Re: Block level parallel vacuum WIP

On 23.08.2016 15:41, Michael Paquier wrote:
> On Tue, Aug 23, 2016 at 8:02 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>> As for PoC, I implemented parallel vacuum so that each worker
>> processes both 1 and 2 phases for particular block range.
>> Suppose we vacuum 1000 blocks table with 4 workers, each worker
>> processes 250 consecutive blocks in phase 1 and then reclaims dead
>> tuples from heap and indexes (phase 2).
> So each worker is assigned a range of blocks, and processes them in
> parallel? This does not sound performance-wise. I recall Robert and
> Amit emails on the matter for sequential scan that this would suck
> performance out particularly for rotating disks.

Rotating disks is not a problem - you can always raid them and etc. 8k 
allocation per relation  once per half an hour that is the problem. Seq 
scan is this way = random scan...


Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company