Horton

Re: Seq scans roadmap

Jeff Davis <pgsql@j-davis.com>

View thread View on postgr.es
From: Jeff Davis <pgsql@j-davis.com>
To: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Luke Lonergan <LLonergan@greenplum.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Simon Riggs <simon@enterprisedb.com>, Zeugswetter Andreas ADI SD <ZeugswetterA@spardat.at>, "CK.Tan" <cktan@greenplum.com>
Date: 2007-05-15T17:25:35Z
Lists: pgsql-hackers 
On Tue, 2007-05-15 at 10:42 +0100, Heikki Linnakangas wrote:
> Luke Lonergan wrote:
> > 32 buffers = 1MB with 32KB blocksize, which spoils the CPU L2 cache
> > effect.
> > 
> > How about using 256/blocksize?
> 
> Sounds reasonable. We need to check the effect on the synchronized 
> scans, though.
> 

I am a little worried that there will be greater differences in position
as the number of scans increase. If we have only 8 buffers and several
scans progressing, will they all be able to stay within a few buffers of
eachother at any given time?

Also, with 8 buffers, that means each scan must report every 4 pages at
most (and maybe every page), which increases lock contention (the new
design Heikki and I discussed requires a lock every time a backend
reports its position).

Regards,
	Jeff Davis