| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Craig Ringer <craig(at)2ndquadrant(dot)com>, Roger Pack <rogerdpack2(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: feature request: explain "with details" option |
| Date: | 2016-09-12 20:25:19 |
| Message-ID: | 14917.1473711919@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I think the only part of this that would be really brutal to try to
> represent is alternative join orders. I see no reasonable way for
> EXPLAIN to output useful information about what other join orders were
> considered and why they were not chosen; the only thing that seems
> like it would help in that case would be an easy way to force the
> exact join order you want and then see what the plan looks like.
That exists today: write your query as a nest of explicit JOIN syntax
and set join_collapse_limit = 1. Not sure that it's really all that
useful, though.
regards, tom lane
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