Re: DELETE query and indexes again

On Thu, Jul 23, 2020 at 5:11 PM Wells Oliver <wells(dot)oliver(at)gmail(dot)com> wrote:

> This play_statistics table has 96,577,179 rows. Its PK is gid integer,
> guid uuid, cat text, name text, target integer.
>
> Doing a EXPLAIN ANALYZE DELETE WHERE gid IN (SELECT DISTINCT gid FROM
> temptable) where there is one row in the temptable, I get this:
>
> Delete on play_statistics (cost=1984.14..8037586.36 rows=3734075 width=34)
> (actual time=407093.859..407093.859 rows=0 loops=1)
> -> Hash Join (cost=1984.14..8037586.36 rows=3734075 width=34) (actual
> time=407093.857..407093.857 rows=0 loops=1)
> Hash Cond: (play_statistics.gid = "ANY_subquery".gid)
> -> Seq Scan on play_statistics (cost=0.00..7781818.16 rows=96600516
> width=10) (actual time=201.521..396052.101 rows=96556116 loops=1)
> -> Hash (cost=1981.64..1981.64 rows=200 width=32) (actual
> time=13.020..13.020 rows=1 loops=1)
> Buckets: 1024 Batches: 1 Memory Usage: 9kB
> -> Subquery Scan on "ANY_subquery" (cost=1977.64..1981.64 rows=200
> width=32) (actual time=13.012..13.013 rows=1 loops=1)
> -> HashAggregate (cost=1977.64..1979.64 rows=200 width=4) (actual
> time=13.001..13.002 rows=1 loops=1)
> Group Key: stats.gid
> -> Seq Scan on stats (cost=0.00..1924.91 rows=21091 width=4) (actual
> time=0.028..9.244 rows=21091 loops=1)
> Planning Time: 0.657 ms
> JIT:
> Functions: 15
> Options: Inlining true, Optimization true, Expressions true, Deforming true
> Timing: Generation 1.816 ms, Inlining 53.472 ms, Optimization 89.014 ms,
> Emission 58.759 ms, Total 203.060 ms
> Execution Time: 407112.908 ms
> (16 rows)
>
> It takes 7 minutes to delete 21063 rows for one given gid value, which
> seems excessive given I think it should be using the PK index.
>
> Anything I'm missing here?
>
>
Your command text is over "temptable", but your plan is over "stats". Is
"temptable" a view?

Cheers,

Jeff