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2.8.5. MIT-pthreads Notes

This section describes some of the issues involved in using MIT-pthreads.

On Linux, you should not use MIT-pthreads. Use the installed LinuxThreads implementation instead. See Section 2.12.1, “Linux Notes”.

If your system does not provide native thread support, you should build MySQL using the MIT-pthreads package. This includes older FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others. See Section 2.1.1, “Operating Systems Supported by MySQL”.

MIT-pthreads is not part of the MySQL 5.1 source distribution. If you require this package, you need to download it separately from http://www.mysql.com/Downloads/Contrib/pthreads-1_60_beta6-mysql.tar.gz

After downloading, extract this source archive into the top level of the MySQL source directory. It creates a new subdirectory named mit-pthreads.

  • On most systems, you can force MIT-pthreads to be used by running configure with the --with-mit-threads option:

    shell> ./configure --with-mit-threads
    

    Building in a non-source directory is not supported when using MIT-pthreads because we want to minimize our changes to this code.

  • The checks that determine whether to use MIT-pthreads occur only during the part of the configuration process that deals with the server code. If you have configured the distribution using --without-server to build only the client code, clients do not know whether MIT-pthreads is being used and use Unix socket file connections by default. Because Unix socket files do not work under MIT-pthreads on some platforms, this means you need to use -h or --host with a value other than localhost when you run client programs.

  • When MySQL is compiled using MIT-pthreads, system locking is disabled by default for performance reasons. You can tell the server to use system locking with the --external-locking option. This is needed only if you want to be able to run two MySQL servers against the same data files, but that is not recommended, anyway.

  • Sometimes the pthread bind() command fails to bind to a socket without any error message (at least on Solaris). The result is that all connections to the server fail. For example:

    shell> mysqladmin version
    mysqladmin: connect to server at '' failed;
    error: 'Can't connect to mysql server on localhost (146)'
    

    The solution to this problem is to kill the mysqld server and restart it. This has happened to us only when we have forcibly stopped the server and restarted it immediately.

  • With MIT-pthreads, the sleep() system call isn't interruptible with SIGINT (break). This is noticeable only when you run mysqladmin --sleep. You must wait for the sleep() call to terminate before the interrupt is served and the process stops.

  • When linking, you might receive warning messages like these (at least on Solaris); they can be ignored:

    ld: warning: symbol `_iob' has differing sizes:
        (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
    file /usr/lib/libc.so value=0x140);
        /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
    ld: warning: symbol `__iob' has differing sizes:
        (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
    file /usr/lib/libc.so value=0x140);
        /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
    
  • Some other warnings also can be ignored:

    implicit declaration of function `int strtoll(...)'
    implicit declaration of function `int strtoul(...)'
    
  • We have not been able to make readline work with MIT-pthreads. (This is not necessary, but may be of interest to some.)


 
 
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