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 5.13 Running Multiple MySQL Servers on the Same Machine
 =======================================================
 

Menu

 
* multiple-windows-servers     Running Multiple Servers on Windows
* multiple-unix-servers        Running Multiple Servers on Unix
* multiple-server-clients      Using Client Programs in a Multiple-Server Environment
 
 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  program-options.
 
 At least the following options must be different for each server:
 
    * -port=PORT_NUM
 
      -port controls the port number for TCP/IP connections.
 
    * -socket=PATH
 
      -socket 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.
 
    * -shared-memory-base-name=NAME
 
      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.
 
    * -pid-file=FILE_NAME
 
      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:
 
    * -log=FILE_NAME
 
    * -log-bin=FILE_NAME
 
    * -log-update=FILE_NAME
 
    * -log-error=FILE_NAME
 
    * -bdb-logdir=FILE_NAME
 
  log-file-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:
 
    * -tmpdir=PATH
 
    * -bdb-tmpdir=PATH
 
 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 -datadir=PATH 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 `MyISAM' and `MERGE' 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 `lockd' 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
 -basedir=PATH 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 -socket and -port options.
 For example, suppose that you install different versions of MySQL using
 `tar' 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 -basedir option to pass to `mysqld', and you need
 specify only the -socket and -port 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 -defaults-file option is useful for this purpose.
 

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