Re: empty backup_label

On Tue, Jun 26, 2012 at 05:33:42PM +0200, Magnus Hagander wrote:
- On Tue, Jun 26, 2012 at 5:24 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
- > On Sun, Jun 24, 2012 at 5:33 PM, David Kerr <dmk(at)mr-paradox(dot)net> wrote:
- >> Howdy,
- >>
- >> We're using NetApp's flexclone's whenever we need to move our DB between machines.
- >>
- >> One specific case where we do that is when we're creating a new streaming replication target.
- >>
- >> The basic steps we're using are:
- >> pg_start_backup();
- >> <flex clone within the netapp>
- >> pg_stop_backup();
- >>
- >> The problem i'm seeing is that periodically the backup_label is empty, which means
- >> I can't start the new standby.
- >>
- >> I believe that since the NetApp stuff is all happening within the SAN this file hasn't been
- >> fsynced to disk by the time we take the snapshot.
- >>
- >> One option would be to do a "sync" prior to the clone, however that seems kind of like a
- >> heavy operation, and it's slightly more complicated to script. (having to have a user
- >> account on the system to sudo rather than just connecting to the db to issue the
- >> pg_start_backup(...) )
- >>
- >> Another option is to add pg_fsync(fileno(fp)) after the fflush() when creating the file (I'm not
- >> sure if fsync implies fflush or not, if it does you could just replace it.)
- >>
- >> I think this type of snapshot is fairly common, I've been doing them since 2000 with EMC,
- >> i'm sure that most SAN vendors support it.
- >
- > These seems like a good idea to me.  Actually, I'm wondering if we
- > shouldn't back-patch this.
- >
- > Thoughts?
-
- Certainly can't hurt.
-
- I guess any other files that are lost this way will be recreated by
- WAL recovery - or is there something else tha tmight be of risk of
- similar treatment?

The only other file I've run into is pgstats.stat, which I think is ok to get blown away.
There certianly could be others though.

Dave