From: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
---|---|
To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Clock sweep not caching enough B-Tree leaf pages? |
Date: | 2014-04-17 19:44:21 |
Message-ID: | CAHyXU0xv-vzKt8A2zvtHQe_a88qZ+ccFUVHsV7+NcbXrKccRAQ@mail.gmail.com |
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On Thu, Apr 17, 2014 at 2:28 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
>
>
> On Thursday, April 17, 2014, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>>
>> yeah -- the thing is, we are already too spendy already on
>> supplemental write i/o (hint bits, visible bits, freezing, etc) and
>> likely not worth it to throw something else on the pile unless the
>> page is already dirty; the medium term trend in storage is that read
>> vs write performance is becoming increasingly asymmetric, particularly
>> on the random side so it's very unlikely to balance out.
>
> Guess I wasn't clear but I was thinking to read the page in, not do any
> writing, and do it in a asynchronous way to the process doing the evicting.
no -- I got you. My point was, that's a pure guess unless you base it
on evidence recorded on the page itself. Without that evidence,
(which requires writing) the operating is in a a better place to make
that guess so it's probably better to defer that decision.
merlin
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