Re: Binary support for pgoutput plugin

Hi,

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 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.

Greetings,

Andres Freund