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$pgdata/postgresql.conf里面。 os:centos 6.2 db:postgre
postgres的日志实用功能
不得不说，postgres的日志(pg_log，类似oracle的alter文件，非pg_xlog)确实是很灵活，功能也很丰富的，下面是借用postgres的日志来实现一些管理功能，下面涉及的参数都在文件$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);
             now              | pg_sleep 
------------------------------+----------
 2013-03-29 12:36:48.13353-07 | 
(1 row)
time: 1001.844 ms
postgres=# select now(),pg_sleep(4);
              now              | pg_sleep 
-------------------------------+----------
 2013-03-29 12:36:28.309595-07 | 
(1 row)
time: 4002.273 ms
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv 
2013-03-29 12:36:19.265 pdt,postgres,postgres,2324,[local],5155d681.914,10,select,2013-03-29 10:59:29 pdt,2/0,0,log,00000,duration: 4027.183 ms  statement: select now(),pg_sleep(4);,,,,,,,,,psql
可以看到只记录了4秒的那个sql，而没有记录1秒的sql。
3.监控数据库的checkpoint 
当数据库进行一项大更新操作时，如果参数设置不当，会在日志里留下大量的告警信息，频繁的做checkpoint会导致系统变慢，如:
2013-03-28 17:01:39.523 cst,,,10350,,50bd676b.286e,1,,2012-12-04 11:00:59 cst,,0,log,00000,checkpoints are occurring too frequently (8 seconds apart),,consider increasing the configuration parameter checkpoint_segments.,,,,,,,
2013-03-28 17:01:50.427 cst,,,10350,,50bd676b.286e,2,,2012-12-04 11:00:59 cst,,0,log,00000,checkpoints are occurring too frequently (11 seconds apart),,consider increasing the configuration parameter checkpoint_segments.,,,,,,,
但是不会记录系统正常的checkpoint，如果你想看系统一天之类发生了多少次checkpoint，以及每次checkpoint的一些详细信息，比如buffer,sync等，就可以通过设置log_checkpoints，该参数默认值是off，修改log_checkpoints = on 示例：
postgres=# show log_checkpoints ;
 log_checkpoints 
-----------------
 on
(1 row)
postgres=# checkpoint;
checkpoint
postgres=#
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv 
2013-03-29 12:43:38.900 pdt,,,5557,,514933a7.15b5,45,,2013-03-19 20:57:27 pdt,,0,log,00000,checkpoint starting: immediate force wait,,,,,,,,,
2013-03-29 12:43:38.941 pdt,,,5557,,514933a7.15b5,46,,2013-03-19 20:57:27 pdt,,0,log,00000,checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s) added, 0 removed, 0 recycled; write=0.009 s, sync=0.000 s, total=0.040 s; sync files=0, longest=0.000 s, average=0.000 s,,,,,,,,,
4.监控数据库的锁 
数据库的锁通常可以在pg_locks这个系统表里找，但这只是当前的锁表/行信息，如果你想看一天内有多少个超过死锁时间的锁发生，可以在日志里设置并查看，log_lock_waits 默认是off，可以设置开启。这个可以区分sql慢是资源紧张还是锁等待的问题。 示例:
postgres=# show log_lock_waits ;
 log_lock_waits 
----------------
 on
(1 row)
postgres=# show deadlock_timeout ;
 deadlock_timeout 
------------------
 1s
(1 row)
--模拟锁
postgres=# begin;
begin
postgres=# select * from t_ken_yon ;
 id 
----
 11
(1 row)
postgres=# delete from t_ken_yon ;
delete 1
--另一个session
postgres=# begin;
begin
postgres=# delete from t_ken_yon;
--查看日志
[postgres@localhost pg_log]$ tail -f postgresql-2013-03-29_000000.csv
2013-03-29 14:01:02.673 pdt,postgres,postgres,3056,[local],5155f4d9.bf0,6,delete waiting,2013-03-29 13:08:57 pdt,5/12502,2659,log,00000,process 3056 still waiting for sharelock on transaction 2658 after 1000.398 ms,,,,,,delete from t_ken_yon;,,,psql
2013-03-29 14:02:06.208 pdt,postgres,postgres,3056,[local],5155f4d9.bf0,7,delete waiting,2013-03-29 13:08:57 pdt,5/12502,2659,log,00000,process 3056 acquired sharelock on transaction 2658 after 64535.339 ms,,,,,,delete from t_ken_yon;,,,psql
2013-03-29 14:02:06.209 pdt,postgres,postgres,3056,[local],5155f4d9.bf0,8,delete,2013-03-29 13:08:57 pdt,5/12502,2659,log,00000,duration: 64536.118 ms  statement: delete from t_ken_yon;,,,,,,,,,psql
还有一些debug功能，适合修改源码调试，一般的的系统上并不需要，暂时比较关注的就这些。