with smaller sizes you get less shared buffers. Maybe that
is worth fixing sometime.
Aside from that my pgbench testing clearly shows that block sizes larger
than 2048 become progressively slower. Go figure.
--
Peter Eisentraut
http://developer.postgresql.org/~petere/
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--
Bruce Momjian [EMAIL PROTECTED] http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
Index: src/bin/initdb/initdb.c
===
RCS file: /cvsroot/pgsql/src/bin/initdb/initdb.c,v
retrieving revision 1.133
diff -c -c -r1.133 initdb.c
*** src/bin/initdb/initdb.c 16 Feb 2007 02:10:07 - 1.133
--- src/bin/initdb/initdb.c 20 Feb 2007 23:46:19 -
***
*** 1208,1214
for (i = 0; i bufslen; i++)
{
! test_buffs = trial_bufs[i];
if (test_buffs = ok_buffers)
{
test_buffs = ok_buffers;
--- 1208,1215
for (i = 0; i bufslen; i++)
{
! /* Use same amount of memory, independent of BLCKSZ */
! test_buffs = (trial_bufs[i] * 8192) / BLCKSZ;
if (test_buffs = ok_buffers)
{
test_buffs = ok_buffers;
Index: src/include/pg_config_manual.h
===
RCS file: /cvsroot/pgsql/src/include/pg_config_manual.h,v
retrieving revision 1.24
diff -c -c -r1.24 pg_config_manual.h
*** src/include/pg_config_manual.h 6 Feb 2007 09:16:08 - 1.24
--- src/include/pg_config_manual.h 20 Feb 2007 23:46:19 -
***
*** 25,30
--- 25,34
*/
#define BLCKSZ 8192
+ #if BLCKSZ 1024
+ #error BLCKSZ must be = 1024
+ #endif
+
/*
* RELSEG_SIZE is the maximum number of blocks allowed in one disk
* file. Thus, the maximum size of a single file is RELSEG_SIZE *
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TIP 6: explain analyze is your friend
