Re: 9.2.3 crashes during archive recovery

On Fri, Feb 15, 2013 at 3:49 PM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
>> While this solution would help solve my issue, it assumes that the
>> correct amount of WAL files are actually there. Currently the docs for
>> setting up a standby refer to "24.3.4. Recovering Using a Continuous
>> Archive Backup", and that step recommends emptying the contents of
>> pg_xlog. If this is chosen as the solution the docs should be adjusted
>> to recommend using pg_basebackup -x for setting up the standby.
>
> When the backup is taken using pg_start_backup or pg_basebackup,
> minRecoveryPoint is set correctly anyway, and it's OK to clear out pg_xlog.

How is minRecoveryPoint supposed to get set? I just tried taking a
pg_basebackup on master running pgbench. The resulting data dir
controlfile had this:

Min recovery ending location: 0/0

The end location was not in the backup_label either.

Looking at basebackup.c the process seems to be:
1. pg_start_backup
2. copy out backup_label
3. copy out rest of the datadir
4. copy out control file
5. pg_stop_backup
6. copy out WAL
7. send backup stop location

And pg_basebackup.c only uses the stop location to decide how much WAL to fetch.

I don't see anything here that could correctly communicate min
recovery point. Maybe I'm missing something.

> Yeah, it probably could use some editing, as the underlying code has evolved
> a lot since it was written. The suggestion to clear out pg_xlog seems like
> an unnecessary complication. It's safe to do so, if you restore with an
> archive, but unnecessary.
>
> The "File System Level Backup" chapter
> (http://www.postgresql.org/docs/devel/static/backup-file.html) probably
> should mention "pg_basebackup -x", too.
>
> Docs patches are welcome..

I will give it a shot.

Ants Aasma
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