From: | Greg Smith <greg(at)2ndquadrant(dot)com> |
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To: | Marti Raudsepp <marti(at)juffo(dot)org> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1? |
Date: | 2010-11-07 23:35:29 |
Message-ID: | 4CD737C1.9070502@2ndquadrant.com |
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Lists: | pgsql-performance |
Marti Raudsepp wrote:
> I will grant you that the details were wrong, but I stand by the conclusion.
> I can state for a fact that PostgreSQL's default wal_sync_method
> varies depending on the <fcntl.h> header.
>
Yes; it's supposed to, and that logic works fine on some other
platforms. The question is exactly what the new Linux O_DSYNC behavior
is doing, in regards to whether it flushes drive caches out or not.
Until you've quantified which of the cases do that--which is required
for reliable operation of PostgreSQL--and which don't, you don't have
any data that can be used to draw a conclusion from. If some setups are
faster because they write less reliably, that doesn't automatically make
them the better choice.
--
Greg Smith 2ndQuadrant US greg(at)2ndQuadrant(dot)com Baltimore, MD
PostgreSQL Training, Services and Support www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books
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