linux-kernel - Re: [sqlite] light weight write barriers

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Date:	Mon, 12 Nov 2012 22:37:39 -0500
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Howard Chu <hyc@...as.com>
CC:	General Discussion of SQLite Database <sqlite-users@...ite.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Vladislav Bolkhovitin <vst@...b.net>,
	Theodore Ts'o <tytso@....edu>, drh@...ci.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [sqlite] light weight write barriers


Howard Chu, on 11/01/2012 08:38 PM wrote:
> Alan Cox wrote:
>>> How about that recently preliminary infrastructure to send ORDERED commands
>>> instead of queue draining was deleted from the kernel, because "there's no
>>> difference where to drain the queue, on the kernel or the storage side"?
>>
>> Send patches.
>
> Isn't any type of kernel-side ordering an exercise in futility, since
> a) the kernel has no knowledge of the disk's actual geometry
> b) most drives will internally re-order requests anyway
> c) cheap drives won't support barriers

This is why it is so important for performance to use all storage capabilities. 
Particularly, ORDERED commands instead of trying to pretend be smarter, than the 
storage, doing queue draining.

Vlad
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