From: Antonin Houska <ah@cybertec.at>
To: Andres Freund <andres@anarazel.de>,
    Michael Paquier <michael@paquier.xyz>, pgsql-hackers@postgresql.org,
    Alvaro Herrera <alvherre@2ndquadrant.com>
Subject: Re: 2pc leaks fds
In-reply-to: <26247.1586157152@antos>
References: <20200406025651.fpzdb5yyb7qyhqko@alap3.anarazel.de>
 <20200406052648.GB2066@paquier.xyz>
 <20200406054449.ssmrzj4fav3ewvaq@alap3.anarazel.de> <26247.1586157152@antos>
Comments: In-reply-to Antonin Houska <ah@cybertec.at>
   message dated "Mon, 06 Apr 2020 09:12:32 +0200."
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Date: Wed, 08 Apr 2020 09:26:37 +0200
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Antonin Houska <ah@cybertec.at> wrote:

> Andres Freund <andres@anarazel.de> wrote:
> > But I'm not sure it's quite the right idea. I'm not sure I fully
> > understand the design of 0dc8ead46, but it looks to me like it's
> > intended to allow users of the interface to have different ways of
> > opening files. If we just close() the fd that'd be a bit more limited.
> =

> It should have allowed users to have different ways to *locate the segme=
nt*
> file. The WALSegmentOpen callback could actually return file path instea=
d of
> the file descriptor and let WALRead() perform the opening/closing, but t=
hen
> the WALRead function would need to be aware whether it is executing in b=
ackend
> or in frontend (so it can use the correct function to open/close the fil=
e).

Well, #ifdef FRONTEND can be used to distinguish the caller of
WALRead(). However now that I tried to adjust the API, I see that
pg_waldump.c:WALDumpOpenSegment uses specific logic to open the file. So i=
f
the callback only returned the file name, there would be no suitable place=
 for
the things that WALDumpOpenSegment does.

-- =

Antonin Houska
Web: https://www.cybertec-postgresql.com