On Thu, 2007-07-26 at 11:27 -0400, Jignesh K. Shah wrote:
> However at 900 Users where the big drop in throughput occurs:
> It gives a different top "consumer" of time:
postgres`LWLockAcquire+0x1c8
> postgres`SimpleLruReadPage+0x1ac
> postgres`TransactionIdGetStatus+0x14
> postgres`TransactionLogFetch+0x58
TransactionIdGetStatus doesn't directly call SimpleLruReadPage().
Presumably the compiler has been rearranging things??
Looks like you're out of clog buffers. It seems like the clog buffers
aren't big enough to hold clog pages for long enough and the SELECT FOR
SHARE processing is leaving lots of additional read locks that are
increasing the number of clog requests for older xids.
Try the enclosed patch.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
Index: src/include/access/clog.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/access/clog.h,v
retrieving revision 1.19
diff -c -r1.19 clog.h
*** src/include/access/clog.h 5 Jan 2007 22:19:50 -0000 1.19
--- src/include/access/clog.h 26 Jul 2007 15:44:58 -0000
***************
*** 29,35 ****
/* Number of SLRU buffers to use for clog */
! #define NUM_CLOG_BUFFERS 8
extern void TransactionIdSetStatus(TransactionId xid, XidStatus status);
--- 29,35 ----
/* Number of SLRU buffers to use for clog */
! #define NUM_CLOG_BUFFERS 64
extern void TransactionIdSetStatus(TransactionId xid, XidStatus status);
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