Re: Parallel Aggregate

On Thu, Dec 10, 2015 at 10:42 PM, Haribabu Kommi
<kommi.haribabu@gmail.com> wrote:
>
> Here I attached a POC patch of parallel aggregate based on combine
> aggregate patch. This patch contains the combine aggregate changes
> also. This patch generates and executes the parallel aggregate plan
> as discussed in earlier threads.

I tried this out using PostGIS with no great success. I used a very
simple aggregate for geometry union because the combine function is
just the same as the transfer function for this case (I also mark
ST_Area() as parallel safe, so that the planner will attempt to
parallelize the query)..
 CREATE AGGREGATE ST_MemUnion (  basetype = geometry,  sfunc = ST_Union,  cfunc = ST_Union,  stype = geometry );

Unfortunately attempting a test causes memory corruption and death.
 select riding, st_area(st_memunion(geom)) from vada group by riding;

The explain looks OK:
                                     QUERY PLAN
---------------------------------------------------------------------------------------Finalize HashAggregate
(cost=220629.47..240380.26rows=79 width=1189)  Group Key: riding  ->  Gather  (cost=0.00..807.49 rows=8792 width=1189)
     Number of Workers: 1        ->  Partial HashAggregate  (cost=220628.59..220629.38 rows=79
 
width=1189)              Group Key: riding              ->  Parallel Seq Scan on vada  (cost=0.00..806.61
rows=8792 width=1189)

But the run dies.

NOTICE:  SRID value -32897 converted to the officially unknown SRID value 0
ERROR:  Unknown geometry type: 2139062143 - Invalid type

From the message it looks like geometry gets corrupted at some point,
causing a read to fail on very screwed up metadata.

P.