From: Greg Smith <greg@2ndquadrant.com>
To: Marti Raudsepp <marti@juffo.org>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-performance@postgresql.org
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
Date: Sun, 07 Nov 2010 18:35:29 -0500
Message-ID: <4CD737C1.9070502@2ndquadrant.com> (raw)
In-Reply-To: <AANLkTimhNzer1TOEnL55P-Un9TPp8fAeyOzX09259RxN@mail.gmail.com>
References: <AANLkTi=n3zxiLNFhbpiN=JPQPwB=BhXf9iepw1KOEs8U@mail.gmail.com>
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<201011010010.28724.andres@anarazel.de>
<4CD472CC.80006@2ndquadrant.com>
<AANLkTinEAmKDz7x356bgX=-6x7zpjK3bB0hYAmKvYHB9@mail.gmail.com>
<4CD47FCD.6010106@2ndquadrant.com>
<AANLkTimhNzer1TOEnL55P-Un9TPp8fAeyOzX09259RxN@mail.gmail.com>
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@2ndQuadrant.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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To: pgsql-performance@postgresql.org
Cc: greg@2ndquadrant.com, marti@juffo.org, andres@anarazel.de
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
In-Reply-To: <4CD737C1.9070502@2ndquadrant.com>
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