From: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: postgres_fdw bug in 9.6 |
Date: | 2016-12-16 12:50:45 |
Message-ID: | f2684b07-b2e2-155b-b1e8-e141e89458b5@lab.ntt.co.jp |
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Lists: | pgsql-hackers |
On 2016/12/16 11:25, Etsuro Fujita wrote:
> As I said upthread, an alternative I am thinking is (1) to create an
> equivalent nestloop join path using inner/outer paths of a foreign join
> path, except when that join path implements a full join, in which case a
> merge/hash join path is used, (2) store it in fdw_outerpath as-is, and
> (3) during an EPQ recheck, apply postgresRecheckForeignScan to the outer
> subplan created from the fdw_outerpath as-is. What do you think about
> that?
Let me explain about #1 and #2 a bit more. What I have in mind is:
* modify postgresGetForeignPaths so that a simple foreign table scan
path is stored into the base relation's PgFdwRelationInfo.
* modify postgresGetForeignJoinPaths so that
(a) a local join path for a 2-way foreign join is created using
simple foreign table scan paths stored in the base relations'
PgFdwRelationInfos, and stored into the join relation's PgFdwRelationInfo.
(b) a local join path for a 3-way foreign join, whose left input is
a 2-way foreign join, is created using a local join path stored in the
left input join relation's PgFdwRelationInfo and a simple foreign table
scan path stored into the right input base relation's PgFdwRelationInfo.
(c) Likewise for higher level foreign joins.
(d) local join paths created are passed to create_foreignscan_path
and stored into the fdw_outerpaths of the resulting ForeignPahts.
I think that that would need special handling for foreign joins with
sort orders; add an explicit sort to the local join paths, if needed.
I am thinking to provide a helper function that creates a local join
path for (a), (b), and (c).
Best regards,
Etsuro Fujita
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