MySQL FAQs - Server Daemon mysqld Administration

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By: FYIcenter.com

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How To Turn on Query Logs?

If you want MySQL to write query logs to a file, you can use the "--log=fileName" option at the "mysqld" command line. The tutorial exercise below shows you a good example on how to use this option and view the query log file:

>cd \mysql\bin
>mkdir \mysql\logs
>mysqld --log=\mysql\logs\query.log

Starts another command window, and enter the following commands:

>cd \mysql\bin
>mysql -u root -pretneciyf

mysql> USE test;
Database changed

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| articles       |
| links          |
| test           |
+----------------+
3 rows in set (0.03 sec)

mysql> SELECT * FROM links;
+------+-------------------+
| id   | name              |
+------+-------------------+
|    1 | dba.fyicenter.com |
|   10 | dba.fyicenter.com |
+------+-------------------+
2 rows in set (0.11 sec)

mysql> EXIT;
Bye

Here is what you will get in the query log file:

>type \mysql\logs\query.log

mysqld, Version: 5.0.24-community-log. started with:
Tcp port: 0  Unix socket: (null)
Time                 Id Command    Argument
20:19:41	      3 Connect     root@localhost on 
20:20:00	      3 Query       SELECT DATABASE()
    		      3 Init DB     test
20:20:05	      3 Query       show tables
20:20:52	      3 Query       SELECT * FROM links
20:21:02	      3 Quit

How To Turn on Error Logs?

If you want MySQL to write critical errors into a log file, you can use the "--log-error=fileName" option at the "mysqld" command line. The tutorial exercise below shows you a good example on how to use this option:

>cd \mysql\bin
>mkdir \mysql\logs
>mysqld --log-error=\mysql\logs\error.log

If there is critical errors, your error log will be pretty empty:

>type \mysql\logs\error.log

20:32:21  InnoDB: Started; log sequence number 0 43665
20:32:21 [Note] mysqld: ready for connections.
Version: '5.0.24-community-log'  socket: ''  port: 3306

What Is Binary Log File?

MySQL server binary log file plays an important role in restoring database changes to the server. Main features on binary log files are:

Binary logs can be turned on by "--log-bin=fileBaseName" option on "mysqld".
Binary logs only records statements that are changing data in the database. So a simple SELECT statement will be not recorded in binary logs.
Binary logs are organized in multiple files with names like: base.index, base.000001, base.000002, etc. Each time when you restart the server, a new binary log file will be created.
Binary log files can be viewed by "mysqlbinlog" program.
Binary log files can be piped into back to the server as "mysqlbinlog base.000001 | mysql" for restoring data changes after a server crash.

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