On 24.04.2013 10:57, Simon Riggs wrote:
On 24 April 2013 08:23, Heikki Linnakangas<hlinnakan...@vmware.com>  wrote:
On 22.04.2013 18:44, Simon Riggs wrote:

On 22 April 2013 09:29, Heikki Linnakangas<hlinnakan...@vmware.com>

Hmm. That requires write access to $DATADIR, so that's not quite the same
thing as the trigger_file recovery.conf option.

Well, you also (elsewhere) requested that we must keep recovery.conf
in $DATADIR, so it needs to be writable.

That's a slightly different requirement. $DATADIR must be writable by the
process that restores the backup or puts the server into standby mode, while
trigger_file needs to be writable by the process that triggers failover.
Those are not necessarily the same thing. I'm thinking of a heartbeat
process that triggers failover by creating a file on an NFS server or
similar. Possibly the same location where the WAL archive is located.
$DATADIR would be stored elsewhere.

The default you've requested is fast promotion and I've agreed to that.

The ability to write a file called "promote" to $DATADIR is there as a
protection in case we need it in the field, its not going to be the
primary mechanism any more. So if you're not intending to use it ever,
it doesn't seem worth discussing the fact you don't like its location.

Ok, works for me.

But if you do want to discuss it, I think it's unreasonable of you to
demand recovery.conf cannot be outside $DATADIR and then also demand
related files be relocatable outside $DATADIR as well, the exact
opposite. We had the chance to avoid making $DATADIR writable
externally and that's gone now, at least for now.

As I said above, it's a different situation. recovery.conf has always been in $DATADIR, and it's always been possible to point trigger_file elsewhere, and you've always gotten full functionality using the trigger_file. I just want to maintain that status quo. Which your patch achieves, so I'm happy that that.

Here's the patch I was intending to apply. Please let me know if you
have comments.

Regarding the change in pg_ctl:

-        * Use two different kinds of promotion file so we can understand
-        * the difference between smart and fast promotion.
+        * For 9.3 onwards, use fast promotion as the default option.
+        * Promotion with a full checkpoint is still possible by writing
+        * a file called "promote", e.g.
+        *       snprintf(promote_file, MAXPGPATH, "%s/promote", pg_data);
-       if (shutdown_mode >= FAST_MODE)
-               snprintf(promote_file, MAXPGPATH, "%s/fast_promote", pg_data);
-       else
-               snprintf(promote_file, MAXPGPATH, "%s/promote", pg_data);
+       snprintf(promote_file, MAXPGPATH, "%s/fast_promote", pg_data);

Should there be a version check there? I guess we've never guaranteed a newer pg_ctl to work with an older server version, but it seems likely that someone would try to do that, especially with "pg_ctl promote". With the above change, creating $DATADIR/fast_promote in a 9.2 server's data dir will do nothing. I'd suggest that we keep the filename unchanged, "promote", and only change the behavior in the server side, so that it performs fast promotion. If you want to have a "slow" promote file, we can call that "slow_promote" or "checkpoint_then_promote" or something.

Aside from that, I assume you'll clean up the now-dead -m fast option etc.

- Heikki

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