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 may 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 3.3, "Specifying Program Options."
At least the following options must be different for each server:
If you use the following log file options, they must be different for each server:
Log file options are described in Section 4.8.6, "Log File Maintenance."
If you want more performance, you can also 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.
Generally, each server should also 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 doesn't 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 file names that are unique to each server. Otherwise, the servers will try to log to the same files.
This 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 bad idea!
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, normally 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 will 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 will determine the proper --basedir option to pass to mysqld, and you need specify only the --socket and --port options to mysqld_safe. (For versions of MySQL older than 4.0, use safe_mysqld rather than 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 will be more convenient to use option files to specify for each server those option values that must be unique to it.
4.9.1 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 2.2.1, "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 4.9, "Running Multiple MySQL Servers on the Same Machine."
126.96.36.199 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's more convenient to place the options in an option file, but it's 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 --defaults-file option when you run it.
Suppose that you want to run mysqld on port 3307 with a data directory of C:\mydata1, and mysqld-max on port 3308 with a data directory of C:\mydata2. (To do this, make sure that before you start the servers, each data directory exists and has its own copy of the mysql database that contains the grant tables.)
Then create two option files. For example, create one file named C:\my-opts1.cnf that looks like this:
[mysqld] datadir = C:/mydata1 port = 3307
Create a second file named C:\my-opts2.cnf that looks like this:
[mysqld] datadir = C:/mydata2 port = 3308
Then start each server with its own option file:
On NT, each server will start in the foreground (no new prompt appears until the server exits later); you'll need to issue those two commands in separate console windows.
To shut down the servers, you must connect to the appropriate port number:
C:\> C:\mysql\bin\mysqladmin --port=3307 shutdown C:\> C:\mysql\bin\mysqladmin --port=3308 shutdown
Servers configured as just described will 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 C:\my-opts1.cnf file might be written like this:
[mysqld] datadir = C:/mydata1 port = 3307 enable-named-pipe socket = mypipe1
Then start the server this way:
Modify C:\my-opts2.cnf similarly for use by the second server.
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