From: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Chris Travers <chris(dot)travers(at)adjust(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Re: Anyone have experience benchmarking very high effective_io_concurrency on NVME's? |
Date: | 2017-11-01 04:06:49 |
Message-ID: | CAMsr+YEbWaDqL9Lj5-EGXMtFY7eN-PGRSbwCQfRBmMSdsg=GWg@mail.gmail.com |
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On 1 November 2017 at 11:49, Andres Freund <andres(at)anarazel(dot)de> wrote:
> Right. It'd probably be good to be a bit more adaptive here. But it's
> hard to do with posix_fadvise - we'd need an operation that actually
> notifies us of IO completion. If we were using, say, asynchronous
> direct IO, we could initiate the request and regularly check how many
> blocks ahead of the current window are already completed and adjust the
> queue based on that, rather than jus tfiring off fadvises and hoping for
> the best.
In case it's of interest, I did some looking into using Linux's AIO
support in Pg a while ago, when chasing some issues around fsync
retries and handling of I/O errors.
It was a pretty serious dead end; it was clear that fsync support in
AIO is not only incomplete but inconsistent across kernel versions,
let alone other platforms.
But I see your name in the relevant threads, so you know that. To save
others the time, see:
* https://lwn.net/Articles/724198/
* https://lwn.net/Articles/671649/
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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