5.13. Running Multiple MySQL Servers on the Same Machine

MySQL 5.0

5.13. Running Multiple MySQL Servers on the Same Machine

In some cases, you might want to run multiple mysqld servers on the same machine. You might want to test a new MySQL release while leaving your existing production setup undisturbed. Or you might want to give different users access to different mysqld servers that they manage themselves. (For example, you might be an Internet Service Provider that wants to provide independent MySQL installations for different customers.)

To run multiple servers on a single machine, each server must have unique values for several operating parameters. These can be set on the command line or in option files. See Section 4.3, “Specifying Program Options”.

At least the following options must be different for each server:

  • controls the port number for TCP/IP connections.

  • controls the Unix socket file path on Unix and the name of the named pipe on Windows. On Windows, it is necessary to specify distinct pipe names only for those servers that support named-pipe connections.

  • This option currently is used only on Windows. It designates the shared-memory name used by a Windows server to allow clients to connect via shared memory. It is necessary to specify distinct shared-memory names only for those servers that support shared-memory connections.

  • This option is used only on Unix. It indicates the pathname of the file in which the server writes its process ID.

If you use the following log file options, they must be different for each server:

Section 5.12.5, “Server Log Maintenance”, discusses the log file options further.

For better performance, you can specify the following options differently for each server, to spread the load between several physical disks:

Having different temporary directories is also recommended to make it easier to determine which MySQL server created any given temporary file.

With very limited exceptions, each server should use a different data directory, which is specified using the option.

Warning: Normally, you should never have two servers that update data in the same databases. This may lead to unpleasant surprises if your operating system does not support fault-free system locking. If (despite this warning) you run multiple servers using the same data directory and they have logging enabled, you must use the appropriate options to specify log filenames that are unique to each server. Otherwise, the servers try to log to the same files. Please note that this kind of setup only works with and tables, and not with any of the other storage engines.

The warning against sharing a data directory among servers also applies in an NFS environment. Allowing multiple MySQL servers to access a common data directory over NFS is a very bad idea.

  • The primary problem is that NFS is the speed bottleneck. It is not meant for such use.

  • Another risk with NFS is that you must devise a way to ensure that two or more servers do not interfere with each other. Usually NFS file locking is handled by the daemon, but at the moment there is no platform that performs locking 100% reliably in every situation.

Make it easy for yourself: Forget about sharing a data directory among servers over NFS. A better solution is to have one computer that contains several CPUs and use an operating system that handles threads efficiently.

If you have multiple MySQL installations in different locations, you can specify the base installation directory for each server with the option to cause each server to use a different data directory, log files, and PID file. (The defaults for all these values are determined relative to the base directory). In that case, the only other options you need to specify are the and options. For example, suppose that you install different versions of MySQL using file binary distributions. These install in different locations, so you can start the server for each installation using the command bin/mysqld_safe under its corresponding base directory. mysqld_safe determines the proper option to pass to mysqld, and you need specify only the and options to mysqld_safe.

As discussed in the following sections, it is possible to start additional servers by setting environment variables or by specifying appropriate command-line options. However, if you need to run multiple servers on a more permanent basis, it is more convenient to use option files to specify for each server those option values that must be unique to it. The option is useful for this purpose.

5.13.1. Running Multiple Servers on Windows

You can run multiple servers on Windows by starting them manually from the command line, each with appropriate operating parameters. On Windows NT-based systems, you also have the option of installing several servers as Windows services and running them that way. General instructions for running MySQL servers from the command line or as services are given in Section 2.3, “Installing MySQL on Windows”. This section describes how to make sure that you start each server with different values for those startup options that must be unique per server, such as the data directory. These options are described in Section 5.13, “Running Multiple MySQL Servers on the Same Machine”.

5.13.1.1. Starting Multiple Windows Servers at the Command Line

To start multiple servers manually from the command line, you can specify the appropriate options on the command line or in an option file. It is more convenient to place the options in an option file, but it is necessary to make sure that each server gets its own set of options. To do this, create an option file for each server and tell the server the filename with a option when you run it.

Suppose that you want to run mysqld on port 3307 with a data directory of , and mysqld-max on port 3308 with a data directory of . (To do this, make sure that before you start the servers, each data directory exists and has its own copy of the database that contains the grant tables.) Then create two option files. For example, create one file named that looks like this:

[mysqld]
datadir = C:/mydata1
port = 3307

Create a second file named that looks like this:

[mysqld]
datadir = C:/mydata2
port = 3308

Then start each server with its own option file:

C:\> 
C:\> 

On NT, each server starts in the foreground (no new prompt appears until the server exits later), so you will need to issue those two commands in separate console windows.

To shut down the servers, you must connect to each using the appropriate port number:

C:\> 
C:\> 

Servers configured as just described allow clients to connect over TCP/IP. If your version of Windows supports named pipes and you also want to allow named-pipe connections, use the mysqld-nt or mysqld-max-nt servers and specify options that enable the named pipe and specify its name. Each server that supports named-pipe connections must use a unique pipe name. For example, the file might be written like this:

[mysqld]
datadir = C:/mydata1
port = 3307
enable-named-pipe
socket = mypipe1

Then start the server this way:

C:\> 

Modify similarly for use by the second server.

A similar procedure applies for servers that you want to support shared-memory connections. Enable such connections with the option and specify a unique shared-memory name for each server with the option.

5.13.1.2. Starting Multiple Windows Servers as Services

On NT-based systems, a MySQL server can run as a Windows service. The procedures for installing, controlling, and removing a single MySQL service are described in Section 2.3.11, “Starting MySQL as a Windows Service”.

