"Matt Magoffin" <postgresql.org at msqr.us> writes:
> I'm trying to plan out a migration from Postgres 8.1 to Postgres 8.3. We
> currently use Slony to replicate our database, and I understand we should
> be able to replicate from 8.1 into 8.3 as long as we have the same version
> of Slony installed in both databases.
>
> In 8.1 I have a table that uses a text column to store XML data, and in
> 8.3 we plan to turn that into an xml type column. I can migrate that data
> using pg_dump and pg_restore with the --data-only option.
>
> I was wondering if I could just set up replication between the 8.1
> database and 8.3 database, and have the data replicated directly from the
> text column in 8.1 into the xml column in 8.3.

I'd expect that to work OK, but with one pretty big "foot gun" in
play, namely the fact that the XML type does validation.  That
provides the risk that if you ever put invalid XML into the column in
the 8.1 database, the attempt to INSERT/UPDATE it on the 8.3 instance
will fail, and replication will fail (until/unless you delete the
offending tuples from sl_log_[12] by hand).  That would be a nice way
to really muss up the cluster.
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