Re: Visibility map and freezing

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Euler Taveira de Oliveira <euler(at)timbira(dot)com>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Gregory Stark <stark(at)enterprisedb(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Subject: Re: Visibility map and freezing
Date: 2009-01-22 19:27:44
Message-ID: 4978C8B0.9080504@enterprisedb.com
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Euler Taveira de Oliveira wrote:
> Simon Riggs escreveu:
>> On Tue, 2009-01-20 at 21:51 +0200, Heikki Linnakangas wrote:
>>
>>> Attached is a simple patch to only start skipping pages after 20
>>> consecutive pages marked as visible in the visibility map. This doesn't
>>> do any "look-ahead", so it will always scan the first 20 pages of a
>>> table before it starts to skip pages, and whenever there's even one page
>>> that needs vacuuming, the next 19 pages will also be vacuumed.
>>>
>>> We could adjust that figure 20 according to table size. Or by
>>> seq_page_cost/random_page_cost. But I'm leaning towards a simple
>>> hard-coded value for now.
>> Yes, sounds good. Can we stick to multiples of 2 as the OS readahead
>> does IIRC? So either 16 or 32. I'd go 32.
>>
> Agreed. And do it a constant (ALL_VISIBLE_VM_THRESHOLD?).

Okay-dokay. I committed this with the constant as a #define, at value 32.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

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