Horton

Re: Avoiding OOM in a hash join with many duplicate inner keys

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, David Hinkle <hinkle@cipafilter.com>
Date: 2017-02-16T19:37:38Z
Lists: pgsql-hackers 
On Thu, Feb 16, 2017 at 11:11 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> I do think that's worrying, but on the other hand it seems like this
> solution could disable many hash joins that would actually be fine.  I
> don't think the largest ndistinct estimates we ever generate are very
> large, and therefore this seems highly prone to worry even when
> worrying isn't really justified.

+1. ndistinct has a general tendency to be wrong, owing to how ANALYZE
works, which we see problems with from time to time.


-- 
Peter Geoghegan

Commits

  1. Avoid out-of-memory in a hash join with many duplicate inner keys.