Message-ID: <1115776922.4281679a8e67f@webmail.telus.net>
Date: Tue, 10 May 2005 19:02:02 -0700
From: Mischa Sandberg <mischa.sandberg@telus.net>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: pgsql-general@postgresql.org
Subject: Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL
References: <200505110151.j4B1pnt16211@candle.pha.pa.us>
In-Reply-To: <200505110151.j4B1pnt16211@candle.pha.pa.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
User-Agent: Internet Messaging Program (IMP) 3.1-cvs

Quoting Bruce Momjian <pgman@candle.pha.pa.us>:

> 
> Is there a TODO anywhere in this discussion?  If so, please let me
> know.
> 

Umm... I don't think so. I'm not clear on what TODO means yet. 'Up for
consideration'?  If a "TODO" means committing to do, I would prefer to
follow up on a remote-schema (federated server) project first.
...

> > If there were room for improvement, (and I didn't see it in the
> source)
> > it would be the logic to:
> > 
> > - swap inner and outer inputs (batches) when the original inner
> turned
> > out to be too large for memory, and the corresponding outer did
> not. If
> > you implement that anyway (complicates the loops) then it's no
> trouble
> > to just hash the smaller of the two, every time; saves some CPU.
> > 
> > - recursively partition batches where both inner and outer input
> batch
> > ends up being too large for memory, too; or where the required
> number of
> > batch output buffers alone is too large for working RAM. This is
> only
> > for REALLY big inputs.
> > 
> > Note that you don't need a bad hash function to get skewed batch
> sizes;
> > you only need a skew distribution of the values being hashed.