On 2019-06-04 16:39:32 -0400, Dave Cramer wrote: > On Tue, 4 Jun 2019 at 16:30, Andres Freund <andres.freund@enterprisedb.com> > wrote: > > > There's also no reason that I am aware that binary outputs can't be > > > supported. > > > > Well, it *does* increase version dependencies, and does make replication > > more complicated, because type oids etc cannot be relied to be the same > > on source and target side. > > > I was about to agree with this but if the type oids change from source > to target you still can't decode the text version properly. Unless I > mis-understand something here ?
The text format doesn't care about oids. I don't see how it'd be a problem? Note that some people *intentionally* use different types from source to target system when logically replicating. So you can't rely on the target table's types under any circumstance.
I think you really have to use the textual type which we already write out (cf logicalrep_write_typ()) to call the binary input functions. And you can send only data as binary that's from builtin types - otherwise there's no guarantee at all that the target system has something compatible. And even if you just assumed that all extensions etc are present, you can't transport arrays / composite types in binary: For hard to discern reasons we a) embed type oids in them b) verify them. b) won't ever work for non-builtin types, because oids are assigned dynamically.
I figured arrays and UDT's would be problematic.
> > I think if we were to add binary output - and I think we should - we > > ought to only accept a patch if it's also used in core. > > > > Certainly; as not doing so would make my work completely irrelevant for my > purpose.
What I mean is that the builtin logical replication would have to use this on the receiving side too.
Got it, thanks for validating that the idea isn't nuts. Now I *have* to produce a POC.