好的,我在一个更接近我的用例的表格上运行了这个操作。要么我做错了,要么crosstab不适合我的情况。
首先,我创建了一些类似的数据:
CREATE TABLE public.test (
id serial primary key,
msrmnt integer,
entity integer,
localt timestamp,
val double precision
);
CREATE INDEX ix_test_msrmnt
ON public.test (msrmnt);
CREATE INDEX ix_public_test_201201_entity
ON public.test (entity);
CREATE INDEX ix_public_test_201201_localt
ON public.test (localt);
insert into public.test (msrmnt, entity, localt, val)
select *
from(
SELECT msrmnt, entity, localt, random() as val
FROM generate_series('2012-01-01'::timestamp, '2012-01-01 23:59:00'::timestamp, interval '1 minutes') as localt
join
(select *
FROM generate_series(1, 50, 1) as msrmnt) as msrmnt
on 1=1
join
(select *
FROM generate_series(1, 200, 1) as entity) as entity
on 1=1) as data;
然后我运行了交叉表代码几次:
explain analyze
SELECT (timestamp 'epoch' + row_name[1] * INTERVAL '1 second')::date As localt, row_name[2] as entity
,msrmnt01,msrmnt02,msrmnt03,msrmnt04,msrmnt05,msrmnt06,msrmnt07,msrmnt08,msrmnt09,msrmnt10
,msrmnt11,msrmnt12,msrmnt13,msrmnt14,msrmnt15,msrmnt16,msrmnt17,msrmnt18,msrmnt19,msrmnt20
,msrmnt21,msrmnt22,msrmnt23,msrmnt24,msrmnt25,msrmnt26,msrmnt27,msrmnt28,msrmnt29,msrmnt30
,msrmnt31,msrmnt32,msrmnt33,msrmnt34,msrmnt35,msrmnt36,msrmnt37,msrmnt38,msrmnt39,msrmnt40
,msrmnt41,msrmnt42,msrmnt43,msrmnt44,msrmnt45,msrmnt46,msrmnt47,msrmnt48,msrmnt49,msrmnt50
FROM crosstab('SELECT ARRAY[extract(epoch from localt), entity] as row_name, msrmnt, val
FROM public.test
ORDER BY localt, entity, msrmnt',$$VALUES ( 1::text),( 2::text),( 3::text),( 4::text),( 5::text),( 6::text),( 7::text),( 8::text),( 9::text),(10::text)
,(11::text),(12::text),(13::text),(14::text),(15::text),(16::text),(17::text),(18::text),(19::text),(20::text)
,(21::text),(22::text),(23::text),(24::text),(25::text),(26::text),(27::text),(28::text),(29::text),(30::text)
,(31::text),(32::text),(33::text),(34::text),(35::text),(36::text),(37::text),(38::text),(39::text),(40::text)
,(41::text),(42::text),(43::text),(44::text),(45::text),(46::text),(47::text),(48::text),(49::text),(50::text)$$)
as ct (row_name integer[],msrmnt01 double precision, msrmnt02 double precision,msrmnt03 double precision, msrmnt04 double precision,msrmnt05 double precision,
msrmnt06 double precision,msrmnt07 double precision, msrmnt08 double precision,msrmnt09 double precision, msrmnt10 double precision
,msrmnt11 double precision, msrmnt12 double precision,msrmnt13 double precision, msrmnt14 double precision,msrmnt15 double precision,
msrmnt16 double precision,msrmnt17 double precision, msrmnt18 double precision,msrmnt19 double precision, msrmnt20 double precision
,msrmnt21 double precision, msrmnt22 double precision,msrmnt23 double precision, msrmnt24 double precision,msrmnt25 double precision,
msrmnt26 double precision,msrmnt27 double precision, msrmnt28 double precision,msrmnt29 double precision, msrmnt30 double precision
,msrmnt31 double precision, msrmnt32 double precision,msrmnt33 double precision, msrmnt34 double precision,msrmnt35 double precision,
msrmnt36 double precision,msrmnt37 double precision, msrmnt38 double precision,msrmnt39 double precision, msrmnt40 double precision
,msrmnt41 double precision, msrmnt42 double precision,msrmnt43 double precision, msrmnt44 double precision,msrmnt45 double precision,
msrmnt46 double precision,msrmnt47 double precision, msrmnt48 double precision,msrmnt49 double precision, msrmnt50 double precision)
limit 1000
第三次尝试获得这个结果:
QUERY PLAN
Limit (cost=0.00..20.00 rows=1000 width=432) (actual time=110236.673..110237.667 rows=1000 loops=1)
-> Function Scan on crosstab ct (cost=0.00..20.00 rows=1000 width=432) (actual time=110236.672..110237.598 rows=1000 loops=1)
Total runtime: 110699.598 ms
然后我运行了标准解决方案几次:
explain analyze
select localt, entity,
max(case when msrmnt = 1 then val else null end) as msrmnt01
,max(case when msrmnt = 2 then val else null end) as msrmnt02
