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.
No, we don't have plans to do that. We will allow continuous logging so a tar backup plus this log will bring you up to current.
What about the future synchronous replication or clustering? Will this feature do what shadowing in IB/FB does? Cause I've met a couple of people that really love this feature and they cling to FB because of this.
Actually, what is needed is:
- an exact mirror at all times; - a very simple, straightforward, and fast way to failover;
done by software.
-- dave
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