Re: checkpointer continuous flushing - V18

From: Andres Freund <andres(at)anarazel(dot)de>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: checkpointer continuous flushing - V18
Date: 2016-02-19 20:20:01
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On 2016-02-04 16:54:58 +0100, Andres Freund wrote:
> Hi,
> Fabien asked me to post a new version of the checkpoint flushing patch
> series. While this isn't entirely ready for commit, I think we're
> getting closer.
> I don't want to post a full series right now, but my working state is
> available on
> git:// checkpoint-flush

I've updated the git tree.

Here's the next two (the most important) patches of the series:
0001: Allow to trigger kernel writeback after a configurable number of writes.
0002: Checkpoint sorting and balancing.

For 0001 I've recently changed:
* Don't schedule writeback after smgrextend() - that defeats linux
delayed allocation mechanism, increasing fragmentation noticeably.
* Add docs for the new GUC variables
* comment polishing
* BackendWritebackContext now isn't dynamically allocated anymore

I think this patch primarily needs:
* review of the docs, not sure if they're easy enough to
understand. Some language polishing might also be needed.
* review of the writeback API, combined with the smgr/md.c changes.
* Currently *_flush_after can be set to a nonzero value, even if there's
no support for flushing on that platform. Imo that's ok, but perhaps
other people's opinion differ.

For 0002 I've recently changed:
* Removed the sort timing information, we've proven sufficiently that
it doesn't take a lot of time.
* Minor comment polishing.

I think this patch primarily needs:
* Benchmarking on FreeBSD/OSX to see whether we should enable the
mmap()/msync(MS_ASYNC) method by default. Unless somebody does so, I'm
inclined to leave it off till then.



Attachment Content-Type Size
0001-Allow-to-trigger-kernel-writeback-after-a-configurab.patch text/x-patch 37.3 KB
0002-Checkpoint-sorting-and-balancing.patch text/x-patch 15.9 KB

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