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Date: Tue, 23 Jan 2007 08:11:11 -0800 (PST)
From: Subramaniam Aiylam <aiylam_s@yahoo.com>
Subject: Postgres processes have a burst of CPU usage
To: pgsql-performance@postgresql.org
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Message-ID: <519784.22637.qm@web60714.mail.yahoo.com>

Hello all,

  I have a setup in which four client machines access
a Postgres database (8.1.1) (on a Linux box). So,
there are connections from each machine to the
database; hence, the Linux box has about 2 postgres
processes associated with each machine.

  I am using the JDBC driver
(postgresql-8.1-404.jdbc3.jar) to talk to the
database. I am also using the Spring framework(1.2.2)
and Hibernate (3.0.5) on top of JDBC. I use Apache's
DBCP database connection pool (1.2.1).

  Now, there is one particular update that I make from
one of the client machines - this involves a
reasonably large object graph (from the Java point of
view). It deletes a bunch of rows (around 20 rows in
all) in 4-5 tables and inserts another bunch into the
same tables.

  When I do this, I see a big spike in the CPU usage
of postgres processes that are associated with ALL the
client machines, not just the one I executed the
delete/insert operation on. The spike seems to happen
a second or two AFTER the original update completes
and last for a few seconds.

  Is it that this operation is forcibly clearing some
client cache on ALL the postgres processes? Why is
there such an interdependency? Can I set some
parameter to turn this off?

Regards and thanks,
S.Aiylam


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