| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] <> join selectivity estimate question |
| Date: | 2017-11-30 15:05:31 |
| Message-ID: | CA+TgmoaEyCkxUj3Ytm11+7mzE2zrhx6-cb_-Jo_=vPRQQWJxng@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Nov 29, 2017 at 11:55 PM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> Thank you for the original pointer and the commit. Everything here
> seems to make intuitive sense and the accompanying throw-away tests
> that I posted above seem to produce sensible results except in some
> cases that we discussed, so I think this is progress. There is still
> something pretty funny about the cardinality estimates for TPCH Q21
> which I haven't grokked though. I suspect it is crafted to look for a
> technique we don't know (an ancient challenge set by some long retired
> database gurus back in 1992 that their RDBMSs know how to solve,
> hopefully not in the manner of a certain car manufacturer's air
> pollution tests), but I haven't yet obtained enough round tuits to dig
> further. I will, though.
Hmm, do you have an example of the better but still-funky estimates
handy? Like an EXPLAIN plan?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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