Re: Asynchronous Append on postgres_fdw nodes.

On 10/5/20 11:35 AM, Etsuro Fujita wrote:
Hi,
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:

PLAN
====
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.

-- 
regards,
Andrey Lepikhov
Postgres Professional