Hola Diego
Gracias por la respuesta, pero.. y qué ventaja tendria? pues lo mismo se
logra con un índice compuesto e incluso este último permitirá filtrar
además por el otro campo, e incluso el optimizador prefirió el índice
compuesto.
El mar., 23 de jun. de 2020 a la(s) 10:41, Diego (mrstephenam...@gmail.com)
escribió:
> HOla, Hellmuth / lista
>
> Lo que pasa es que lo que esta en el include, no se indexa.
>
> Es la forma de no salir del indice para buscar ese valor en particular,
> ahorrando el pase por la tabla
>
> Salu2
> On 2020-06-23 12:03, Hellmuth Vargas wrote:
>
> *Hola Lista*
>
> *Ya que en las últimas versiones de PostgreSQL contamos con
> muchas más herramientas para la optimización de las consultas
> (estadísticas, paralelismo, JIT, etc, etc,etc ) pues hoy me dio por
> probar la cláusula INCLUDE en los índices, con el fin de indagar por su
> correcto uso y/o beneficios, hice este pequeño laboratorio:*
>
> drop table test
>
> create table test(mes text,cantidad int);
>
> insert into test(mes,cantidad)
> select b.mes, trunc(1000000*random())
> FROM generate_series(1,300000) as a
> cross join
> (values('ENE'),('FEB'),('MAR'),('ABR'),('MAY'),('JUN'),('JUL'),('AGO'),('SEP'),('OCT'),('NOV'),('DIC'))
> as b(mes);
>
> analyze test;
>
> *-- sin indices*
> explain (ANALYZE,BUFFERS,TIMING) select sum(cantidad)
> from test where mes='JUN';
>
> ---
> Finalize Aggregate (cost=23742.83..23742.83 rows=1 width=8) (actual
> time=174.405..174.406 rows=1 loops=1)
> Buffers: shared read=15930
> -> Gather (cost=23742.62..23742.83 rows=2 width=8) (actual
> time=174.299..178.505 rows=3 loops=1)
> Workers Planned: 2
> Workers Launched: 2
> Buffers: shared read=15930
> -> Partial Aggregate (cost=22742.62..22742.63 rows=1 width=8)
> (actual time=168.675..168.676 rows=1 loops=3)
> Buffers: shared read=15930
> -> Parallel Seq Scan on test (cost=0.00..22680.00
> rows=125250 width=4) (actual time=0.044..160.487 rows=100000 loops=3)
> Filter: (mes = 'JUN'::text)
> Rows Removed by Filter: 1100000
> Buffers: shared read=15930
> Planning Time: 0.149 ms
> Execution Time: 178.545 ms
>
>
> *-- indice solo por mes*
> create index concurrently idx_test_mes on test(mes);
>
> explain (ANALYZE,BUFFERS,TIMING) select sum(cantidad)
> from test where mes='JUN';
>
>
> Aggregate (cost=18830.72..18830.73 rows=1 width=8) (actual
> time=238.116..238.116 rows=1 loops=1)
> Buffers: shared read=16752
> -> Bitmap Heap Scan on test (cost=1385.12..18679.16 rows=303120
> width=4) (actual time=28.007..206.884 rows=300000 loops=1)
> Recheck Cond: (mes = 'JUN'::text)
> Heap Blocks: exact=15930
> Buffers: shared read=16752
> -> Bitmap Index Scan on idx_test_mes (cost=0.00..1369.97
> rows=303120 width=0) (actual time=25.312..25.312 rows=300000 loops=1)
> Index Cond: (mes = 'JUN'::text)
> Buffers: shared read=822
> Planning Time: 0.321 ms
> Execution Time: 238.150 ms
>
>
> *-- indice por mes incluye cantidad*
> create index concurrently idx_test_mes2 on test(mes) include (cantidad);
>
>
> explain (ANALYZE,BUFFERS,TIMING) select sum(cantidad)
> from test where mes='JUN';
>
> Aggregate (cost=18830.72..18830.73 rows=1 width=8) (actual
> time=227.678..227.678 rows=1 loops=1)
> Buffers: shared read=16752
> -> Bitmap Heap Scan on test (cost=1385.12..18679.16 rows=303120
> width=4) (actual time=26.342..198.513 rows=300000 loops=1)
> Recheck Cond: (mes = 'JUN'::text)
> Heap Blocks: exact=15930
> Buffers: shared read=16752
> -> Bitmap Index Scan on idx_test_mes2 (cost=0.00..1369.97
> rows=303120 width=0) (actual time=23.680..23.680 rows=300000 loops=1)
