E.1 Debugging a MySQL server

If you are using some functionality that is very new in MySQL, you can try to run mysqld with the --skip-new (which will disable all new, potentially unsafe functionality) or with --safe-mode which disables a lot of optimisation that may cause problems. See section A.4.1 What To Do If MySQL Keeps Crashing.

If mysqld doesn't want to start, you should check that you don't have any `my.cnf' files that interfere with your setup! You can check your `my.cnf' arguments with mysqld --print-defaults and avoid using them by starting with mysqld --no-defaults ....

If mysqld starts to eat up CPU or memory or if it ``hangs'', you can use mysqladmin processlist status to find out if someone is executing a query that takes a long time. It may be a good idea to run mysqladmin -i10 processlist status in some window if you are experiencing performance problems or problems when new clients can't connect.

The command mysqladmin debug will dump some information about locks in use, used memory and query usage to the mysql log file. This may help solve some problems. This command also provides some useful information even if you haven't compiled MySQL for debugging!

If the problem is that some tables are getting slower and slower you should try to optimise the table with OPTIMIZE TABLE or myisamchk. See section 4 Database Administration. You should also check the slow queries with EXPLAIN.

You should also read the OS-specific section in this manual for problems that may be unique to your environment. See section 2.6 Operating System Specific Notes.

Subsections

• E.1.1 Compiling MYSQL for Debugging
• E.1.2 Creating Trace Files
• E.1.3 Debugging mysqld under gdb
• E.1.4 Using a Stack Trace
• E.1.5 Using Log Files to Find Cause of Errors in mysqld
• E.1.6 Making a Test Case If You Experience Table Corruption

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