Re: slow index scan performance

It's Postgres 9.1.24 on RHEL 6.5

On Tue, Sep 5, 2017 at 8:24 PM, Soni M <diptatapa(at)gmail(dot)com> wrote:

> Consider these 2 index scan produced by a query
>
> -> Index Scan using response_log_by_activity on public.response_log rl2
> (cost=0.00..51.53 rows=21 width=8) (actual time=9.017..9.056 rows=0
> loops=34098)
> Output: rl2.activity_id, rl2.feed_id
> Index Cond: (rl2.activity_id =
> rl.activity_id)
> Filter: rl2.success
> Buffers: shared hit=3357159
> read=153313
> -> Index Scan using activity_pkey on
> public.activity a (cost=0.00..51.10 rows=1 width=12) (actual
> time=0.126..0.127 rows=1 loops=34088)
> Output: a.status_id, a.activity_id,
> a.visit_id
> Index Cond: (a.activity_id =
> rl.activity_id)
> Buffers: shared hit=137925 read=32728
>
>
> And it's size
>
> conscopy=# select pg_size_pretty(pg_relation_size('response_log_by_
> activity'::regclass));
> pg_size_pretty
> ----------------
> 7345 MB
> (1 row)
>
> conscopy=# select pg_size_pretty(pg_relation_size('activity_pkey'::
> regclass));
> pg_size_pretty
> ----------------
> 8110 MB
> (1 row)
>
> Index scan on response_log_by_activity is far slower. The table has just
> been repacked, and index rebuilt, but still slow.
>
> Is there any other way to make it faster ?
>
> Why Buffers: shared hit=3,357,159 read=153,313 on response_log_by_activity
> is much bigger than Buffers: shared hit=137925 read=32728 on activity_pkey
> while activity_pkey size is bigger ?
>
> --
> Regards,
>
> Soni Maula Harriz
>

--
Regards,

Soni Maula Harriz