Re: asynchronous execution

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: robertmhaas(at)gmail(dot)com, amitdkhan(dot)pg(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: asynchronous execution
Date: 2017-03-13 02:33:00
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On 2017/03/11 8:19, Corey Huinker wrote:
> On Thu, Feb 23, 2017 at 6:59 AM, Kyotaro HORIGUCHI
> <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp <mailto:horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>>
> wrote:
> 9e43e87
> Patch fails on current master, but correctly applies to 9e43e87. Thanks
> for including the commit id.
> Regression tests pass.
> As with my last attempt at reviewing this patch, I'm confused about what
> kind of queries can take advantage of this patch. Is it only cases where a
> local table has multiple inherited foreign table children?

IIUC, Horiguchi-san's patch adds asynchronous capability for ForeignScan's
driven by postgres_fdw (after building some relevant infrastructure
first). The same might be added to other Scan nodes (and probably other
nodes as well) eventually so that more queries will benefit from
asynchronous execution. It may just be that ForeignScan's benefit more
from asynchronous execution than other Scan types.

> Will it work
> with queries where two foreign tables are referenced and combined with a

I think it will, because Append itself has been made async-capable by one
of the patches and UNION ALL uses Append. But as mentioned above, only
the postgres_fdw foreign tables will be able to utilize this for now.


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