Re: ParallelFinish-hook of FDW/CSP (Re: Steps inside ExecEndGather)

From: Kohei KaiGai <kaigai(at)kaigai(dot)gr(dot)jp>
To: Claudio Freire <klaussfreire(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: ParallelFinish-hook of FDW/CSP (Re: Steps inside ExecEndGather)
Date: 2017-02-25 04:30:32
Message-ID: CADyhKSUB6f+22LtBBqBfaROv-X8JU9DZLsDBeaNU9+fEbCqojA@mail.gmail.com
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2017-02-25 1:40 GMT+09:00 Claudio Freire <klaussfreire(at)gmail(dot)com>:
> On Fri, Feb 24, 2017 at 1:24 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Fri, Feb 24, 2017 at 7:29 PM, Kohei KaiGai <kaigai(at)kaigai(dot)gr(dot)jp> wrote:
>>> This attached patch re-designed the previous v2 according to Robert's comment.
>>> All I had to do is putting entrypoint for ForeignScan/CustomScan at
>>> ExecShutdownNode,
>>> because it is already modified to call child node first, earlier than
>>> ExecShutdownGather
>>> which releases DSM segment.
>>
>> Aside from the documentation, which needs some work, this looks fine
>> to me on a quick read.
>
> LGTM too.
>
> You may want to clarify in the docs when the hook is called in
> relation to other hooks too.
>
I tried to add a description how custom-scan callbacks performs under the
executor, and when invoked roughly.
However, it is fundamentally not easy for most of people because it assumes
FDW/CSP author understand the overall behavior of optimizer / executor, not
only APIs specifications.

Thanks,
--
KaiGai Kohei <kaigai(at)kaigai(dot)gr(dot)jp>

Attachment Content-Type Size
parallel-finish-fdw_csp.v4.patch application/octet-stream 8.2 KB

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