本篇内容主要讲解“怎么使用PostgreSQL的pg_stat_statements”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“怎么使用PostgreSQL的pg_stat_statements”吧!

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pg_stat_statements提供了一种跟踪所有SQL语句的手段。

进入pg_stat_statements目录,执行make/make install

[pg12@localhost pg_stat_statements]$ ls
expected                          pg_stat_statements--1.4--1.5.sql  pg_stat_statements.control
Makefile                          pg_stat_statements--1.4.sql       pg_stat_statements.o
pg_stat_statements--1.0--1.1.sql  pg_stat_statements--1.5--1.6.sql  pg_stat_statements.so
pg_stat_statements--1.1--1.2.sql  pg_stat_statements--1.6--1.7.sql  pg_stat_statements--unpackaged--1.0.sql
pg_stat_statements--1.2--1.3.sql  pg_stat_statements.c              sql
pg_stat_statements--1.3--1.4.sql  pg_stat_statements.conf
[pg12@localhost pg_stat_statements]$ make
make -C ../../src/backend generated-headers
make[1]: Entering directory `/data/source/postgresql-12beta1/src/backend'
make -C catalog distprep generated-header-symlinks
make[2]: Entering directory `/data/source/postgresql-12beta1/src/backend/catalog'
make[2]: Nothing to be done for `distprep'.
make[2]: Nothing to be done for `generated-header-symlinks'.
make[2]: Leaving directory `/data/source/postgresql-12beta1/src/backend/catalog'
make -C utils distprep generated-header-symlinks
make[2]: Entering directory `/data/source/postgresql-12beta1/src/backend/utils'
make[2]: Nothing to be done for `distprep'.
make[2]: Nothing to be done for `generated-header-symlinks'.
make[2]: Leaving directory `/data/source/postgresql-12beta1/src/backend/utils'
make[1]: Leaving directory `/data/source/postgresql-12beta1/src/backend'
[pg12@localhost pg_stat_statements]$ make install
make -C ../../src/backend generated-headers
make[1]: Entering directory `/data/source/postgresql-12beta1/src/backend'
make -C catalog distprep generated-header-symlinks
make[2]: Entering directory `/data/source/postgresql-12beta1/src/backend/catalog'
make[2]: Nothing to be done for `distprep'.
make[2]: Nothing to be done for `generated-header-symlinks'.
make[2]: Leaving directory `/data/source/postgresql-12beta1/src/backend/catalog'
make -C utils distprep generated-header-symlinks
make[2]: Entering directory `/data/source/postgresql-12beta1/src/backend/utils'
make[2]: Nothing to be done for `distprep'.
make[2]: Nothing to be done for `generated-header-symlinks'.
make[2]: Leaving directory `/data/source/postgresql-12beta1/src/backend/utils'
make[1]: Leaving directory `/data/source/postgresql-12beta1/src/backend'
/usr/bin/mkdir -p '/appdb/xdb/pg12beta1/lib/postgresql'
/usr/bin/mkdir -p '/appdb/xdb/pg12beta1/share/postgresql/extension'
/usr/bin/mkdir -p '/appdb/xdb/pg12beta1/share/postgresql/extension'
/usr/bin/install -c -m 755  pg_stat_statements.so '/appdb/xdb/pg12beta1/lib/postgresql/pg_stat_statements.so'
/usr/bin/install -c -m 644 ./pg_stat_statements.control '/appdb/xdb/pg12beta1/share/postgresql/extension/'
/usr/bin/install -c -m 644 ./pg_stat_statements--1.4.sql ./pg_stat_statements--1.6--1.7.sql ./pg_stat_statements--1.5--1.6.sql ./pg_stat_statements--1.4--1.5.sql ./pg_stat_statements--1.3--1.4.sql ./pg_stat_statements--1.2--1.3.sql ./pg_stat_statements--1.1--1.2.sql ./pg_stat_statements--1.0--1.1.sql ./pg_stat_statements--unpackaged--1.0.sql  '/appdb/xdb/pg12beta1/share/postgresql/extension/'
[pg12@localhost pg_stat_statements]$

使用前需在配置文件中添加预加载共享链接库,否则会报错:

testdb=# create extension pg_stat_statements;
CREATE EXTENSION
testdb=# select * from pg_stat_statements;
psql: ERROR:  pg_stat_statements must be loaded via shared_preload_libraries

在postgresql.conf文件中修改shared_preload_libraries参数:

[pg12@localhost pg12db1]$ grep 'shared_preload' postgresql.conf 
shared_preload_libraries = 'pg_stat_statements'    # (change requires restart)

注意:修改该参数后需要重启数据库实例.

