MySQL 5.1 Reference Manual  /  ...  /  Windows Platform Limitations

C.7.6 Windows Platform Limitations

The following limitations apply to use of MySQL on the Windows platform:

  • Number of file descriptors

    The number of open file descriptors on Windows is limited to a maximum of 2048, which may limit the ability to open a large number of tables simultaneously. This limit is due not to Windows but to C runtime library compatibility functions used to open files on Windows that use the POSIX compatibility layer.

    This limitation will also cause problems if you try to set open_files_limit to a value greater than the 2048 file limit.

  • Process memory

    On Windows 32-bit platforms it is not possible by default to use more than 2GB of RAM within a single process, including MySQL. This is because the physical address limit on Windows 32-bit is 4GB and the default setting within Windows is to split the virtual address space between kernel (2GB) and user/applications (2GB).

    Some versions of Windows have a boot time setting to enable larger applications by reducing the kernel application. Alternatively, to use more than 2GB, use a 64-bit version of Windows.

  • File system aliases

    When using MyISAM tables, you cannot use aliases within Windows link to the data files on another volume and then link back to the main MySQL datadir location.

    This facility is often used to move the data and index files to a RAID or other fast solution, while retaining the main .frm files in the default data directory configured with the datadir option.

  • Limited number of ports

    Windows systems have about 4,000 ports available for client connections, and after a connection on a port closes, it takes two to four minutes before the port can be reused. In situations where clients connect to and disconnect from the server at a high rate, it is possible for all available ports to be used up before closed ports become available again. If this happens, the MySQL server appears to be unresponsive even though it is running. Ports may be used by other applications running on the machine as well, in which case the number of ports available to MySQL is lower.

    For more information about this problem, see;en-us;196271.

  • Concurrent reads

    MySQL depends on the pread() and pwrite() system calls to be able to mix INSERT and SELECT. We use mutexes to emulate pread() and pwrite(). We intend to replace the file level interface with a virtual interface in the future so that we can use the readfile()/writefile() interface to get more speed. The current implementation limits the number of open files that MySQL 5.1 can use to 2,048, which means that you cannot run as many concurrent threads on Windows as on Unix.

    This problem is fixed in MySQL 5.5.

  • Blocking read

    Before MySQL 5.1.41, MySQL uses a blocking read for each connection. That has the following implications if named-pipe connections are enabled:

    • A connection is not disconnected automatically after eight hours, as happens with the Unix version of MySQL.

    • If a connection hangs, it is not possible to break it without killing MySQL.

    • mysqladmin kill does not work on a sleeping connection.

    • mysqladmin shutdown cannot abort as long as there are sleeping connections.


    You cannot drop a database that is in use by another session.

  • Case-insensitive names

    File names are not case sensitive on Windows, so MySQL database and table names are also not case sensitive on Windows. The only restriction is that database and table names must be specified using the same case throughout a given statement. See Section 9.2.2, “Identifier Case Sensitivity”.

  • Directory and file names

    On Windows, MySQL Server supports only directory and file names that are compatible with the current ANSI code pages. For example, the following Japanese directory name will not work in the Western locale (code page 1252):


    The same limitation applies to directory and file names referred to in SQL statements, such as the data file path name in LOAD DATA INFILE.

  • The \ path name separator character

    Path name components in Windows are separated by the \ character, which is also the escape character in MySQL. If you are using LOAD DATA INFILE or SELECT ... INTO OUTFILE, use Unix-style file names with / characters:

    mysql> LOAD DATA INFILE 'C:/tmp/skr.txt' INTO TABLE skr;
    mysql> SELECT * INTO OUTFILE 'C:/tmp/skr.txt' FROM skr;

    Alternatively, you must double the \ character:

    mysql> LOAD DATA INFILE 'C:\\tmp\\skr.txt' INTO TABLE skr;
    mysql> SELECT * INTO OUTFILE 'C:\\tmp\\skr.txt' FROM skr;
  • Problems with pipes

    Pipes do not work reliably from the Windows command-line prompt. If the pipe includes the character ^Z / CHAR(24), Windows thinks that it has encountered end-of-file and aborts the program.

    This is mainly a problem when you try to apply a binary log as follows:

    C:\> mysqlbinlog binary_log_file | mysql --user=root

    If you have a problem applying the log and suspect that it is because of a ^Z / CHAR(24) character, you can use the following workaround:

    C:\> mysqlbinlog binary_log_file --result-file=/tmp/bin.sql
    C:\> mysql --user=root --execute "source /tmp/bin.sql"

    The latter command also can be used to reliably read in any SQL file that may contain binary data.

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