mydbab=# \d+ table1;
Table "dbmydb.table1"
Column | Type | Modifiers | Scol5rage | Stats target | Description
----------------+---------+-----------+------------+--------------+-------------
pk | bigint | not null | plain | |
col1 | bigint | not null | plain | |
col2 | citext | not null | extended | |
col3 | citext | | extended | |
col4 | citext | not null | extended | |
col5 | citext | | extended | |
col6 | citext | | extended | |
bcol7 | citext | | extended | |
col8 | citext | | extended | |
col9 | citext | | extended | |
col10 | bigint | not null | plain | |
col11 | citext | | extended | |
col12 | bigint | | plain | |
col13 | integer | default 1 | plain | |
col14 | integer | default 0 | plain | |
col15 | bigint | | plain | |
col16 | integer | default 0 | plain | |
col17 | integer | default 0 | plain | |
col18 | integer | default 0 | plain | |
col19 | citext | | extended | |
col20 | citext | | extended | |
col21 | citext | | extended | |
索引：
"table1_pk" PRIMARY KEY, btree (pk)
"table1_idx3" btree (col10)
"table1_idx4" btree ("col4")
"table1_idx5" btree (col11)
"table1_idx6" btree (col15)
"table1_fk_idx" btree (col1)
检查约束：
"table1_col6_c" CHECK (length(col6::text) <= 5000)
"table1_col4_c" CHECK (length("col4"::text) <= 253)
"table1_col5_c” CHECK (length(col5::text) <= 5000)
"table1_col3_c" CHECK (length(col3::text) <= 253)
"table1_col11_c" CHECK (length(col11::text) <= 253)
"table1_col20_c” CHECK (length(col20::text) <= 200)
"table1_col21_c” CHECK (length(col21::text) <= 500)
"table1_col7_c” CHECK (length(col7::text) <= 500)
"table1_col9_c" CHECK (length(col9::text) <= 100)
"table1_col5_c" CHECK (length("col5"::text) <= 5000)
"table1_col19_c” CHECK (length(col19::text) <= 100)
外键约束：
"table1_fk" FOREIGN KEY (col1) REFERENCES table2(col1) ON DELETE CASCADE
参考：
TABLE “table3” CONSTRAINT “table3_fk2" FOREIGN KEY (pk) REFERENCES table1(pk) ON DELETE CASCADE
TABLE “table4” CONSTRAINT “table4_fk2" FOREIGN KEY (pk) REFERENCES table1(pk) ON DELETE CASCADE
TABLE “table5” CONSTRAINT “table5_fk1" FOREIGN KEY (pk) REFERENCES table1(pk)
TABLE “table6” CONSTRAINT “table6_fk" FOREIGN KEY (pk) REFERENCES table1(pk) ON DELETE CASCADE
TABLE “table7” CONSTRAINT “table7_fk1" FOREIGN KEY (pk) REFERENCES table1(pk) ON DELETE CASCADE
选项：autovacuum_vacuum_scale_factor=0.05
查询计划
explain SELECT * FROM table1 WHERE ((table1.col1 = 814000000002054) AND (((table1.pk >= 238000000000000) AND (table1.pk <= 238999999999999)) OR ((table1.pk >= 0) AND (table1.pk <= 999999999999)))) ORDER BY table1.col15 DESC LIMIT 7
(query gets timed out for explain analyze)
Limit (cost=0.56..607.64 rows=7 width=603)
Index Scan Backward using table1_idx6 on table1 (cost=0.56..12622561.13 rows=145548 width=603) Filter: ((col1 = 814000000002054::bigint) AND (((pk >= 238000000000000::bigint) AND (pk <= 238999999999999::bigint)) OR ((pk >= 0) AND (pk <= 999999999999::bigint))))
问题： 表有50M的记录。 此查询运行时间超过15分钟！我们已经校准到自动真空到0.05。自动分析是PG的默认值。 查询甚至更改为ORDER BY table1.col15 ASC LIMIT 7，即使查询大约在同一时间。 插入/更新操作只需ms。
历史：当数据较少时，结果会更快 - 查询在MySQL中没有问题，几周前就迁移到了Pg。
Worker_mem是956MB。
select version();
PostgreSQL 9.4.0 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-54), 64-bit
(1 row)
答案 0 :(得分：0)
尝试创建多列索引：
CREATE INDEX ON table1(col15, col1, pk);