Re: Unexpected page allocation behavior on insert-only tables

From: Michael Renner <michael(dot)renner(at)amd(dot)co(dot)at>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Unexpected page allocation behavior on insert-only tables
Date: 2010-05-16 00:24:36
Message-ID: 4BEF3B44.5010402@amd.co.at
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On 16.05.2010 02:16, Tom Lane wrote:
> Michael Renner<michael(dot)renner(at)amd(dot)co(dot)at> writes:
>> I've written a simple tool to generate traffic on a database [1], which
>> did about 30 TX/inserts per second to a table. Upon inspecting the data
>> in the table, I noticed the expected grouping of tuples which came from
>> a single backend to matching pages [2]. The strange part was that the
>> pages weren't completely filled but the backends seemed to jump
>> arbitrarily from one page to the next [3]. For the table in question
>> this resulted in about 10% wasted space.
>
> Which table would that be? The trigger-driven updates to "auction",
> in particular, would certainly guarantee some amount of "wasted" space.

Yeah, the auction table receives heavy updates and gets vacuumed regularly.

The behavior I showed was for the "bid" table, which only gets inserts
(and triggers the updates for the auction table).

best regards,
Michael

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