Shaun Thomas wrote: > I have a revised backup process that's coming out inconsistent, and I'm not > entirely sure why. I call > pg_start_backup(), tar.gz the contents elsewhere, then pg_stop_backup(). > Nothing crazy. Upon restore, > two of my tables report duplicate IDs upon executing my redaction scripts. > The "duplicate" records > ended up having different ctid's, suggesting the log replay was incomplete. > However, nothing in the > restore logs suggest this is the case, and either way, the database wouldn't > have come up if it were. > (right?)
Wrong. The database cannot check all data for consistency upon backup. For one, that would take way too long. > Now, the main difference, is that I'm doing the backup process on our > streaming replication node. The > backup process calls the pg_start_backup() function on the upstream provider, > backs up the local > content, then calls pg_stop_backup() on the upstream provider. In both cases, > it captures the > start/stop transaction log positions to grab all involved archived WAL files. > I already know the start > xlog position is insufficient, because those transaction logs may not have > replayed on the standby > yet, so I also grab 3xcheckpoint_timeout extra older files (before backup > start), just in case. > > So, I get no complaints of missing or damaged archive log files. Yet the > restore is invalid. I checked > the upstream, and those duplicate rows are not present; it's clearly the > backup that's at fault. I > remember having this problem a couple years ago, but I "fixed" it by working > filesystem snapshots into > the backup script. I can do that again, but it seems like overkill, honestly. If you backup the standby, then you won't have a backup_label file. You cannot restore a backup without that. Moreover, recovery needs a checkpoint/restartpoint to start. Restartpoints on the standby won't be the same as checkpoints on the primary, so I believe that even with the backup_label file you would not be able to restore the data. I'm not sure about the second point, maybe somebody can confirm or refute that. Yours, Laurenz Albe -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
