From: Giulio Cesare Solaroli <giulio.cesare@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Finalizing commit taking very long
Date: Wed, 24 Oct 2007 12:44:35 +0200
Message-ID: <ff737ac30710240344v4391d2eeq957e91dca6c2f9e0@mail.gmail.com> (raw)
Hello,
I am having a strange latency problem on my instance of Postgres that
I don't know how to investigate.
I am accessing the db instance using a Java application and the
Cayenne mapping framework. Everything works fine, except when it is
time to delete a user account (that is a user of the application, not
of Postgres).
Deleting an account trigger a (sort-of) cascade delete to remove also
all the dependent records stored on the db. The cascade constraints
are managed by the Cayenne library, and the db receives a list of
delete statements for all the rows of the different tables that should
be deleted; this is probably not optimal from a db point of view, but
is extremely convenient from an application point of view.
Anyway, the deletion of all the records is executed without much
problems (I had a huge slowdown here a few weeks ago, but I was
missing an index on a constraint).
Obviously, all the delete statements are grouped into a single
transaction; and when it is time to commit this transaction, the db
instance takes "forever".
Here are some logs taken from the db server:
[ lot of delete statements skipped]
2007-10-24 12:13:17 CEST LOG: statement: EXECUTE <unnamed> [PREPARE:
DELETE FROM connection.USRCNN WHERE ID_USRCNN = $1]
2007-10-24 12:13:17 CEST LOG: duration: 0.206 ms
2007-10-24 12:13:17 CEST LOG: duration: 0.206 ms statement: EXECUTE
<unnamed> [PREPARE: DELETE FROM connection.USRCNN WHERE ID_USRCNN =
$1]
2007-10-24 12:13:17 CEST LOG: statement: PREPARE <unnamed> AS DELETE
FROM clipperz.USR WHERE ID_USR = $1
2007-10-24 12:13:17 CEST LOG: statement: <BIND>
2007-10-24 12:13:17 CEST LOG: statement: EXECUTE <unnamed> [PREPARE:
DELETE FROM clipperz.USR WHERE ID_USR = $1]
2007-10-24 12:13:17 CEST LOG: duration: 0.761 ms
2007-10-24 12:13:17 CEST LOG: duration: 0.761 ms statement: EXECUTE
<unnamed> [PREPARE: DELETE FROM clipperz.USR WHERE ID_USR = $1]
2007-10-24 12:13:17 CEST LOG: statement: <BIND>
2007-10-24 12:13:17 CEST LOG: statement: EXECUTE <unnamed> [PREPARE: COMMIT]
2007-10-24 12:13:51 CEST LOG: autovacuum: processing database "clipperz_beta"
2007-10-24 12:14:51 CEST LOG: autovacuum: processing database "clipperz_beta"
2007-10-24 12:15:10 CEST LOG: duration: 113300.147 ms
2007-10-24 12:15:10 CEST LOG: duration: 113300.147 ms statement:
EXECUTE <unnamed> [PREPARE: COMMIT]
As you may notice, the commit phase takes almost 2 full minutes. :-(
How can I understand what is going on on that timeframe in order to
try to fix it?
Thanks for your attention.
Best regards,
Giulio Cesare
PS: I run my development machine on a MacOS, with Postgres running on
a Parallels virtual machine. I don't think this really matters for the
above problem, but in case ...
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To: pgsql-performance@postgresql.org
Cc: giulio.cesare@gmail.com
Subject: Re: Finalizing commit taking very long
In-Reply-To: <ff737ac30710240344v4391d2eeq957e91dca6c2f9e0@mail.gmail.com>
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