Re: Visibility map and freezing

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