4.1.3.2 Running Multiple Servers on Unix

The easiest way is to run multiple servers on Unix is to compile them with different TCP/IP ports and socket files so that each one is listening on different network interfaces. Also, by compiling in different base directories for each installation, that automatically results in different compiled-in data directory, log file, and PID file locations for each of your servers.

Assume an existing server is configured for the default port number and socket file. To configure a new server to have different operating parameters, use a configure command something like this:

shell> ./configure --with-tcp-port=port_number \
             --with-unix-socket-path=file_name \
             --prefix=/usr/local/mysql-4.0.14

Here port_number and file_name should be different from the default port number and socket file pathname, and the --prefix value should specify an installation directory different than the one under which the existing MySQL installation is located.

If you have a MySQL server listening on a given port number, you can use the following command to find out what operating parameters it is using for several important configurable variables, including the base directory and socket name:

shell> mysqladmin --host=host_name --port=port_number variables

With the information displayed by that command, you can tell what option values not to use when configuring an additional server.

Note that if you specify ``localhost'' as a hostname, mysqladmin will default to using a Unix socket connection rather than TCP/IP. In MySQL 4.1, you can explicitly specify the connection protocol to use by using the --protocol={TCP | SOCKET | PIPE | MEMORY} option.

You don't have to compile a new MySQL server just to start with a different socket file and TCP/IP port number. It is also possible to specify those values at runtime. One way to do so is by using command-line options:

shell> /path/to/mysqld_safe --socket=file_name --port=port_number

To use another database directory for the second server, pass a --datadir=path option to mysqld_safe.

Another way to achieve a similar effect is to use environment variables to set the socket name and port number:

shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock
shell> MYSQL_TCP_PORT=3307
shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT
shell> scripts/mysql_install_db
shell> bin/mysqld_safe &

This is a quick and dirty method for starting a second server to use for testing. The nice thing about this method is that the environment variable settings will apply to any client programs that you invoke from the above shell. Thus, connections for those clients automatically will be directed to the second server!

section F Environment Variables includes a list of other environment variables you can use to affect mysqld.

For automatic server execution, your startup script that is executed at boot time should execute the following command once for each server with an appropriate option file path for each command:

mysqld_safe --defaults-file=path-to-option-file

Each option file should contain option values specific to a given server.

On Unix, the mysqld_multi script is another way to start multiple servers. See section 4.7.3 mysqld_multi, A Program for Managing Multiple MySQL Servers.

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