David Garamond wrote:
Is there a feature similar to this currently in Postgres, or will there be? Sometimes (like in a shared hosting environment), we cannot have the luxury of hot-swapped RAID or expensive SAN, and it's nice to be able to have a synchronous backup so that in case a disk fails, we can recover to the last moment just before failure.
Will PITR offer this?
Pitr recovers from the last moment before failure. Not sure what shadowing is.
Sorry, should've at least described 'shadowing'. A shadow is a synchronous page-level (I think) mirror file. That is, when you open a database /disk1/dbname.fdb and then issue a:
> CREATE SHADOW 1 '/disk2/dbname.fdb'; > CREATE SHADOW 2 '/disk3/dbname.fdb';
then all 3 files will be kept synchronized at all times. Each subsequent page write will go to all 3 files (if any of the write fails, the transaction fails, so it's not unlike a synchronous replication).
Now suppose /disk1 fails, one of the shadow can be configured to immediately take over as the master database, without any down time. We can then add /disk4/dbname.fdb, for instance, to become a new shadow.
Alternatively, when a shadow fails, IB/Firebird can refuse further transactions until there is another shadow coming up, so the database is shadowed all the time.
-- dave
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