[pgpool-general: 479] Re: load balancing seems to be bottlenecked by performance of master

[Tatsuo Ishii]

> Greetings,
> I'm running pgpool-II-3.1.2 purely for load balancing in front of a 4
> node postgresql-9.1.3 cluster (all running on Linux-x86_64).  I'm
> using streaming replication with 3 hot standby servers.  I have the
> weighting distributed such that the master weight is set to '1' and
> the three standby servers are set to '33' each.  My intent was that
> this would nearly eliminate all read queries going to the master,
> however what I'm observing is that the overall performance seems to be
> bottlenecked by the performance of the master, even when queries
> aren't ultimately getting sent to the master.
> 
> For example, there are times when the load on the master is much
> higher than on the standby servers, and the master's overall
> performance is noticeably degraded.  When this occurs, I've found that
> establishing a database connection through pgpool with a SQL query
> that should normally go to one of the standby servers has very poor
> performance.  It seems like pgpool is silently doing something with
> the master (which is under load and slower to respond), before passing
> the query itself off to a standby server.
> 
> Is this expected behavior?

Yes. Pgpool needs to send query to system catalogs on primary to
analyze user queries (for example, if the refereed table is a
temporary table or not).
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp