Re: Proposed Patch to Improve Performance of Multi-Batch Hash Join for Skewed Data Sets

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Joshua Tolley <eggyknap(at)gmail(dot)com>
Cc: "Lawrence, Ramon" <ramon(dot)lawrence(at)ubc(dot)ca>, pgsql-hackers(at)postgresql(dot)org, Bryce Cutt <pandasuit(at)gmail(dot)com>
Subject: Re: Proposed Patch to Improve Performance of Multi-Batch Hash Join for Skewed Data Sets
Date: 2008-11-05 15:20:41
Message-ID: 14295.1225898441@sss.pgh.pa.us
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Joshua Tolley <eggyknap(at)gmail(dot)com> writes:
> On Mon, Oct 20, 2008 at 03:42:49PM -0700, Lawrence, Ramon wrote:
>> We propose a patch that improves hybrid hash join's performance for large
>> multi-batch joins where the probe relation has skew.

> I also recommend modifying docs/src/sgml/config.sgml to include the
> enable_hashjoin_usestatmcvs option.

If the patch is actually a win, why would we bother with such a GUC
at all?

regards, tom lane

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