Re: Asynchronous Append on postgres_fdw nodes.

On Mon, Sep 28, 2020 at 10:35 AM Kyotaro Horiguchi
<horikyota.ntt@gmail.com> wrote:
> At Sat, 26 Sep 2020 19:45:39 +0900, Etsuro Fujita <etsuro.fujita@gmail.com> wrote in
> > Your patch (and the original patch by Robert [1]) modified
> > ExecAppend() so that it can process local plan nodes while waiting for
> > the results from remote queries, which would be also a feature that’s
> > not supported by Thomas’ patch, but I’d like to know performance
> > results.

> At least, even though theoretically, I think it's obvious that it's
> performant to do something than just sitting waitng for the next tuple
> to come from abroad.

I did a simple test on my laptop:

create table t1 (a int, b int, c text);
create foreign table p1 (a int, b int, c text) server server1 options
(table_name 't1');
create table p2 (a int, b int, c text);

insert into p1 select 10 + i % 10, i, to_char(i, 'FM00000') from
generate_series(0, 99999) i;
insert into p2 select 20 + i % 10, i, to_char(i, 'FM00000') from
generate_series(0, 99999) i;

analyze p1;
vacuum analyze p2;

create table pt (a int, b int, c text) partition by range (a);
alter table pt attach partition p1 for values from (10) to (20);
alter table pt attach partition p2 for values from (20) to (30);

set enable_partitionwise_aggregate to on;

select a, count(*) from pt group by a;

HEAD: 47.734 ms
With your patch: 32.400 ms

This test is pretty simple, but I think this shows that the mentioned
feature would be useful for cases where it takes time to get the
results from remote queries.

Cool!

Best regards,
Etsuro Fujita