Re: Spilling hashed SetOps and aggregates to disk

David Fetter <david(at)fetter(dot)org> writes:
> On Tue, Jun 05, 2018 at 02:56:23PM +1200, David Rowley wrote:
>> True. Although not all built in aggregates have those defined.

> Just out of curiosity, which ones don't? As of
> 3f85c62d9e825eedd1315d249ef1ad793ca78ed4, pg_aggregate has both of
> those as NOT NULL.

NOT NULL isn't too relevant; that's just protecting the fixed-width
nature of the catalog rows. What's important is which ones are zero.

# select aggfnoid::regprocedure, aggkind from pg_aggregate where (aggserialfn=0 or aggdeserialfn=0) and aggtranstype = 'internal'::regtype;
aggfnoid | aggkind
------------------------------------------------------+---------
array_agg(anynonarray) | n
array_agg(anyarray) | n
string_agg(text,text) | n
string_agg(bytea,bytea) | n
json_agg(anyelement) | n
json_object_agg("any","any") | n
jsonb_agg(anyelement) | n
jsonb_object_agg("any","any") | n
percentile_disc(double precision,anyelement) | o
percentile_cont(double precision,double precision) | o
percentile_cont(double precision,interval) | o
percentile_disc(double precision[],anyelement) | o
percentile_cont(double precision[],double precision) | o
percentile_cont(double precision[],interval) | o
mode(anyelement) | o
rank("any") | h
percent_rank("any") | h
cume_dist("any") | h
dense_rank("any") | h
(19 rows)

Probably the ordered-set/hypothetical ones aren't relevant for this
issue.

Whether or not we feel like fixing the above "normal" aggs for this,
the patch would have to not fail on extension aggregates that don't
support serialization.

regards, tom lane