|From:||Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>|
|To:||Antonin Houska <ah(at)cybertec(dot)at>|
|Cc:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, pgsql-hackers(at)postgresql(dot)org|
|Subject:||Re: Problems with plan estimates in postgres_fdw|
|Views:||Raw Message | Whole Thread | Download mbox|
(2019/03/26 21:41), Etsuro Fujita wrote:
> (2019/03/20 20:47), Etsuro Fujita wrote:
>> Attached is an updated version of the patch set.
> One thing I noticed while self-reviewing the patch for UPPERREL_FINAL
> is: the previous versions of the patch don't show EPQ plans in EXPLAIN,
> as shown in the below example, so we can't check if those plans are
> constructed correctly, which I'll explain below:
> In HEAD, this test case checks that a Result node is inserted atop of an
> EPQ plan for a foreign join (if necessary) when the foreign join is at
> the topmost join level (see discussion ), but the patched version
> doesn't show EPQ plans in EXPLAIN, so we can't check that as-is. Should
> we show EPQ plans in EXPLAIN? My inclination would be to not show them,
> because that information would be completely useless for the user.
In addition to the above reason, it would be waste of cycles to create
the no-longer-needed EPQ plans to only show them in EXPLAIN, so I kept
the patch as-is.
> Another thing I noticed is: the previous versions make pointless another
> test case added by commit 4bbf6edfb (and adjusted by commit 99f6a17dd)
> that checks an EPQ plan constructed from multiple merge joins, because
> they changed a query plan for that test case like the above. (Actually,
> though, that test case doesn't need that EPQ plan already since it
> doesn't involve regular tables and it never fires EPQ rechecks.) To
> avoid that, I modified that test case accordingly.
Attached is an updated version of the patchset. I did that test case
modification in a separate patch (see the 0002 patch in the attached).
I also added a bit more assertions and added/tweaked some comments.
I'll check the patchset once more and add the commit messages in the
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