On Thu, Dec 10, 2015 at 10:42 PM, Haribabu Kommi
<kommi.harib...@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)..

   basetype = geometry,
   sfunc = ST_Union,
   cfunc = ST_Union,
   stype = geometry

Unfortunately attempting a test causes memory corruption and death.

  select riding,
  from vada group by riding;

The explain looks OK:

                                      QUERY PLAN
 Finalize HashAggregate  (cost=220629.47..240380.26 rows=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
               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.


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