Re: shadowing (like IB/Firebird)

Bruce Momjian wrote:
>>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