Re: Error from array_agg when table has many rows

On Sun, 9 Mar 2025 at 04:50, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Richard Guo <guofenglinux@gmail.com> writes:
> > We are performing deserialization during the final phase of the
> > aggregation on data of type RECORD but we fail to provide a valid
> > typmod (array_agg_deserialize() uses -1 as the typmod when calling the
> > receiveproc).
>
> > I haven't verified it, but I suspect it's related to 16fd03e95.
>
> Yeah.  I don't think there is any way for array_agg_deserialize to
> know the correct typmod, so what we have to do is disable using
> partial aggregation in this case.  Fortunately there's a
> policy-setting function that can be taught that, as attached.

The only way I can think of to get that would be to special-case
array_agg_serialize() to have it serialize the typmod when the send
function is record_send(), then add a similar special-case to
array_agg_deserialize() to check for a record_recv() and deserialize
the typmod there. That doesn't seem very pretty, so I'm happy to go
with your fix to disable parallel aggregates for this case.

David