On Wednesday, June 20, 2012 05:34:42 PM Kevin Grittner wrote: > Simon Riggs <si...@2ndquadrant.com> wrote: > > This is not transaction metadata, it is WAL record metadata > > required for multi-master replication, see later point.
> > We need to add information to every WAL record that is used as the > > source for generating LCRs. > If the origin ID of a transaction doesn't count as transaction > metadata (i.e., data about the transaction), what does? It may be a > metadata element about which you have special concerns, but it is > transaction metadata. You don't plan on supporting individual WAL > records within a transaction containing different values for origin > ID, do you? If not, why is it something to store in every WAL > record rather than once per transaction? That's not intended to be > a rhetorical question. Its definitely possible to store it per transaction (see the discussion around http://archives.postgresql.org/message- id/201206201605.43634.and...@2ndquadrant.com) it just makes the filtering via the originating node a considerably more complex thing. With our proposal you can do it without any complexity involved, on a low level. Storing it per transaction means you can only stream out the data to other nodes *after* fully reassembling the transaction. Thats a pitty, especially if we go for a design where the decoding happens in a proxy instance. Other metadata will not be needed on such a low level. I also have to admit that I am very hesitant to start developing some generic "transaction metadata" framework atm. That seems to be a good way to spend a good part of time in discussion and disagreeing. Imo thats something for later. > I think it's because you're still thinking > of the WAL stream as *the medium* for logical replication data > rather than *the source* of logical replication data. I don't think thats true. See the above referenced subthread for reasons why I think the origin id is important. 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