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24 MySQL internals

This chapter describes a lot of things that you need to know when working on the MySQL code.

24.1 MySQL threads

The MySQL server creates the the following threads:

The TCP/IP connection thread handles all connect requests and creates a new dedicated thread to handle the authentication and and SQL query processing for the connection.
On NT there is a named pipe handler thread that does the same work as the TCP/IP connection thread on named pipe connect requests.
The signal thread handles all signals. This thread also normally handles alarms and calls process_alarm() to force timeouts on connections that have been idle too long.
If compiled with -DUSE_ALARM_THREAD, a dedicated thread that handles alarms is created. This is only used on some systems where there are some problems with sigwait() or if one wants to use the thr_alarm() code in ones application without a dedicated signal handling thread.
If one uses the --flush-time option, a dedicated thread is created to flush all tables at the given interval.
Every connection has its own thread.
Every different table on which one uses INSERT DELAYED gets its own thread.
If you use --master-host , slave replication thread will be started to read and apply updates from the master.

mysqladmin processlist only shows the connection and INSERT DELAYED threads.