Postgres的日志实用功能
Postgres的日志实用功能
不得不说，Postgres的日志(pg_log，类似oracle的alter文件，非pg_xlog)确实是很灵活，功能也很丰富的，下面是借用postgres的日志来实现一些管理功能，下面涉及的参数都在文件$PGDATA/postgresql.conf里面。
OS:CentOS 6.2
DB:Postgres 9.2.3
1.日志审计
审计是值记录用户的登陆退出以及登陆后在数据库里的行为操作，可以根据安全等级不一样设置不一样级别的审计，
此处涉及的参数文件有：
logging_collector --是否开启日志收集开关，默认off，开启要重启DB
log_destination --日志记录类型，默认是stderr，只记录错误输出
log_directory --日志路径，默认是$PGDATA/pg_log
log_filename --日志名称，默认是postgresql-%Y-%m-%d_%H%M%S.log
log_connections --用户session登陆时是否写入日志，默认off
log_disconnections --用户session退出时是否写入日志，默认off
log_rotation_age --保留单个文件的最大时长,默认是1d,也有1h,1min,1s,个人觉得不实用
log_rotation_size --保留单个文件的最大尺寸，默认是10MB
配置值：
logging_collector = on
log_destination = 'csvlog'
log_directory = '/home/postgres/pg_log'
log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'
log_connections = on
log_disconnections = on
log_rotation_age = 1d
log_rotation_size = 20MB
配置完重启DB，检查日志情况
[postgres@localhost pg_log]$ ls -l
total 4
-rw-------. 1 postgres postgres 672 Mar 29 08:25 postgresql-2013-03-29_000000.csv
-rw-------. 1 postgres postgres 0 Mar 29 00:00 postgresql-2013-03-29_000000.log
[postgres@localhost pg_log]$
--登陆并退出，日志内容有访问的IP(local),访问用户，登陆和退出时间等信息，对检查超级用户的登陆退出是很有效的
[postgres@localhost pg_log]$ psql
psql (9.2.3)
Type "help" for help.
postgres=# \q
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv
2013-03-29 10:38:36.934 PDT,,,2236,"",5155d19c.8bc,1,"",2013-03-29 10:38:36 PDT,,0,LOG,00000,"connection received: host=[local]",,,,,,,,,""
2013-03-29 10:38:36.938 PDT,"postgres","postgres",2236,"[local]",5155d19c.8bc,2,"authentication",2013-03-29 10:38:36 PDT,2/11858,0,LOG,00000,"connection authorized: user=postgres database=postgres",,,,,,,,,""
2013-03-29 10:38:42.365 PDT,"postgres","postgres",2236,"[local]",5155d19c.8bc,3,"idle",2013-03-29 10:38:36 PDT,,0,LOG,00000,"disconnection: session time: 0:00:05.431 user=postgres database=postgres host=[local]",,,,,,,,,"psql"
记录用户登陆数据库后的各种操作，postgres日志里分成了3类，通过参数pg_statement来控制，默认的pg_statement参数值是none，即不记录，可以设置ddl(记录create,drop和alter)、mod(记录ddl+insert,delete,update和truncate)和all(mod+select)。
示例：
[postgres@localhost ~]$ vi $PGDATA/postgresql.conf
log_statement = ddl
postgres=# show log_statement;
log_statement
---------------
ddl
(1 row)
postgres=# create table t_ken_yon(id int);
CREATE TABLE
postgres=# drop table t_ken_yon ;
DROP TABLE
postgres=#
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv
2013-03-29 11:01:29.048 PDT,"postgres","postgres",2324,"[local]",5155d681.914,3,"idle",2013-03-29 10:59:29 PDT,2/11945,0,LOG,00000,"statement: create table t_ken_yon(id int);",,,,,,,,,"psql"
2013-03-29 11:01:36.087 PDT,"postgres","postgres",2324,"[local]",5155d681.914,4,"idle",2013-03-29 10:59:29 PDT,2/11948,0,LOG,00000,"statement: drop table t_ken_yon ;",,,,,,,,,"psql"
--修改为mod级别，并reload
postgres=# show log_statement;
log_statement
---------------
mod
(1 row)
postgres=# insert into t_ken_yon values(1),(2);
INSERT 0 2
postgres=# delete from t_ken_yon where id =1;
DELETE 1
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv
2013-03-29 11:04:08.148 PDT,,,5554,,514933a6.15b2,42,,2013-03-19 20:57:26 PDT,,0,LOG,00000,"received SIGHUP, reloading configuration files",,,,,,,,,""
2013-03-29 11:04:08.151 PDT,,,5554,,514933a6.15b2,43,,2013-03-19 20:57:26 PDT,,0,LOG,00000,"parameter ""log_statement"" changed to ""mod""",,,,,,,,,""
2013-03-29 11:05:33.346 PDT,"postgres","postgres",2324,"[local]",5155d681.914,6,"idle",2013-03-29 10:59:29 PDT,2/11952,0,LOG,00000,"statement: insert into t_ken_yon values(1),(2);",,,,,,,,,"psql"
2013-03-29 11:05:52.033 PDT,"postgres","postgres",2324,"[local]",5155d681.914,7,"idle",2013-03-29 10:59:29 PDT,2/11953,0,LOG,00000,"statement: delete from t_ken_yon where id =1;",,,,,,,,,"psql"
--修改为all级别，并reload
postgres=# show log_statement;
log_statement
---------------
all
(1 row)
postgres=# select * from t_ken_yon;
id
----
2
(1 row)
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv
2013-03-29 11:07:14.820 PDT,,,5554,,514933a6.15b2,44,,2013-03-19 20:57:26 PDT,,0,LOG,00000,"received SIGHUP, reloading configuration files",,,,,,,,,""
2013-03-29 11:07:14.821 PDT,,,5554,,514933a6.15b2,45,,2013-03-19 20:57:26 PDT,,0,LOG,00000,"parameter ""log_statement"" changed to ""all""",,,,,,,,,""
2013-03-29 11:07:19.784 PDT,"postgres","postgres",2324,"[local]",5155d681.914,8,"idle",2013-03-29 10:59:29 PDT,2/11954,0,LOG,00000,"statement: show log_statement;",,,,,,,,,"psql"
2013-03-29 11:07:28.631 PDT,"postgres","postgres",2324,"[local]",5155d681.914,9,"idle",2013-03-29 10:59:29 PDT,2/11955,0,LOG,00000,"statement: select * from t_ken_yon;",,,,,,,,,"psql"
一般的OLTP系统审计级别设置为ddl就够了，因为记录输出各种SQL对性能的影响还是蛮大的，安全级别高一点的也可以设置mod模式，有条件也可以不在数据库层面做，而是购买设备放在网络层监控解析。
2.定位慢查询SQL
可以设置一定时长的参数(log_min_duration_statement)，来记录超过该时长的所有SQL，对找出当前数据库的慢查询很有效。 比如log_min_duration_statement = 2s,记录超过2秒的SQL，改完需要reload
示例:
postgres=# show log_min_duration_statement ;
log_min_duration_statement
----------------------------
2s
(1 row)
postgres=# \timing
Timing is on.
postgres=# select now(),pg_sleep(1);
