Re: Seq scans roadmap

Zeugswetter Andreas ADI SD wrote:
>> In reference to the seq scans roadmap, I have just submitted
>> a patch that addresses some of the concerns.
>>
>> The patch does this:
>>
>> 1. for small relation (smaller than 60% of bufferpool), use
>> the current logic 2. for big relation:
>> - use a ring buffer in heap scan
>> - pin first 12 pages when scan starts
>> - on consumption of every 4-page, read and pin the next 4-page
>> - invalidate used pages of in the scan so they do not
>> force out other useful pages
>
> A few comments regarding the effects:
>
> I do not see how this speedup could be caused by readahead, so what are
> the effects ?

I was wondering that as well. We'd really need to test all the changes
separately to see where the improvements are really coming from.

Also, that patch doesn't address the VACUUM issue at all. And using a
small fixed size ring with scans that do updates can be devastating. I'm
experimenting with different ring sizes for COPY at the moment. Too
small ring leads to a lot of WAL flushes, it's basically the same
problem we have with VACUUM in CVS HEAD.

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