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Re: read block size

From: Michael Stone <mstone+postgres(at)mathom(dot)us>
To: John A Meinel <john(at)arbash-meinel(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: read block size
Date: 2005-06-28 17:27:01
Message-ID: 20050628172701.GW9591@mathom.us (view raw or flat)
Thread:
Lists: pgsql-performance
On Tue, Jun 28, 2005 at 12:02:55PM -0500, John A Meinel wrote:
>There has been discussion about changing the reading/writing code to be
>able to handle multiple pages at once, (using something like vread())
>but I don't know that it has been implemented.

that sounds promising

>Also, this would hurt cases where you can terminate as sequential scan
>early. 

If you're doing a sequential scan of a 10G file in, say, 1M blocks I
don't think the performance difference of reading a couple of blocks
unnecessarily is going to matter.

>And if the OS is doing it's job right, it will already do some
>read-ahead for you.

The app should have a much better idea of whether it's doing a
sequential scan and won't be confused by concurrent activity. Even if
the OS does readahead perfectly, you'll still get a with with larger
blocks by cutting down on the syscalls.

Mike Stone


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