下面是简单的使用:

testdb=# \x
Expanded display is on.
testdb=# select * from pg_stat_statements;
-[ RECORD 1 ]-------+---------------------------------
userid              | 10
dbid                | 16384
queryid             | 6343734953611294604
query               | select * from pg_stat_statements
calls               | 2
total_time          | 0.618297
min_time            | 0.303231
max_time            | 0.315066
mean_time           | 0.3091485
stddev_time         | 0.00591750000000002
rows                | 2
shared_blks_hit     | 0
shared_blks_read    | 0
shared_blks_dirtied | 0
shared_blks_written | 0
local_blks_hit      | 0
local_blks_read     | 0
local_blks_dirtied  | 0
local_blks_written  | 0
temp_blks_read      | 0
temp_blks_written   | 0
blk_read_time       | 0
blk_write_time      | 0
-[ RECORD 2 ]-------+---------------------------------
userid              | 10
dbid                | 16384
queryid             | -2568307067200732111
query               | select * from t1
calls               | 1
total_time          | 876.219199
min_time            | 876.219199
max_time            | 876.219199
mean_time           | 876.219199
stddev_time         | 0
rows                | 1100000
shared_blks_hit     | 0
shared_blks_read    | 5946
shared_blks_dirtied | 0
shared_blks_written | 0
local_blks_hit      | 0
local_blks_read     | 0
local_blks_dirtied  | 0
local_blks_written  | 0
temp_blks_read      | 0
temp_blks_written   | 0
blk_read_time       | 0
blk_write_time      | 0

查询汇总统计信息

testdb=# SELECT query, 
  (total_time / 1000 / 60) as total, 
  (total_time/calls) as avg
FROM pg_stat_statements 
ORDER BY 1 DESC 
LIMIT 100;
                query                |         total          |         avg         
-------------------------------------+------------------------+---------------------
 SELECT                             +| 1.5928199999999998e-05 |            0.318564
   (total_time / $1 / $2) as total, +|                        | 
   (total_time/calls) as avg,       +|                        | 
   query                            +|                        | 
 FROM pg_stat_statements            +|                        | 
 ORDER BY 1 DESC                    +|                        | 
 LIMIT $3                            |                        | 
 SELECT                             +| 4.9146500000000005e-06 |            0.294879
   (total_time / $1 / $2) as total, +|                        | 
   (total_time/calls) as avg        +|                        | 
 FROM pg_stat_statements            +|                        | 
 ORDER BY 1 DESC                    +|                        | 
 LIMIT $3                            |                        | 
 select * from t1                    |   0.014603653316666666 |          876.219199
 select * from pg_stat_statements    | 1.5696116666666667e-05 | 0.31392233333333336
(4 rows)
...
testdb=# 
testdb=# SELECT 
testdb-#   query, 
testdb-#   round((total_time / 1000 / 60)::numeric,4) as total, 
testdb-#   round((total_time/calls)::numeric,4) as avg
testdb-# FROM pg_stat_statements 
testdb-# WHERE query like '%t1%'
testdb-# ORDER BY 1 DESC 
testdb-# LIMIT 100;
             query              | total  |   avg    
--------------------------------+--------+----------
 select * from t1 where id = $1 | 0.0022 | 129.9684
 select * from t1 where id < $1 | 0.0020 | 121.3334
 select * from t1               | 0.0146 | 876.2192
(3 rows)

查询条件中id = xx,实际值被替换为占位符($x).

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