Re: checkpointer continuous flushing

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: checkpointer continuous flushing
Date: 2016-01-07 10:27:13
Message-ID: alpine.DEB.2.10.1601071126020.5278@sto
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<Ooops, wrong from address, resent, sorry for the noise>

Hello Andres,

>>> Although I disagree with some aspects of Andres patch, I'm not a
>>> committer and I'm tired of arguing. I'm just planing to do minor changes
>>> to Andres version to fix a potential issue if the file is closed which
>>> flushing is in progress, but that will not change the overall shape of
>>> it.
>
> Are you working on that aspect?

I read your patch and I know what I want to try to have a small and simple
fix. I must admit that I have not really understood in which condition the
checkpointer would decide to close a file, but that does not mean that the
potential issue should not be addressed.

Also, I gave some thoughts about what should be done for bgwriter random IOs.
The idea is to implement some per-file sorting there and then do some LRU/LFU
combing. It would not interact much with the checkpointer, so for me the two
issues should be kept separate and this should not preclude changing the
checkpointer, esp. given the significant performance benefit of the patch.

However, all this is still in my stack of things to do, and I had not much
time in the Fall for that. I may have more time in the coming weeks. I'm fine
if things are updated and performance figures are collected in between, I'll
take it from where it is when I have time, if something remains to be done.

--
Fabien.

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