Re: [PATCHES] odd output in restore mode

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Martin Zaun <Martin(dot)Zaun(at)Sun(dot)COM>, Bruce Momjian <bruce(at)momjian(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Dave Page <dpage(at)pgadmin(dot)org>, List pgsql-patches <pgsql-patches(at)postgresql(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCHES] odd output in restore mode
Date: 2008-07-23 23:05:56
Message-ID: 1216854356.3894.699.camel@ebony.2ndQuadrant
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On Wed, 2008-07-23 at 21:38 +0300, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > On Tue, 2008-07-22 at 17:19 -0700, Martin Zaun wrote:
> >> 8. Unresolved question of implementing now/later a "cp" replacement
> >
> > The patch implements what's been agreed.
> >
> > I'm not rewriting "cp", for reasons already discussed.
> >
> > Not a comment to you Martin, but it's fairly clear that I'm not
> > maintaining this correctly for Windows. I've never claimed to have
> > tested this on Windows, and only included Windows related items as
> > requested by others. I need to make it clear that I'm not going to
> > maintain it at all, for Windows. If others wish to report Windows issues
> > then they can suggest appropriate fixes and test them also.
> Hmm. I just realized that replacing the "cp" command within pg_standby
> won't help at all. The problem is with the command that copies the files
> *to* the archivelocation that pg_standby polls, not with the copy
> pg_standby does from archivelocation to pg_xlog. And we don't have much
> control over that.
> We really need a more reliable way of detecting that a file has been
> fully copied. One simple improvement would be to check the xlp_magic
> field of the last page, though it still wouldn't be bullet-proof.
> Do the commands that preallocate the space keep the file exclusively
> locked during the copy? If they do, shouldn't we get an error in trying
> to run the restore copy command, and retry after the 1s sleep in
> RestoreWALFileForRecovery? Though if the archive location is a samba
> mount or something, I guess we can't rely on Windows-style exclusive
> locking.

With respect, I need to refer you back to the my last paragraph above.

Simon Riggs
PostgreSQL Training, Services and Support

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