To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Simon Riggs <simon@2ndquadrant.com>, pgsql-patches@postgresql.org
Subject: Re: [HACKERS] Point in Time Recovery 
In-reply-to: <200407190314.i6J3EAJ07392@candle.pha.pa.us> 
References: <200407190314.i6J3EAJ07392@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
	message dated "Sun, 18 Jul 2004 23:14:10 -0400"
Date: Mon, 19 Jul 2004 00:54:13 -0400
Message-ID: <8886.1090212853@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Bruce Momjian <pgman@candle.pha.pa.us> writes:
> What is the process of logging to tape?  Ideally we could just do 'dd'
> to the tape drive in append mode;  however we need a way of signalling
> that we want to change tapes.

The reason we use a user-specifiable shell command for archiving is
so that we do not have to answer the above ;-).  It's the user's problem
to write a shell script that does things the way he wants.  He can make
it connect to /dev/tty and ask the operator to swap tapes, or whatever.

Personally I am very accustomed to Hewlett-Packard's disk-to-tape backup
program "fbackup", which allows you to provide a shell script to handle
exactly this sort of thing, and it's worked well for me for many years.

> I am asking to make sure we don't need a PITR pause mode that prevents
> WAL files from being archived but also prevents them from being
> recycled.

WAL files will not be recycled until the archiver daemon has set a .done
flag file for them, so I see no problem here.  (Note: I took out some
code in Simon's original patch that would start bleating on the basis
of totally unsupportable assumptions about long archival of a log
segment "ought to" take.)

			regards, tom lane