问题:
SELECT new_filename
FROM tmp2_import_lightnings_filenames
WHERE new_filename
NOT IN (SELECT filename FROM service.import_lightnings_filenames LIMIT 64500)
LIMIT 1;
执行时间:62 毫秒。
SELECT new_filename
FROM tmp2_import_lightnings_filenames
WHERE new_filename
NOT IN (SELECT filename FROM service.import_lightnings_filenames LIMIT 65000)
LIMIT 1;
执行时间:4.742 秒。
(所有限制仅用于测试)。
巨大的滞后!并且呈指数增长。
表格:
CREATE TABLE public.tmp2_import_lightnings_filenames (
new_filename VARCHAR(63) NOT NULL,
CONSTRAINT tmp2_import_lightnings_filenames_pkey PRIMARY KEY(new_filename)
) WITHOUT OIDS;
表大小:7304 个字符串
数据示例:/xml/2012-07-13/01/01-24.xml
CREATE TABLE service.import_lightnings_filenames (
id SERIAL,
filename VARCHAR(63) NOT NULL,
imported BOOLEAN DEFAULT false,
strokes_num INTEGER,
CONSTRAINT import_lightnings_filenames_pkey PRIMARY KEY(id)
) WITHOUT OIDS;
CREATE UNIQUE INDEX import_lightnings_filenames_idx
ON service.import_lightnings_filenames
USING btree (filename COLLATE pg_catalog."default");
表大小:70812 个字符串
数据示例:44;/xml/2012-05-26/12/12-18.xml;TRUE;NULL
查询计划:
Limit (cost=0.00..2108.11 rows=1 width=29) (actual time=240.183..240.183 rows=1 loops=1)
Buffers: shared hit=539, temp written=307
-> Seq Scan on tmp2_import_lightnings_filenames (cost=0.00..7698823.12 rows=3652 width=29) (actual time=240.181..240.181 rows=1 loops=1)
Filter: (NOT (SubPlan 1))
Buffers: shared hit=539, temp written=307
SubPlan 1
-> Materialize (cost=0.00..1946.82 rows=64500 width=29) (actual time=0.009..198.313 rows=64500 loops=1)
Buffers: shared hit=538, temp written=307
-> Limit (cost=0.00..1183.32 rows=64500 width=29) (actual time=0.005..113.196 rows=64500 loops=1)
Buffers: shared hit=538
-> Seq Scan on import_lightnings_filenames (cost=0.00..1299.12 rows=70812 width=29) (actual time=0.004..42.418 rows=64500 loops=1)
Buffers: shared hit=538
Total runtime: 240.982 ms
Limit (cost=0.00..2125.03 rows=1 width=29) (actual time=30734.619..30734.619 rows=1 loops=1)
Buffers: shared hit=547, temp read=112258 written=669
-> Seq Scan on tmp2_import_lightnings_filenames (cost=0.00..7760626.00 rows=3652 width=29) (actual time=30734.617..30734.617 rows=1 loops=1)
Filter: (NOT (SubPlan 1))
Buffers: shared hit=547, temp read=112258 written=669
SubPlan 1
-> Materialize (cost=0.00..1962.49 rows=65000 width=29) (actual time=0.798..42.306 rows=64820 loops=363)
Buffers: shared hit=543, temp read=112258 written=669
-> Limit (cost=0.00..1192.49 rows=65000 width=29) (actual time=0.005..116.110 rows=65000 loops=1)
Buffers: shared hit=543
-> Seq Scan on import_lightnings_filenames (cost=0.00..1299.12 rows=70812 width=29) (actual time=0.003..43.804 rows=65000 loops=1)
Buffers: shared hit=543
Total runtime: 30735.267 ms
我做错了什么?