Zeugswetter Andreas SB SD wrote:
>
> > As noted, one of the main problems is knowing where to begin
> > in the log. This can be handled by having backup processing
> > update the control file with the first lsn and log file
> > required. At the time of the backup, this information is or
> > can be made available. The control file can be the last file
> > added to the tar and can contain information spanning the entire
> > backup process.
>
> lsn and logfile number (of latest checkpoints) is already in the control
> file, thus you need control file at start of backup. (To reduce the number
> of logs needed for restore of an online backup you could force a checkpoint
> before starting file backup)
Maybe I should have been more clear. The control file snapshot must
be taken at backup start (as you mention) but can be stored in cache.
The fields can then be modified as we see fit. At the end of backup,
we can write this to a temp file and add it to the tar. Therefore,
as mentioned, the snapshot spans the entire backup process.
> You will also need lsn and logfile number after file backup, to know how much
> log needs to at least be replayed to regain a consistent state.
This is a nicety but not a necessity. If you have a backup end log
record, you just have to enforce that the PIT recovery encounters
that particular log record on forward recovery. Once encountered,
you know that you at passed the point of back up end.
Cheers,
Patrick