postgresql 查詢慢sql之二: pg_stat_statements
阿新 • • 發佈：2018-12-16
pg_stat_statements模組提供一種方法追蹤一個伺服器所執行的所有 SQL 語句的執行統計資訊。
該模組必須通過在 postgresql.conf 的 shared_preload_libraries 中增加pg_stat_statements 來載入，因為它需要額外的共享記憶體。這意味著增加或移除該模組需要一次伺服器重啟。
當 pg_stat_statements 被載入時，它會跟蹤該伺服器 的所有資料庫的統計資訊。該模組提供了一個檢視 pg_stat_statements 以及函式 pg_stat_statements_reset 和pg_stat_statements 用於訪問和操縱這些統計資訊。這些檢視 和函式不是全域性可用的，但是可以用 CREATE EXTENSION pg_stat_statements 為特定資料庫啟用它們。
apt 、yum 安裝
需要安裝相同版本的contrib包，以ubuntu為例。
# 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
原始碼編譯安裝
編譯安裝時如果是如下方式，則已經安裝了。
$ make world $ make install-world
否則，需要進入到原始碼的 \contrib\pg_stat_statements\ 下單獨編譯安裝
$ cd /tmp/postgresql-9.6.8\contrib\pg_stat_statements\
$ make
$ make install
建立 pg_stat_statements
需要修改 postgrsql.conf 的 shared_preload_libraries 值後，重啟postgresql。
$ vi postgresql.conf shared_preload_libraries = 'pg_stat_statements' # (change requires restart) # systemctl stop postgresql # systemctl start postgresql
由於pg_stat_statements針對的是資料庫級別，所以需要首先進入指定資料庫
postgres=# \c peiybdb
peiybdb=# create extension pg_stat_statements；
建立好後，會多出一個檢視 pg_stat_statements
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() 函式來重置 pg_stat_statements，方便階段性的分析慢sql，比如專項優化、大版本上線監控。
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)