On Wed, Nov 26, 2014 at 09:01:13PM -0500, Stephen Frost wrote: > * Alvaro Herrera (alvhe...@2ndquadrant.com) wrote: > > Bruce Momjian wrote: > > > How would replicating DDL handle cases where the master and slave > > > servers have different major versions and the DDL is only supported by > > > the Postgres version on the master server? > > > > Normally you would replicate between an older master and a newer > > replica, so this shouldn't be an issue. I find it unlikely that we > > would de-support some syntax that works in an older version: it would > > break pg_dump, for one thing.
I like the idea of older master/new replica, but what about bidirectional replication? Would the create/alter/drop WAL locical structure remain consistent across major versions, or would the code have to read at least one older version? Would we limit it to one? > While I tend to agree with you that it's not something we're likely to > do, how would it break pg_dump? We have plenty of version-specific > logic in pg_dump and we could certainly generate a different syntax in > a newer version than we did in an older version, if the newer server was > expecting something different. We've always held that you should use > the version of pg_dump which match the server you are moving *to*, after > all. pg_upgrade avoids having to deal with major version changes by leveraging pg_dump. Is it possible to have the new replica use the new pg_dump to connect to the old master to get a CREATE command that it can execute? Would that avoid having to ship CREATE syntax? What it wouldn't help with is ALTER and DROP though. (We do have ALTER but I think only for inheritance cases.) > > In other words I view cross-version replication as a mechanism to > > upgrade, not something that you would use permanently. Once you > > finish upgrading, promote the newer server and ditch the old master. > > I agree with this also. > > > If it would fail, does this limit the idea that logical replication > > > allows major version-different replication? > > > > Not in my view, at least. > > I'm all for having logical replication be a way to do major version > different replication (particularly for the purposes of upgrades), but > it shouldn't mean we can never de-support a given syntax. > > As one example, we've discussed a few times removing certain table-level > privileges on the basis that they practically mean you own the table. > Perhaps that'll never actually happen, but if it does, logical > replication would need to deal with it. Should we just tell the user not to modify the database schema during this period? Should we have a server mode which disables DDL? -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
