Re: User concurrency thresholding: where do I look? - Mailing list pgsql-performance

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