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pg_stat_statements模块提供一种方法追踪一个服务器所执行的所有 SQL 语句的执行统计信息。
该模块必须通过在 postgresql.conf 的 shared_preload_libraries 中增加pg_stat_statements 来载入，因为它需要额外的共享内存。这意味着增加或移除该模块需要一次服务器重启。
当 pg_stat_statements 被载入时，它会跟踪该服务器 的所有数据库的统计信息。该模块提供了一个视图 pg_stat_statements 以及函数 pg_stat_statements_reset 和pg_stat_statements 用于访问和操纵这些统计信息。这些视图 和函数不是全局可用的，但是可以用 CREATE EXTENSION pg_stat_statements 为特定数据库启用它们。
apt 、yum 安装
需要安装相同版本的contrib包，以ubuntu为例。
# apt install postgresql-contrib-9.6
# dpkg -l |grep -i postgresql-contrib-9.6
ii postgresql-contrib-9.6 9.6.8-1.pgdg16.04+1 amd64 additional facilities for PostgreSQL
源码编译安装
编译安装时如果是如下方式，则已经安装了。
$ make world
$ make install-world
否则，需要进入到源码的 \contrib\pg_stat_statements\ 下单独编译安装
$ cd /tmp/postgresql-9.6.8\contrib\pg_stat_statements\
$ make
$ make install
创建 pg_stat_statements
由于pg_stat_statements 既使用了hook，同时又是以 extension 形式被使用，所以需要做两件事情：
1、修改 postgrsql.conf 的 shared_preload_libraries 值后，重启postgresql。
$ vi postgresql.conf
shared_preload_libraries = 'pg_stat_statements' # (change requires restart)
# systemctl stop postgresql
# systemctl start postgresql
2、创建 extension
由于pg_stat_statements针对的是数据库级别，所以需要首先进入指定数据库
postgres=# \c peiybdb
peiybdb=# create extension pg_stat_statements；
创建好后，多出一个视图 pg_stat_statements 和 两个函数 pg_stat_statements_reset;
peiybdb=# \df
List of functions
Schema | Name | Result data type | Argument data types | Type
--------+--------------------------+------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------
public | pg_stat_statements | SETOF record | showtext boolean, OUT userid oid, OUT dbid oid, OUT queryid bigint, OUT query text, OUT calls bigint, OUT total_time double precision, OUT min_time double precision, OUT max_time double precision, OUT mean_time double precision, OUT stddev_time double precision, OUT rows bigint, OUT shared_blks_hit bigint, OUT shared_blks_read bigint, OUT shared_blks_dirtied bigint, OUT shared_blks_written bigint, OUT local_blks_hit bigint, OUT local_blks_read bigint, OUT local_blks_dirtied bigint, OUT local_blks_written bigint, OUT temp_blks_read bigint, OUT temp_blks_written bigint, OUT blk_read_time double precision, OUT blk_write_time double precision | normal
public | pg_stat_statements_reset | void | | normal
(2 rows)
peiybdb=# \df+ pg_stat_statements
List of functions
Schema | Name | Result data type | Argument data types | Type | Volatility | Parallel | Owner | Security | Access privileges | Language | Source code | Description
--------+--------------------+------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------+----------+----------+----------+-------------------+----------+------------------------+-------------
public | pg_stat_statements | SETOF record | showtext boolean, OUT userid oid, OUT dbid oid, OUT queryid bigint, OUT query text, OUT calls bigint, OUT total_time double precision, OUT min_time double precision, OUT max_time double precision, OUT mean_time double precision, OUT stddev_time double precision, OUT rows bigint, OUT shared_blks_hit bigint, OUT shared_blks_read bigint, OUT shared_blks_dirtied bigint, OUT shared_blks_written bigint, OUT local_blks_hit bigint, OUT local_blks_read bigint, OUT local_blks_dirtied bigint, OUT local_blks_written bigint, OUT temp_blks_read bigint, OUT temp_blks_written bigint, OUT blk_read_time double precision, OUT blk_write_time double precision | normal | volatile | safe | postgres | invoker | | c | pg_stat_statements_1_3 |
(1 row)
peiybdb=# \d
List of relations
Schema | Name | Type | Owner
