Re: Visibility map and freezing

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/