2011/3/21 Adam Tistler <atist...@gmail.com>:
> Pavel, thanks for the help.
>
> I increased work_mem from 16MB to 64MB, no difference. The queries are
> really just a test case. My actual queries are actual just large number of
> primary keys that I am selecting from the db:
>
> For example:
> select * from nodes where node_id in ( 1, 2, 3 ..... )
>
> I found that even for small queries, the following is faster:
> select * from nodes where node_in = any (array[1,2,3 .... ])
it depends on version. I think so on last postgres, these queries are
same, not sure.
Regards
Pavel
>
>
> Its not really a big deal to me, I was just wondering if others could
> reproduce it on other systems/versions and if perhaps this is an issue that I
> should point out to postgres-dev.
>
>
> Results below:
>
> logicops2=# explain analyze select count(*) from nodes where node_id in (
> select node_id from nodes limit 100000 );
> QUERY PLAN
> ----------------------------------------------------------------------------------------------------------------------------------------
> Aggregate (cost=3017.18..3017.19 rows=1 width=0) (actual
> time=1017.051..1017.051 rows=1 loops=1)
> -> Nested Loop (cost=2887.05..3016.68 rows=200 width=0) (actual
> time=157.290..986.329 rows=100000 loops=1)
> -> HashAggregate (cost=2887.05..2889.05 rows=200 width=4) (actual
> time=157.252..241.995 rows=100000 loops=1)
> -> Limit (cost=0.00..1637.05 rows=100000 width=4) (actual
> time=0.009..73.942 rows=100000 loops=1)
> -> Seq Scan on nodes (cost=0.00..12355.34 rows=754734
> width=4) (actual time=0.008..35.428 rows=100000 loops=1)
> -> Index Scan using n_node_id_index on nodes (cost=0.00..0.63
> rows=1 width=4) (actual time=0.006..0.006 rows=1 loops=100000)
> Index Cond: (public.nodes.node_id = public.nodes.node_id)
> Total runtime: 1017.794 ms
> (8 rows)
>
> logicops2=# explain analyze select count(*) from nodes where node_id =
> any(array ( select node_id from nodes limit 100000 ));
> QUERY PLAN
> -----------------------------------------------------------------------------------------------------------------------------------------
> Aggregate (cost=1718.60..1718.61 rows=1 width=0) (actual
> time=485.554..485.555 rows=1 loops=1)
> InitPlan 1 (returns $0)
> -> Limit (cost=0.00..1637.05 rows=100000 width=4) (actual
> time=0.011..73.037 rows=100000 loops=1)
> -> Seq Scan on nodes (cost=0.00..12355.34 rows=754734 width=4)
> (actual time=0.010..34.462 rows=100000 loops=1)
> -> Bitmap Heap Scan on nodes (cost=42.67..81.53 rows=10 width=0) (actual
> time=433.003..461.108 rows=100000 loops=1)
> Recheck Cond: (node_id = ANY ($0))
> -> Bitmap Index Scan on n_node_id_index (cost=0.00..42.67 rows=10
> width=0) (actual time=432.810..432.810 rows=100000 loops=1)
> Index Cond: (node_id = ANY ($0))
> Total runtime: 485.638 ms
> (9 rows)
>
> On Mar 21, 2011, at 1:54 AM, Pavel Stehule wrote:
>
>> Hello
>>
>> I think so HashAggregate goes out of memory - you can try to increase
>> a work_mem.
>>
>> There are better queries for counting duplicit then cross join
>>
>> Regards
>>
>> Pavel Stehule
>>
>> 2011/3/21 Adam Tistler <atist...@gmail.com>:
>>> logicops2=# explain analyze select count(*) from nodes where node_id = any(
>>> Array(select node_id from nodes limit 100000) );
>>> QUERY PLAN
>>> -----------------------------------------------------------------------------------------------------------------------------------------
>>> Aggregate (cost=1718.59..1718.60 rows=1 width=0) (actual
>>> time=509.126..509.127 rows=1 loops=1)
>>> InitPlan 1 (returns $0)
>>> -> Limit (cost=0.00..1637.04 rows=100000 width=4) (actual
>>> time=0.010..76.604 rows=100000 loops=1)
>>> -> Seq Scan on nodes (cost=0.00..12355.41 rows=754741 width=4)
>>> (actual time=0.008..38.105 rows=100000 loops=1)
>>> -> Bitmap Heap Scan on nodes (cost=42.67..81.53 rows=10 width=0)
>>> (actual time=447.274..484.283 rows=100000 loops=1)
>>> Recheck Cond: (node_id = ANY ($0))
>>> -> Bitmap Index Scan on n_node_id_index (cost=0.00..42.67 rows=10
>>> width=0) (actual time=447.074..447.074 rows=100000 loops=1)