> Index Cond: (mes = 'JUN'::text)
> Buffers: shared read=822
> Planning Time: 0.540 ms
> Execution Time: 227.710 ms
>
> *-- consulta filtrando mes y cantidad*
> explain (ANALYZE,BUFFERS,TIMING) select sum(cantidad)
> from test where mes='JUN' and cantidad between 1000 and 40000
>
> Aggregate (cost=18973.69..18973.69 rows=1 width=8) (actual
> time=352.304..352.304 rows=1 loops=1)
> Buffers: shared read=16752
> -> Bitmap Heap Scan on test (cost=1370.56..18967.72 rows=11932
> width=4) (actual time=29.374..350.099 rows=11687 loops=1)
> Recheck Cond: (mes = 'JUN'::text)
> Filter: ((cantidad >= 1000) AND (cantidad <= 40000))
> Rows Removed by Filter: 288313
> Heap Blocks: exact=15930
> Buffers: shared read=16752
> -> Bitmap Index Scan on idx_test_mes2 (cost=0.00..1369.97
> rows=303120 width=0) (actual time=26.412..26.412 rows=300000 loops=1)
> Index Cond: (mes = 'JUN'::text)
> Buffers: shared read=822
> Planning Time: 0.684 ms
> Execution Time: 352.349 ms
>
> *-- indice compuesto por mes y cantidad*
> create index concurrently idx_test_mes3 on test(mes,cantidad);
>
> explain (ANALYZE,BUFFERS,TIMING) select sum(cantidad)
> from test where mes='JUN';
>
>
> Aggregate (cost=18830.72..18830.73 rows=1 width=8) (actual
> time=234.626..234.627 rows=1 loops=1)
> Buffers: shared read=16752
> -> Bitmap Heap Scan on test (cost=1385.12..18679.16 rows=303120
> width=4) (actual time=31.220..203.525 rows=300000 loops=1)
> Recheck Cond: (mes = 'JUN'::text)
> Heap Blocks: exact=15930
> Buffers: shared read=16752
> -> Bitmap Index Scan on idx_test_mes3 (cost=0.00..1369.97
> rows=303120 width=0) (actual time=28.165..28.165 rows=300000 loops=1)
> Index Cond: (mes = 'JUN'::text)
> Buffers: shared read=822
> Planning Time: 0.191 ms
> Execution Time: 234.656 ms
>
>
> * -- consulta filtrando mes y cantidad *
> explain (ANALYZE,BUFFERS,TIMING) select sum(cantidad)
> from test where mes='JUN' and cantidad between 1000 and 40000
>
> Aggregate (cost=9046.67..9046.67 rows=1 width=8) (actual
> time=174.658..174.659 rows=1 loops=1)
> Buffers: shared read=8403
> -> Bitmap Heap Scan on test (cost=66.81..9040.70 rows=11932 width=4)
> (actual time=6.184..171.275 rows=11687 loops=1)
> Recheck Cond: ((mes = 'JUN'::text) AND (cantidad >= 1000) AND
> (cantidad <= 40000))
> Heap Blocks: exact=8368
> Buffers: shared read=8403
> -> Bitmap Index Scan on idx_test_mes3 (cost=0.00..66.22
> rows=11932 width=0) (actual time=4.535..4.535 rows=11687 loops=1)
> Index Cond: ((mes = 'JUN'::text) AND (cantidad >= 1000) AND
> (cantidad <= 40000))
> Buffers: shared read=35
> Planning Time: 0.732 ms
> Execution Time: 174.706 ms
>
>
>
> *-- tamaños de la tabla e indices creados*
> SELECT
>
>
> nspname,relname,pg_relation_size(c.oid),pg_size_pretty(pg_relation_size(c.oid))
> as "size"
> from pg_class c left join pg_namespace n on ( n.oid=c.relnamespace)
> where nspname not in ('pg_catalog','information_schema') and relname ilike
> '%test%'
> order by pg_relation_size(c.oid) desc;
>
> nspname;relname; pg_relation_size;size
> public;test;130498560;124 MB
> public;idx_test_mes;80887808;77 MB
> public;idx_test_mes2;80887808;77 MB
> public;idx_test_mes3;80887808;77 MB
>
> *La pregunta es, en qué situaciones se debe emplear o se justifica un
> include versus, por ejemplo, un índice compuesto? de antemano gracias*
>
> --
> Cordialmente,
>
> Ing. Hellmuth I. Vargas S.
>
>
--
Cordialmente,
Ing. Hellmuth I. Vargas S.
Esp. Telemática y Negocios por Internet
Oracle Database 10g Administrator Certified Associate
EnterpriseDB Certified PostgreSQL 9.3 Associate
