| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Philip Semanchuk <philip(at)americanefficient(dot)com> |
| Cc: | Guillaume Lelarge <guillaume(at)lelarge(dot)info>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Michael Lewis <mlewis(at)entrata(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Understanding bad estimate (related to FKs?) |
| Date: | 2020-11-02 20:08:12 |
| Message-ID: | 741231.1604347692@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Philip Semanchuk <philip(at)americanefficient(dot)com> writes:
> The query I asked about in the original post of this thread has 13 relations in it. IIUC, that's 13! or > 6 billion possible plans. How did the planner pick one plan out of 6 billion? I'm curious, both for practical purposes (I want my query to run well) and also because it's fascinating.
The twenty-thousand-foot overview is
https://www.postgresql.org/docs/devel/planner-optimizer.html
and then ten-thousand-foot level is the planner README file,
and then you pretty much gotta start reading code. You could also dig
into various planner expository talks that people have given at PG
conferences. I don't have links at hand, but there have been several.
regards, tom lane
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