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$PGDATA/postgresql.conf里面。
OS:CentOS 6.2
DB:Postgres 9.2.3
1.日志审计
审计是值记录用户的登陆退出以及登陆后在数据库里的行为操作，可以根据安全等级不一样设置不一样级别的审计，
此处涉及的参数文件有：
示例：
[postgres@localhost ~]$ vi $PGDATA/postgresql.conf
log_statement = ddl
2.定位慢查询SQL
可以设置一定时长的参数(log_min_duration_statement)，来记录超过该时长的所有SQL，对找出当前数据库的慢查询很有效。 比如log_min_duration_statement = 2s,记录超过2秒的SQL，改完需要reload
示例:
3.监控数据库的checkpoint
当数据库进行一项大更新操作时，如果参数设置不当，会在日志里留下大量的告警信息，频繁的做checkpoint会导致系统变慢，如:
4.监控数据库的锁
数据库的锁通常可以在pg_locks这个系统表里找，但这只是当前的锁表/行信息，如果你想看一天内有多少个超过死锁时间的锁发生，可以在日志里设置并查看，log_lock_waits 默认是off，可以设置开启。这个可以区分SQL慢是资源紧张还是锁等待的问题。 示例:
OS:CentOS 6.2
DB:Postgres 9.2.3
1.日志审计
审计是值记录用户的登陆退出以及登陆后在数据库里的行为操作，可以根据安全等级不一样设置不一样级别的审计，
此处涉及的参数文件有：
logging_collector --是否开启日志收集开关，默认off，开启要重启DB log_destination --日志记录类型，默认是stderr，只记录错误输出 log_directory --日志路径，默认是$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。