Re: why does this query not use a parallel query

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Dave Cramer <davecramer(at)gmail(dot)com>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: why does this query not use a parallel query
Date: 2018-03-02 16:44:40
Message-ID: 30033.1520009080@sss.pgh.pa.us
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Dave Cramer <davecramer(at)gmail(dot)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

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