Subject: Re: [PATCHES] odd output in restore mode
From: Simon Riggs <simon@2ndquadrant.com>
To: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Martin Zaun <Martin.Zaun@Sun.COM>, Bruce Momjian <bruce@momjian.us>,
	Andrew Dunstan <andrew@dunslane.net>, Dave Page <dpage@pgadmin.org>,
	List pgsql-patches <pgsql-patches@postgresql.org>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
In-Reply-To: <48877AC0.7070603@enterprisedb.com>
References: <200807011520.m61FKhZ20311@momjian.us> <48867904.9090001@sun.com>
	<1216810783.3894.602.camel@ebony.2ndQuadrant>
	<48877AC0.7070603@enterprisedb.com>
Content-Type: text/plain
Date: Thu, 24 Jul 2008 00:05:56 +0100
Message-Id: <1216854356.3894.699.camel@ebony.2ndQuadrant>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit


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           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support