Re: Select in subselect vs select = any array

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(at)gmail(dot)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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