You can also install multiple MySQL servers as services. In this case, you must make sure that each server uses a different service name in addition to all the other parameters that must be unique for each server.

For the following instructions, assume that you want to run the mysqld-nt server from two different versions of MySQL that are installed at and , respectively. (This might be the case if you're running 4.1.8 as your production server, but also want to conduct tests using 5.0.25.)

The following principles apply when installing a MySQL service with the or option:

  • If you specify no service name, the server uses the default service name of and the server reads options from the group in the standard option files.

  • If you specify a service name after the option, the server ignores the option group and instead reads options from the group that has the same name as the service. The server reads options from the standard option files.

  • If you specify a option after the service name, the server ignores the standard option files and reads options only from the group of the named file.

Note: Before MySQL 4.0.17, only a server installed using the default service name () or one installed explicitly with a service name of mysqld read the group in the standard option files. As of 4.0.17, all servers read the group if they read the standard option files, even if they are installed using another service name. This allows you to use the group for options that should be used by all MySQL services, and an option group named after each service for use by the server installed with that service name.

Based on the preceding information, you have several ways to set up multiple services. The following instructions describe some examples. Before trying any of them, be sure that you shut down and remove any existing MySQL services first.

  • Approach 1: Specify the options for all services in one of the standard option files. To do this, use a different service name for each server. Suppose that you want to run the 4.1.8 mysqld-nt using the service name of and the 5.0.25 mysqld-nt using the service name . In this case, you can use the group for 4.1.8 and the group for 5.0.25. For example, you can set up like this:

    # options for mysqld1 service
    [mysqld1]
    basedir = C:/mysql-4.1.8
    port = 3307
    enable-named-pipe
    socket = mypipe1
    
    # options for mysqld2 service
    [mysqld2]
    basedir = C:/mysql-5.0.25
    port = 3308
    enable-named-pipe
    socket = mypipe2
    

    Install the services as follows, using the full server pathnames to ensure that Windows registers the correct executable program for each service:

    C:\> 
    C:\> 
    

    To start the services, use the services manager, or use NET START with the appropriate service names:

    C:\> 
    C:\> 
    

    To stop the services, use the services manager, or use NET STOP with the appropriate service names:

    C:\> 
    C:\> 
    
  • Approach 2: Specify options for each server in separate files and use when you install the services to tell each server what file to use. In this case, each file should list options using a group.

    With this approach, to specify options for the 4.1.8 mysqld-nt, create a file that looks like this:

    [mysqld]
    basedir = C:/mysql-4.1.8
    port = 3307
    enable-named-pipe
    socket = mypipe1
    

    For the 5.0.25 mysqld-nt, create a file that looks like this:

    [mysqld]
    basedir = C:/mysql-5.0.25
    port = 3308
    enable-named-pipe
    socket = mypipe2
    

    Install the services as follows (enter each command on a single line):

    C:\> 
               
    C:\> 
               
    

    To use a option when you install a MySQL server as a service, you must precede the option with the service name.

    After installing the services, start and stop them the same way as in the preceding example.

To remove multiple services, use mysqld --remove for each one, specifying a service name following the option. If the service name is the default (), you can omit it.

5.13.2. 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 4.1.8 server is configured for the default TCP/IP port number (3306) and Unix socket file (). To configure a new 5.0.25 server to have different operating parameters, use a configure command something like this:

shell>  \
              \
             

Here, and must be different from the default TCP/IP port number and Unix socket file pathname, and the 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>  --port= 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 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 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>  --port=

To start a second server, provide different and option values, and pass a 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> 
shell> 
shell> 
shell> 
shell> 

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> 

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 5.4.3, “mysqld_multi — Manage Multiple MySQL Servers”.

5.13.3. Using Client Programs in a Multiple-Server Environment

To connect with a client program to a MySQL server that is listening to different network interfaces from those compiled into your client, you can use one of the following methods:

  • Start the client with --port= to connect via TCP/IP to a remote server, with to connect via TCP/IP to a local server, or with to connect to a local server via a Unix socket file or a Windows named pipe.

  • As of MySQL 4.1, start the client with to connect via TCP/IP, to connect via a Unix socket file, to connect via a named pipe, or to connect via shared memory. For TCP/IP connections, you may also need to specify and options. For the other types of connections, you may need to specify a option to specify a Unix socket file or Windows named-pipe name, or a option to specify the shared-memory name. Shared-memory connections are supported only on Windows.

  • On Unix, set the and environment variables to point to the Unix socket file and TCP/IP port number before you start your clients. If you normally use a specific socket file or port number, you can place commands to set these environment variables in your file so that they apply each time you log in. See Appendix F, Environment Variables.

  • Specify the default Unix socket file and TCP/IP port number in the group of an option file. For example, you can use on Windows, or the file in your home directory on Unix. See Section 4.3.2, “Using Option Files”.

  • In a C program, you can specify the socket file or port number arguments in the call. You can also have the program read option files by calling . See Section 22.2.3, “C API Function Descriptions”.

  • If you are using the Perl module, you can read options from MySQL option files. For example:

    $dsn = "DBI:mysql:test;mysql_read_default_group=client;"
            . "mysql_read_default_file=/usr/local/mysql/data/my.cnf";
    $dbh = DBI->connect($dsn, $user, $password);
    

    See Section 22.4, “MySQL Perl API”.

    Other programming interfaces may provide similar capabilities for reading option files.