Re: Combining Aggregates

>
> > # explain analyze select a%1000000,length(string_agg(b,',')) from ab
> group
> > by 1;
> > QUERY PLAN
> >
> ---------------------------------------------------------------------------------------------------------------------------
> > GroupAggregate (cost=119510.84..144510.84 rows=1000000 width=32)
> (actual
> > time=538.938..1015.278 rows=1000000 loops=1)
> > Group Key: ((a % 1000000))
> > -> Sort (cost=119510.84..122010.84 rows=1000000 width=32) (actual
> > time=538.917..594.194 rows=1000000 loops=1)
> > Sort Key: ((a % 1000000))
> > Sort Method: quicksort Memory: 102702kB
> > -> Seq Scan on ab (cost=0.00..19853.00 rows=1000000 width=32)
> > (actual time=0.016..138.964 rows=1000000 loops=1)
> > Planning time: 0.146 ms
> > Execution time: 1047.511 ms
> >
> >
> > Patched
> > # explain analyze select a%1000000,length(string_agg(b,',')) from ab
> group
> > by 1;
> > QUERY PLAN
> >
> ------------------------------------------------------------------------------------------------------------------------
> > HashAggregate (cost=24853.00..39853.00 rows=1000000 width=32) (actual
> > time=8072.346..144424.872 rows=1000000 loops=1)
> > Group Key: (a % 1000000)
> > -> Seq Scan on ab (cost=0.00..19853.00 rows=1000000 width=32)
> (actual
> > time=0.025..481.332 rows=1000000 loops=1)
> > Planning time: 0.164 ms
> > Execution time: 263288.332 ms
>
> Well, that's pretty odd. I guess the plan change must be a result of
> switching the transition type from internal to text, although I'm not
> immediately certain why that would make a difference.
>

It is strange, why hashaggregate is too slow?

Pavel

>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>
>
> --
> Sent via pgsql-hackers mailing list (pgsql-hackers(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-hackers
>