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 .... ])
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 <atistler@xxxxxxxxx>:
>> 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 <atistler@xxxxxxxxx>:
>>>> 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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