From: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-docs@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] "distributed checkpoint"
Date: Fri, 7 Dec 2007 22:25:46 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0712072138270.10014@westnet.com> (raw)
In-Reply-To: <1197051730.4255.603.camel@ebony.site>
References: <20071206220348.GM8451@alvh.no-ip.org>
<5958.1196991889@sss.pgh.pa.us>
<20071206191944.1d7926d2@commandprompt.com>
<20071207034328.GB18310@fetter.org>
<1197051730.4255.603.camel@ebony.site>
On Fri, 7 Dec 2007, Simon Riggs wrote:
> "Smoothed" makes a lot of sense for me. We used to have a checkpoint
> spike, now we don't.
To be accurate, there used to be a huge and unavoidable spike, now there's
a control that aims to make it smaller. The problem hasn't completely
gone away yet.
With that in mind, let me start over. Here's what's in the release notes
right now:
"Distributed checkpoints prevent I/O spikes during checkpoints"
It's good this came up, because that is factually wrong; while the average
case is much better some OS-dependant aspects of the spike (what happens
at fsync) are certainly still there. I think it's easier to rewrite this
whole thing so it's technically accurate rather than a simple fix of the
wording, something like this:
"Checkpoint writes can be spread over a longer time period to smooth the
I/O spike during each checkpoint"
It's got spread, it's got smooth, and if I could have worked "silky" in
there too I would have.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-docs@postgresql.org
Cc: gsmith@gregsmith.com, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] "distributed checkpoint"
In-Reply-To: <Pine.GSO.4.64.0712072138270.10014@westnet.com>
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