Message-ID: <44488F7E.6060704@logix-tt.com>
Date: Fri, 21 Apr 2006 09:53:34 +0200
From: Markus Schaber <schabi@logix-tt.com>
Organization: Logical Tracking and Tracing International AG, Switzerland
User-Agent: Debian Thunderbird 1.0.7 (X11/20051017)
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To: Wu Fengguang <wfg@mail.ustc.edu.cn>
Cc: pgsql-performance@postgresql.org
Subject: Re: Introducing a new linux readahead framework
References: <20060421013826.GA5217@mail.ustc.edu.cn>
	<20060421043147.GV49405@pervasive.com>
	<20060421071511.GA4885@mail.ustc.edu.cn>
In-Reply-To: <20060421071511.GA4885@mail.ustc.edu.cn>
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Hi, Wu,

Wu Fengguang wrote:

>>>In adaptive readahead, the context based method may be of particular
>>>interest to postgresql users. It works by peeking into the file cache
>>>and check if there are any history pages present or accessed. In this
>>>way it can detect almost all forms of sequential / semi-sequential read
>>>patterns, e.g.
>>>	- parallel / interleaved sequential scans on one file
>>>	- sequential reads across file open/close
>>>	- mixed sequential / random accesses
>>>	- sparse / skimming sequential read
>>>
>>>It also have methods to detect some less common cases:
>>>	- reading backward
>>>	- seeking all over reading N pages

Gread news, thanks!

> This call will disable readahead totally for fd:
>         posix_fadvise(fd, any, any, POSIX_FADV_RANDOM);
> 
> This one will reenable it:
>         posix_fadvise(fd, any, any, POSIX_FADV_NORMAL);
> 
> This one will enable readahead _and_ set max readahead window to
> 2*max_readahead_kb:
>         posix_fadvise(fd, any, any, POSIX_FADV_SEQUENTIAL);

I think that this is an easy, understandable and useful interpretation
of posix_fadvise() hints.


Are there any rough estimates when this will get into mainline kernel
(if you intend to submit)?

Thanks,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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