Re: Combination of ordered-set aggregate function terminates JDBC connection on PostgreSQL 9.6.5

I wrote:
> Thinking about it more clearly, if a transition function is being run
> on behalf of several different Aggrefs (with identical input states),
> then no, the transition function should not care which Aggref it
> looks at. As you say it mustn't do anything different on the basis of
> the finalfn-related fields. The problem occurs when a finalfn calls
> AggGetAggref --- then, I think that the finalfn is entirely entitled
> to expect that it will see its own Aggref, not some other one that
> happens to share input+transition.

Concretely, I think we need to do the attached. This seems like
a bug fix to me, so I'm inclined to back-patch it. In the back
branches we could put the extra AggState field at the end, to
minimize ABI-break hazards.

BTW ... I was quite surprised to notice that the aggdirectargs
are treated as a property that has to be matched in order to
combine transition states. They aren't used during the transition
phase, so this seems like a pointless constraint. We could move
the aggdirectargs ExprState list to AggStatePerAggData and treat
the aggdirectargs as part of the finalfn-related data, instead.
As long as we're not merging states at all for OSAs, this is
moot, but it seems like something to fix along with that.

regards, tom lane