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Checkpoints - what happens actually?

From: KÖPFERL Robert <robert(dot)koepferl(at)sonorys(dot)at>
To: pgsql-admin(at)postgresql(dot)org
Subject: Checkpoints - what happens actually?
Date: 2005-06-27 13:21:30
Message-ID: ED4E30DD9C43D5118DFB00508BBBA76EB167A2@neptun.sonorys.at (view raw or flat)
Thread:
Lists: pgsql-admin
Hi,

i went across a checkpoint problematic (90% load, near real time app). I've
read in pg-documentation what exists about CHECKPOINT and the configuration
parameters. But there're still many open questions as:

What actually happens if a checkpoint occours?
OK, all dirty pages of data files get written to disk...but

Are read requests (simple selects) still possible and quickly answered?

What happens to wite-operations? Do they get queued or can they be written
to xlog while the fsync is running?
Is it maybe really the case but wave of pending statements arises from the
reduced i/o capacity which is left due to the fsync?

How about increasing the interval more and more? Will this produce more and
more dirty pages or is it just that a possible restart will take a longer
time since the xlog is longer?

Questions over questions. Can you please give me a clearing little insight.

pgsql-admin by date

Next:From: hellz warenDate: 2005-06-27 13:30:43
Subject: Re: real time replication of pgsql database
Previous:From: Bruce MomjianDate: 2005-06-27 09:45:43
Subject: Re: DRDB?

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