Обсуждение: why does this query not use a parallel query

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why does this query not use a parallel query

От
Dave Cramer
Дата:
Have a query:

explain analyze SELECT minion_id FROM mob_player_mob_118 WHERE player_id = 55351078;
                                                                             QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Index Only Scan using mob_player_mob_118_pkey on mob_player_mob_118  (cost=0.44..117887.06 rows=4623076 width=4) (actual time=0.062..3716.105 rows=4625123 loops=1)
   Index Cond: (player_id = 55351078)
   Heap Fetches: 1152408
 Planning time: 0.241 ms
 Execution time: 5272.171 ms

If I just get the count it will use a parallel query

explain analyze SELECT count(minion_id) FROM mob_player_mob_118 WHERE player_id = 55351078;

Thanks

Dave Cramer

Re: why does this query not use a parallel query

От
Tom Lane
Дата:
Dave Cramer <davecramer@gmail.com> writes:
> Have a query:
> explain analyze SELECT minion_id FROM mob_player_mob_118 WHERE player_id =
> 55351078;

>  Index Only Scan using mob_player_mob_118_pkey on mob_player_mob_118
> (cost=0.44..117887.06 rows=4623076 width=4) (actual time=0.062..3716.105
> rows=4625123 loops=1)

I don't think we have parallel IOS yet (I might be wrong).  If so,
it probably thinks this is cheaper than the best available parallel plan.

> If I just get the count it will use a parallel query

Likely a parallelized aggregation.

            regards, tom lane