From: | Michael Paquier <michael(at)paquier(dot)xyz> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Antonin Houska <ah(at)cybertec(dot)at>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Attempt to consolidate reading of XLOG page |
Date: | 2019-11-25 03:30:48 |
Message-ID: | 20191125033048.GG37821@paquier.xyz |
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Lists: | pgsql-hackers |
On Fri, Nov 22, 2019 at 07:56:32PM -0300, Alvaro Herrera wrote:
> I see no reason to leave ws_off. We can move that to XLogReaderState; I
> did that here. We also need the offset in WALReadError, though, so I
> added it there too. Conceptually it seems clearer to me this way.
Yeah, that seems cleaner.
> What do you think of the attached?
Looks rather fine to me.
> BTW I'm not clear what errors can pread()/pg_pread() report that do not
> set errno. I think lines 1083/1084 of WALRead are spurious now.
Because we have no guarantee that errno will be cleared if you do a
partial read where errno is not set, so you may finish by reporting
the state of a previous failed read instead of the partially-failed
one depending on how WALReadError is treated? In short, I don't see
any actual reason why it would be good to remove the reset of errno
either before the calls to pread and pwrite().
--
Michael
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