| From: | Euler Taveira de Oliveira <euler(at)timbira(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(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: | 2009-01-20 21:34:21 |
| Message-ID: | 4976435D.6020706@timbira.com |
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| Lists: | pgsql-hackers |
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?).
--
Euler Taveira de Oliveira
http://www.timbira.com/
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