Goulet, Dick wrote:
As an Oracle DBA primarily, moving more towards PostGreSQL as time passes, the "alter system switch logfile" command is very often used at the end of a hot backup to force a logfile switch and consequently provide a full archive log set. The command causes the database engine to cease using the current online redo log and have it archived to the archive log destination. This is the only way to be sure that all required archive logs are present in a backup to reconstitute the database at another location.
Dick Goulet Senior Oracle DBA Oracle Certified 8i DBA -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 06, 2004 5:36 PM To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: Re: [ADMIN] Multiple WALs for PITR ?
Michael Kleiser <[EMAIL PROTECTED]> wrote on 06.10.2004, 16:29:08: > I wan`t to use Point in Time Recovery > I allread read > http://developer.postgresql.org/docs/postgres/backup-online.html#BACKU > P-ARCHIVING-WAL >
Good!
> But I still wonder, if it is possible for PostgreSQL 8.0 to write > multiple, redundant WAL-Files like Oracles with its redo-log-groups ?
Not currently.
That was something I considered, though in the end lacked both implementation time and justification for.
If you can explain why you think that might be necessary, I'd be happy to consider it for v8.1.
RAID-10 seems a good solution for me...
I heared about some RAIDs saying "yes your data is on disk" to the oracle-database, but it wasn't so. So Oracle can't do a complete restore. The solution was to store the redo-log-files (=WALS) to local attached disk, but of course redundant on multiple disks. But other oracle-dba use RAIDs to store the redo-logs with no problems.
> > Is threre an equivalent to Oracles "ALTER SYSTEM SWITCH LOGFILE" ? >
Not currently.
Again, if you can say why we might want that, it can also be added - other than "they have it, so we want it too" :-)
In the online-backup-strategie described in http://developer.postgresql.org/docs/postgres/backup-online.html#BACKUP-ARCHIVING-WAL thre must be a special attention fir active WAL, if one want to backup it also. With "ALTER SYSTEM SWITCH LOGFILE" one could make it to a not active WAL. This would make it easier to backup it, especially if one want to use backups-programms like amanda. If there where multiple redundant WALs, one could compare them as a consistency-check. But this is only possible if nobody writes to the compared files.
This is a likely addition for 8.1, since we will most likely want to archive xlog files every N minutes, whatever the transaction rate, allowing people to specify a maximum period of data loss - but this seemed like an enhancement rather than a definite feature for 8.0
Great!
Regards Michael Kleiser
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