[pgpool-general: 2034] Re: pgpool replication mode

Tatsuo Ishii ishii at postgresql.org
Thu Aug 15 08:16:42 JST 2013

> I'm very interested in using the replication mode as provided by pgpool but have some questions that are worrying me.
> 1/ What sort of overhead does it add if used instead of streaming replication.

In theory, write performance drops up to 50% of normal
PostgreSQL. This is the price of synchronous replication (streming
replication is not "true" synchrnouse replication).  Also itt depends
on your type of load. Maybe the slide I showed in PGCon this year
might help. See:


of page 21-22.

> 2/How are things like nextval handled so that each backend is in synch? Especially when selects are load balanced.

SELECTs including nextval etc. are treated as if they are write
queries. i.e. they are load balanced.

> 3/Are there diminishing returns on adding more backends.

I tried myself up to 4 backends(see the slide above). Not sure about
more backends.
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

> We want to scale as we get more clients, any advice would be appreciated. What is the best way to scale a postgresql based web app.
> Thanks in anticipation.
> Garry
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