5.12.2. 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 Unix socket files so that
each one is listening on different network interfaces. Compiling
in different base directories for each installation also results
automatically in a separate, compiled-in data directory, log
file, and PID file location for each server.
Assume that an existing 5.0.19 server is configured for the
default TCP/IP port number (3306) and Unix socket file
(/tmp/mysql.sock). To configure a new
5.1.7-beta 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-5.1.7-beta
Here, port_number and
file_name must be different from the
default TCP/IP port number and Unix socket file pathname, and
the --prefix value should specify an
installation directory different from 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 Unix socket
filename:
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 defaults to using a Unix
socket file connection rather than TCP/IP. From MySQL 4.1
onward, 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 Unix socket file and TCP/IP port number. It is also
possible to use the same server binary and start each invocation
of it with different parameter values at runtime. One way to do
so is by using command-line options:
shell> mysqld_safe --socket=file_name --port=port_number
To start a second server, provide different
--socket and --port option
values, and pass a
--datadir=path
option to mysqld_safe so that the server uses
a different data directory.
Another way to achieve a similar effect is to use environment
variables to set the Unix socket filename and TCP/IP port
number:
shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock
shell> MYSQL_TCP_PORT=3307
shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT
shell> mysql_install_db --user=mysql
shell> mysqld_safe --datadir=/path/to/datadir &
This is a quick way of starting a second server to use for
testing. The nice thing about this method is that the
environment variable settings apply to any client programs that
you invoke from the same shell. Thus, connections for those
clients are automatically directed to the second server.
Appendix F, Environment Variables, includes a list of
other environment variables you can use to affect
mysqld.
For automatic server execution, the 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:
shell> mysqld_safe --defaults-file=file_name
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 5.3.3, “mysqld_multi — Manage Multiple MySQL Servers”.
