On Tue, 2008-07-22 at 18:37 +0200, Markus Wanner wrote:
> Simon Riggs wrote:
> > * Logical replication via transaction log
> > * Integration with synchronous replication
>
> I'm curious on what you mean by these two points. AFAIK you are speaking
> of "logical" replication for methods which don't rely on the internal
> storage format of the database, but instead replicate closer to the SQL
> level. But the transaction log (the XLOG for Postres, REDO log for
> Oracle, etc..) is certainly bound to the storage format, so I'd classify
> the log shipping approaches as "physical" replication. What is it you
> are talking about?
Reconstructing SQL from WAL, allowing logical apply. So yes, you're
right, the actual replication of the data from one node to another is
physical - its the final apply of the changes that is logical. So this
fits neatly with our commitment to put synchronous replication into
server.
It allows WAL to be used as the replication transport, which reduces the
impact of tracking changes via triggers. The presence of commit records
in the sequence can be used to parallelize the apply phase if required.
I'm proposing to put the mechanisms in place to allow WAL to be used by
other replication projects. Which turn out to be relatively small
changes to the main server.
-- Simon Riggs www.2ndQuadrant.comPostgreSQL Training, Services and Support
