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DELETE queries slow down

From: "Galantucci Giovanni" <Giovanni(dot)Galantucci(at)italtel(dot)it>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: DELETE queries slow down
Date: 2007-09-17 07:48:09
Message-ID: AF4EB29748E178458A0067661112724B0FCF74@BESONE.corp.dom (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hi all,

I have a problem with DELETE performance with postgres 7.4.

I have a database with 2 great tables (about 150,000 rows) continuously
updated, with 1000 - 1200 INSERT per second and 2 or 3 huge DELETE per
minute, in which we delete almost all the rows inserted in the 2 tables
during the previous minute.

I have a single, indexed foreign key between the 2 tables.


In this scenario we have always a problem with the delete:

For 1 or 2 hours we update only one table, and everything goes ok, where
DELETE last at most 6 or 7 seconds.

Then for a minute we do INSERT on both table, and everything continue
going ok, with DELETE that last about 10 seconds.

From that moment on, DELETES become timeless, and last for 240 and more

Then I can't recover from this state because INSERT continue with the
same rate and DELETE become more and more slow.

I do a vacuum analyze every minute.


What can I do to avoid or at least limit that problem?


I will be graceful to everyone who could help me.





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