[pgpool-general: 594] Re: load balancing seems to be bottlenecked by performance of master

Lazaro Ruben Garcia Martinez lgarciam at uci.cu
Tue Jun 5 22:28:54 JST 2012


What means "The size of the cache is vary from cache to cache, but typical size is 128" the size is in bytes? 

Regards. 

----- Mensaje original -----

> > On Mon, Jun 4, 2012 at 3:40 PM, Tatsuo Ishii <ishii at postgresql.org>
> > wrote:
> >>> You're correct, I only needed to perform a reload. I kept this
> >>> change
> >>> enabled for all of 36 seconds, and in that time there were 1597
> >>> times
> >>> that the following query was logged originating from the pgpool
> >>> server
> >>> IP address:
> >>> SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.oid ...
> >>>
> >>> 3204 times that the following query was logged originating from
> >>> the
> >>> pgpool server IP address:
> >>> SELECT count(*) FROM pg_class AS c, pg_namespace AS n WHERE
> >>> c.relname ...
> >>>
> >>> Those numbers seem excessive to me, but perhaps this is
> >>> expected/normal? It definitely seems like it would explain why
> >>> perf
> >>> always degrades whenever the master is very busy, if that volume
> >>> of
> >>> queries needs to be sustained.
> >>
> >> That depends on your use case. If client's query involves many
> >> tables,
> >> it requires many catalog lookups. Also the catalog cache of
> >> pgpool's
> >> life time is same as pgpool child process lifetime. If you would
> >> show
> >> me the complete log, I could make more precise analysis.
> >
> > Sure, attached as pg.log.gz.

> Analyzing the log I noticed several things:

> 1) I see many sessions which frequently connects/disconnects(over
> 1800
> in 36 seconds). That is, each session only lasts 20 ms in average.

> 2) A process issues exactly same query more than once. This suggests
> that relcache (catalog cache) size might be too small for your
> environment. The size of the cache is vary from cache to cache, but
> typical size is 128. So if you access more than 128 tables via
> pgpool, the cache replacement will happen. How many tables do you
> have?

> 2) The are many queries to check whether the table is a temporary one
> or not(1589 times). Even if we increase the relcache size, we
> cannot avoid this since the cache's life time is session. So it
> might be worth to invent new swich to skip the check.
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese: http://www.sraoss.co.jp
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