Обсуждение: [PERFORM] slow index scan performance
Consider these 2 index scan produced by a query
--
Soni Maula Harriz
-> 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 ?
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,
It's Postgres 9.1.24 on RHEL 6.5
On Tue, Sep 5, 2017 at 8:24 PM, Soni M <diptatapa@gmail.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_idIndex Cond: (rl2.activity_id = rl.activity_id)Filter: rl2.successBuffers: 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_idIndex Cond: (a.activity_id = rl.activity_id)Buffers: shared hit=137925 read=32728And it's sizeconscopy=# 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,
Trying on another server, it gives different result.
-> Index Scan using response_log_by_activity on public.response_log rl2 (cost=0.00..50.29 rows=17 width=8) (actual time=0.955..0.967 rows=0 loops=30895)
Output: rl2.activity_id, rl2.feed_id
Index Cond: (rl2.activity_id = rl.activity_id)
Filter: rl2.success
Buffers: shared hit=2311312 read=132342
-> Index Scan using activity_pkey on public.activity a (cost=0.00..49.79 rows=1 width=12) (actual time=13.747..13.762 rows=1 loops=30892)
Output: a.status_id, a.activity_id, a.visit_id
Index Cond: (a.activity_id = rl.activity_id)
Buffers: shared hit=124463 read=30175
Now, index scan on activity_pkey which take much slower. Can someone please explain these ?
Thanks
On Tue, Sep 5, 2017 at 8:46 PM, Soni M <diptatapa@gmail.com> wrote:
It's Postgres 9.1.24 on RHEL 6.5On Tue, Sep 5, 2017 at 8:24 PM, Soni M <diptatapa@gmail.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_idIndex Cond: (rl2.activity_id = rl.activity_id)Filter: rl2.successBuffers: 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_idIndex Cond: (a.activity_id = rl.activity_id)Buffers: shared hit=137925 read=32728And it's sizeconscopy=# 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
Regards,