Hi, On Tuesday, June 19, 2012 08:03:04 AM Tom Lane wrote: > Andres Freund <and...@2ndquadrant.com> writes: > > On Monday, June 18, 2012 11:51:27 PM Daniel Farina wrote: > >> What's the cost of going a lot higher? Because if one makes enough > >> numerical space available, one can assign node identities without a > >> coordinator, a massive decrease in complexity. > > > > It would increase the size of every wal record. We just have 16bit left > > there by chance... > > "Every WAL record"? Why in heck would you attach it to every record? > Surely putting it in WAL page headers would be sufficient. We could > easily afford to burn a page switch (if not a whole segment switch) > when changing masters. The idea is that you can have cascading, circular and whatever replication topologies if you include the "logical origin" of a wal causing action into it. That is, if you have nodes A(1) and B(2) and a insert happens on A the wal records generated by that will get an xl_origin_id = 1 and when it will be decoded and replayed on B it will *also* get the id 1. Only when a change originally is generated on Bit will get xl_origin_id = 2. That way you can easily have circular or hierarchical replication topologies including diamonds.
> I'm against the idea of eating any spare space we have in WAL record > headers for this purpose, anyway; there are likely to be more pressing > needs in future. Every other solution to allowing this seems to be far more complicated than this, thats why I arrived at the conclusion that its a good idea. Greetings, Andres -- Andres Freund 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