>>> Index Cond: (node_id = ANY ($0))
>>> Total runtime: 509.209 ms
>>> (9 rows)
>>>
>>> Time: 510.009 ms
>>>
>>>
>>> logicops2=# explain analyze select count(*) from nodes where node_id in
>>> (select node_id from nodes limit 100000);
>>> QUERY PLAN
>>> ----------------------------------------------------------------------------------------------------------------------------------------
>>> Aggregate (cost=3017.17..3017.18 rows=1 width=0) (actual
>>> time=1052.866..1052.866 rows=1 loops=1)
>>> -> Nested Loop (cost=2887.04..3016.67 rows=200 width=0) (actual
>>> time=167.310..1021.540 rows=100000 loops=1)
>>> -> HashAggregate (cost=2887.04..2889.04 rows=200 width=4) (actual
>>> time=167.198..251.205 rows=100000 loops=1)
>>> -> Limit (cost=0.00..1637.04 rows=100000 width=4) (actual
>>> time=0.008..80.090 rows=100000 loops=1)
>>> -> Seq Scan on nodes (cost=0.00..12355.41 rows=754741
>>> width=4) (actual time=0.007..41.566 rows=100000 loops=1)
>>> -> Index Scan using n_node_id_index on nodes (cost=0.00..0.63
>>> rows=1 width=4) (actual time=0.006..0.007 rows=1 loops=100000)
>>> Index Cond: (public.nodes.node_id = public.nodes.node_id)
>>> Total runtime: 1053.523 ms
>>> (8 rows)
>>>
>>> Time: 1054.864 ms
>>>
>>>
>>>
>>> On Mar 20, 2011, at 2:51 AM, Pavel Stehule wrote:
>>>
>>>> Hello
>>>>
>>>> 2011/3/20 Adam Tistler <atist...@gmail.com>:
>>>>> I have noticed that SELECT ... = ANY(ARRAY(...)) is about twice as fast
>>>>> as SELECT IN ( ... ).
>>>>> Can anyone explain a reason for this? Results are the bottom and are
>>>>> reproducible. I can test with other versions if that is necessary.
>>>>>
>>>>
>>>> send a result of EXPLAIN ANALYZE SELECT ..., please
>>>>
>>>> The reasons can be different - less seq scans, indexes
>>>>
>>>> Regards
>>>>
>>>> Pavel Stehule
>>>>
>>>>
>>>>
>>>>> ./configure --prefix=/usr/local/pgsql84 --with-openssl --with-perl
>>>>> CentOS release 5.4 (Final)
>>>>> psql (PostgreSQL) 8.4.1
>>>>>
>>>>> prompt2=# select count(*) from nodes;
>>>>> count
>>>>> --------
>>>>> 754734
>>>>> (1 row)
>>>>>
>>>>>
>>>>> prompt2=# \d nodes
>>>>> Table "public.nodes"
>>>>> Column | Type |
>>>>> Modifiers
>>>>> --------------+--------------------------+-----------------------------------------------------------
>>>>> node_id | integer | not null default
>>>>> nextval(('node_id_seq'::text)::regclass)
>>>>> node_type_id | integer | not null
>>>>> template_id | integer | not null
>>>>> timestamp | timestamp with time zone | default
>>>>> ('now'::text)::timestamp(6) with time zone
>>>>> Indexes:
>>>>> "nodes_pkey" PRIMARY KEY, btree (node_id)
>>>>> "n_node_id_index" btree (node_id)
>>>>> "n_node_type_id_index" btree (node_type_id)
>>>>> "n_template_id_index" btree (template_id)
>>>>>
>>>>> prompt2=# select count(*) from nodes where node_id = any( Array(select
>>>>> node_id from nodes limit 100000) );
>>>>> count
>>>>> --------
>>>>> 100000
>>>>> (1 row)
>>>>>
>>>>> Time: 404.530 ms
>>>>> prompt2=# select count(*) from nodes where node_id = any( Array(select
>>>>> node_id from nodes limit 100000) );
>>>>> count
>>>>> --------
>>>>> 100000
>>>>> (1 row)
>>>>>
>>>>> Time: 407.316 ms
>>>>> prompt2=# select count(*) from nodes where node_id = any( Array(select
>>>>> node_id from nodes limit 100000) );
>>>>> count
>>>>> --------
>>>>> 100000
>>>>> (1 row)
>>>>>
>>>>> Time: 408.728 ms
>>>>> prompt2=# select count(*) from nodes where node_id in (select node_id
>>>>> from nodes limit 100000 );
>>>>> count
>>>>> --------
>>>>> 100000
>>>>> (1 row)
>>>>>
>>>>> Time: 793.840 ms
>>>>> prompt2=# select count(*) from nodes where node_id in (select node_id
>>>>> from nodes limit 100000 );
>>>>> count
>>>>> --------
>>>>> 100000
>>>>> (1 row)
>>>>>
>>>>> Time: 779.137 ms
>>>>> prompt2=# select count(*) from nodes where node_id in (select node_id
>>>>> from nodes limit 100000 );
>>>>> count
>>>>> --------
>>>>> 100000
>>>>> (1 row)
>>>>>
>>>>> Time: 781.820 ms
>>>>>
>>>>>
>>>>> --
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>>>
>
>
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