,max(case when msrmnt = 3 then val else null end) as msrmnt03
,max(case when msrmnt = 4 then val else null end) as msrmnt04
,max(case when msrmnt = 5 then val else null end) as msrmnt05
,max(case when msrmnt = 6 then val else null end) as msrmnt06
,max(case when msrmnt = 7 then val else null end) as msrmnt07
,max(case when msrmnt = 8 then val else null end) as msrmnt08
,max(case when msrmnt = 9 then val else null end) as msrmnt09
,max(case when msrmnt = 10 then val else null end) as msrmnt10
,max(case when msrmnt = 11 then val else null end) as msrmnt11
,max(case when msrmnt = 12 then val else null end) as msrmnt12
,max(case when msrmnt = 13 then val else null end) as msrmnt13
,max(case when msrmnt = 14 then val else null end) as msrmnt14
,max(case when msrmnt = 15 then val else null end) as msrmnt15
,max(case when msrmnt = 16 then val else null end) as msrmnt16
,max(case when msrmnt = 17 then val else null end) as msrmnt17
,max(case when msrmnt = 18 then val else null end) as msrmnt18
,max(case when msrmnt = 19 then val else null end) as msrmnt19
,max(case when msrmnt = 20 then val else null end) as msrmnt20
,max(case when msrmnt = 21 then val else null end) as msrmnt21
,max(case when msrmnt = 22 then val else null end) as msrmnt22
,max(case when msrmnt = 23 then val else null end) as msrmnt23
,max(case when msrmnt = 24 then val else null end) as msrmnt24
,max(case when msrmnt = 25 then val else null end) as msrmnt25
,max(case when msrmnt = 26 then val else null end) as msrmnt26
,max(case when msrmnt = 27 then val else null end) as msrmnt27
,max(case when msrmnt = 28 then val else null end) as msrmnt28
,max(case when msrmnt = 29 then val else null end) as msrmnt29
,max(case when msrmnt = 30 then val else null end) as msrmnt30
,max(case when msrmnt = 31 then val else null end) as msrmnt31
,max(case when msrmnt = 32 then val else null end) as msrmnt32
,max(case when msrmnt = 33 then val else null end) as msrmnt33
,max(case when msrmnt = 34 then val else null end) as msrmnt34
,max(case when msrmnt = 35 then val else null end) as msrmnt35
,max(case when msrmnt = 36 then val else null end) as msrmnt36
,max(case when msrmnt = 37 then val else null end) as msrmnt37
,max(case when msrmnt = 38 then val else null end) as msrmnt38
,max(case when msrmnt = 39 then val else null end) as msrmnt39
,max(case when msrmnt = 40 then val else null end) as msrmnt40
,max(case when msrmnt = 41 then val else null end) as msrmnt41
,max(case when msrmnt = 42 then val else null end) as msrmnt42
,max(case when msrmnt = 43 then val else null end) as msrmnt43
,max(case when msrmnt = 44 then val else null end) as msrmnt44
,max(case when msrmnt = 45 then val else null end) as msrmnt45
,max(case when msrmnt = 46 then val else null end) as msrmnt46
,max(case when msrmnt = 47 then val else null end) as msrmnt47
,max(case when msrmnt = 48 then val else null end) as msrmnt48
,max(case when msrmnt = 49 then val else null end) as msrmnt49
,max(case when msrmnt = 50 then val else null end) as msrmnt50
from sample
group by localt, entity
limit 1000
第三次尝试获得此结果:
QUERY PLAN
Limit (cost=2257339.69..2270224.77 rows=1000 width=24) (actual time=19795.984..20090.626 rows=1000 loops=1)
-> GroupAggregate (cost=2257339.69..5968242.35 rows=288000 width=24) (actual time=19795.983..20090.496 rows=1000 loops=1)
-> Sort (cost=2257339.69..2293339.91 rows=14400088 width=24) (actual time=19795.626..19808.820 rows=50001 loops=1)
Sort Key: localt
Sort Method: external merge Disk: 478568kB
-> Seq Scan on sample (cost=0.00..249883.88 rows=14400088 width=24) (actual time=0.013..2245.247 rows=14400000 loops=1)
Total runtime: 20197.565 ms
因此,对于我的情况来说,到目前为止,交叉表似乎不是一个解决方案。而这只是我将有多年的其中一天。实际上,尽管测量哪些实体是可变的并且会引入新的实体,但我可能仍然需要使用宽格式(非规范化)表格,但我不会在这里详细介绍。
以下是我在使用Postgres 9.2.3时的一些设置:
name setting
max_connections 100
shared_buffers 2097152
effective_cache_size 6291456
maintenance_work_mem 1048576
work_mem 262144