On 21 June 2012 01:06, Christopher Browne <cbbro...@gmail.com> wrote:
> I guess I'm not seeing the purpose to having the origin node id in the > WAL stream either. > > We have it in the Slony sl_log_* stream, however there is a crucial > difference, in that sl_log_* is expressly a shared structure. In > contrast, WAL isn't directly sharable; you don't mix together multiple > WAL streams. Unfortunately you do. That's really the core of how this differs from current Slony. Every change we make creates WAL records. Whether that is changes originating on the current node, or changes originating on upstream nodes that need to be applied on the current node. The WAL stream is then read and filtered for changes to pass onto other nodes. So we want to be able to filter out the applied changes to avoid passing them back to the original nodes. Having each record know the origin makes the filtering much simpler, so if its possible to do it efficiently then its the best design. It turns out to be the best way to do this so far known. There are other design however, as noted. In all cases we need the origin id in the WAL. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