--------+--------------------+-------+----------
public | pg_stat_statements | view | postgres
peiybdb=# \d+ pg_stat_statements
View "public.pg_stat_statements"
Column | Type | Modifiers | Storage | Description
---------------------+------------------+-----------+----------+-------------
userid | oid | | plain |
dbid | oid | | plain |
queryid | bigint | | plain |
query | text | | extended |
calls | bigint | | plain |
total_time | double precision | | plain |
min_time | double precision | | plain |
max_time | double precision | | plain |
mean_time | double precision | | plain |
stddev_time | double precision | | plain |
rows | bigint | | plain |
shared_blks_hit | bigint | | plain |
shared_blks_read | bigint | | plain |
shared_blks_dirtied | bigint | | plain |
shared_blks_written | bigint | | plain |
local_blks_hit | bigint | | plain |
local_blks_read | bigint | | plain |
local_blks_dirtied | bigint | | plain |
local_blks_written | bigint | | plain |
temp_blks_read | bigint | | plain |
temp_blks_written | bigint | | plain |
blk_read_time | double precision | | plain |
blk_write_time | double precision | | plain |
View definition:
SELECT pg_stat_statements.userid,
pg_stat_statements.dbid,
pg_stat_statements.queryid,
pg_stat_statements.query,
pg_stat_statements.calls,
pg_stat_statements.total_time,
pg_stat_statements.min_time,
pg_stat_statements.max_time,
pg_stat_statements.mean_time,
pg_stat_statements.stddev_time,
pg_stat_statements.rows,
pg_stat_statements.shared_blks_hit,
pg_stat_statements.shared_blks_read,
pg_stat_statements.shared_blks_dirtied,
pg_stat_statements.shared_blks_written,
pg_stat_statements.local_blks_hit,
pg_stat_statements.local_blks_read,
pg_stat_statements.local_blks_dirtied,
pg_stat_statements.local_blks_written,
pg_stat_statements.temp_blks_read,
pg_stat_statements.temp_blks_written,
pg_stat_statements.blk_read_time,
pg_stat_statements.blk_write_time
FROM pg_stat_statements(true) pg_stat_statements(userid, dbid, queryid, query, calls, total_time, min_time, max_time, mean_time, stddev_time, rows, shared_blks_hit, shared_blks_read, shared_blks_dirtied, shared_blks_written, local_blks_hit, local_blks_read, local_blks_dirtied, local_blks_written, temp_blks_read, temp_blks_written, blk_read_time, blk_write_time);
可以使用 pg_stat_statements_reset() 函数来重置 pg_stat_statements，方便阶段性的分析慢sql，比如专项优化、大版本上线监控。
peiybdb=# select pg_stat_statements_reset();
pg_stat_statements_reset
--------------------------
(1 row)
peiybdb=#
peiybdb=#
peiybdb=# select count(1) from pg_stat_statements;
count
-------
1
(1 row)
查找top sql
top io sql
平均单次 io
select userid::regrole, dbid, query from pg_stat_statements order by (blk_read_time+blk_write_time)/calls desc limit 20;
累计 io
select userid::regrole, dbid, query from pg_stat_statements order by (blk_read_time+blk_write_time) desc limit 20;
top time sql
平均 time
select userid::regrole, dbid, query from pg_stat_statements order by mean_time desc limit 20;
累计 time
select userid::regrole, dbid, query from pg_stat_statements order by total_time desc limit 20;
不稳定，时快时慢
select userid::regrole, dbid, query from pg_stat_statements order by stddev_time desc limit 20;
top shared memory
select userid::regrole, dbid, query from pg_stat_statements order by (shared_blks_hit+shared_blks_dirtied) desc limit 20;
top temp memory
select userid::regrole, dbid, query from pg_stat_statements order by temp_blks_written desc limit 20;
参考：
http://postgres.cn/docs/9.6/pgstatstatements.html
https://blog.csdn.net/ctypyb2002/article/details/77711802