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Re: Half filled xlogs

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Magnus Hagander <mha(at)sollentuna(dot)net>
Cc: pgsql-hackers-win32(at)postgresql(dot)org
Subject: Re: Half filled xlogs
Date: 2005-03-20 23:09:03
Message-ID: 1111360143.11750.424.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers-win32
On Sun, 2005-03-20 at 17:02 +0100, Magnus Hagander wrote:
> >I'm looking into copying partially filled xlogs with the Archiver
> >process, to allow a more rounded warm standby database option.
> >
> >My understanding is that on win32, when an xlog file is still being
> >written to by a backend it will be locked and unable to be copied away
> >by another process.
> 
> No, that shouldn't be a problem. 

OK, good. That makes it a lot simpler.

I'll post a design that explains that soon.

> We open all our files with
> FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE (see port/open.c). It
> should work fine as the other process that reads it also opens it with
> at least FILE_SHARE_READ.

...but its the implications that count!

> To verify, I started up a backend and did a begin transaction;create
> table foo(bar int);
> Then I copied the xlog file, and it copied without any errors. 
> 
> AFAIK, it shuold also contain the actual data, as long as it's been
> synced (which would be the same on unix, right?). (or if the file is
> opened with o_dsync). I haven't verified it myself, though.

I was hoping to verify by theory - but I'll go for it then we can test.

Best Regards, Simon Riggs


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