Re: Asynchronous Append on postgres_fdw nodes.

From: "Andrey V(dot) Lepikhov" <a(dot)lepikhov(at)postgrespro(dot)ru>
To: Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>
Cc: Justin Pryzby <pryzby(at)telsasoft(dot)com>, "movead(dot)li" <movead(dot)li(at)highgo(dot)ca>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Asynchronous Append on postgres_fdw nodes.
Date: 2020-10-08 09:39:47
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On 10/5/20 11:35 AM, Etsuro Fujita wrote:
I found a small problem. If we have a mix of async and sync subplans
when we catch an assertion on a busy connection. Just for example:

Nested Loop (cost=100.00..174316.95 rows=975 width=8) (actual
time=5.191..9.262 rows=9 loops=1)
Join Filter: (frgn.a = l.a)
Rows Removed by Join Filter: 8991
-> Append (cost=0.00..257.20 rows=11890 width=4) (actual
time=0.419..2.773 rows=1000 loops=1)
Async subplans: 4
-> Async Foreign Scan on f_1 l_2 (cost=100.00..197.75
rows=2925 width=4) (actual time=0.381..0.585 rows=211 loops=1)
-> Async Foreign Scan on f_2 l_3 (cost=100.00..197.75
rows=2925 width=4) (actual time=0.005..0.206 rows=195 loops=1)
-> Async Foreign Scan on f_3 l_4 (cost=100.00..197.75
rows=2925 width=4) (actual time=0.003..0.282 rows=187 loops=1)
-> Async Foreign Scan on f_4 l_5 (cost=100.00..197.75
rows=2925 width=4) (actual time=0.003..0.316 rows=217 loops=1)
-> Seq Scan on l_0 l_1 (cost=0.00..2.90 rows=190 width=4)
(actual time=0.017..0.057 rows=190 loops=1)
-> Materialize (cost=100.00..170.94 rows=975 width=4) (actual
time=0.001..0.002 rows=9 loops=1000)
-> Foreign Scan on frgn (cost=100.00..166.06 rows=975
width=4) (actual time=0.766..0.768 rows=9 loops=1)

Reproduction script 'test1.sql' see in attachment. Here I force the
problem reproduction with setting enable_hashjoin and enable_mergejoin
to off.

'asyncmix.patch' contains my solution to this problem.

Andrey Lepikhov
Postgres Professional

Attachment Content-Type Size
test1.sql application/sql 1.3 KB
asyncmix.patch text/x-patch 2.8 KB

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