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Re: PITR logging control program

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: PITR logging control program
Date: 2004-04-29 14:07:01
Message-ID: 200404291407.i3TE71J23867@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Alvaro Herrera wrote:
> On Thu, Apr 29, 2004 at 12:18:38AM -0400, Bruce Momjian wrote:
> 
> > OK, I looked over the code.  Basically it appears pg_arch is a
> > client-side program that copies files from pg_xlog to a specified
> > directory, and marks completion in a new pg_rlog directory.
> > 
> > The driving part of the program seems to be:
> > 
> >     while ( (n = read( xlogfd, buf, BLCKSZ)) > 0)
> >         if ( write( archfd, buf, n) != n)
> >             return false;
> > 
> > The program basically sleeps and when it awakes checks to see if new WAL
> > files have been created.
> 
> Is the API able to indicate a written but not-yet-filled WAL segment?
> So an archiver could copy the filled part, and refill it later.  This
> may be needed because a segment could take a while to be filled.

I couldn't figure that out, but I don't think it does.  It would have to
lock the WAL writes so it could get a good copy, I think, and I didn't
see that.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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