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27.3.4.5. Compiling and Installing User-Defined Functions

Files implementing UDFs must be compiled and installed on the host where the server runs. This process is described below for the example UDF file sql/udf_example.cc that is included in the MySQL source distribution.

The immediately following instructions are for Unix. Instructions for Windows are given later in this section.

The udf_example.cc file contains the following functions:

  • metaphon() returns a metaphon string of the string argument. This is something like a soundex string, but it's more tuned for English.

  • myfunc_double() returns the sum of the ASCII values of the characters in its arguments, divided by the sum of the length of its arguments.

  • myfunc_int() returns the sum of the length of its arguments.

  • sequence([const int]) returns a sequence starting from the given number or 1 if no number has been given.

  • lookup() returns the IP number for a hostname.

  • reverse_lookup() returns the hostname for an IP number. The function may be called either with a single string argument of the form 'xxx.xxx.xxx.xxx' or with four numbers.

A dynamically loadable file should be compiled as a sharable object file, using a command something like this:

shell> gcc -shared -o udf_example.so udf_example.cc

If you are using gcc, you should be able to create udf_example.so with a simpler command:

shell> make udf_example.so

You can easily determine the correct compiler options for your system by running this command in the sql directory of your MySQL source tree:

shell> make udf_example.o

You should run a compile command similar to the one that make displays, except that you should remove the -c option near the end of the line and add -o udf_example.so to the end of the line. (On some systems, you may need to leave the -c on the command.)

After you compile a shared object containing UDFs, you must install it and tell MySQL about it. Compiling a shared object from udf_example.cc produces a file named something like udf_example.so (the exact name may vary from platform to platform). Copy this file to the server's plugin directory. This directory is given by the value of the plugin_dir system variable. (Note: This a change in MySQL 5.1. For earlier versions of MySQL, the shared object can be located in any directory that is searched by your system's dynamic linker.)

On some systems, the ldconfig program that configures the dynamic linker does not recognize a shared object unless its name begins with lib. In this case you should rename a file such as udf_example.so to libudf_example.so.

On Windows, you can compile user-defined functions by using the following procedure:

  1. You need to obtain the BitKeeper source repository for MySQL 5.1. See Section 2.8.3, “Installing from the Development Source Tree”.

  2. In the source repository, look in the VC++Files/examples/udf_example directory. There are files named udf_example.def, udf_example.dsp, and udf_example.dsw there.

  3. In the source repository, look in the sql directory. Copy the udf_example.cc from this directory to the VC++Files/examples/udf_example directory and rename the file to udf_example.cpp.

  4. Open the udf_example.dsw file with Visual Studio VC++ and use it to compile the UDFs as a normal project.

After the shared object file has been installed, notify mysqld about the new functions with these statements:

mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME 'udf_example.so';
mysql> CREATE FUNCTION myfunc_double RETURNS REAL SONAME 'udf_example.so';
mysql> CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME 'udf_example.so';
mysql> CREATE FUNCTION lookup RETURNS STRING SONAME 'udf_example.so';
mysql> CREATE FUNCTION reverse_lookup
    ->        RETURNS STRING SONAME 'udf_example.so';
mysql> CREATE AGGREGATE FUNCTION avgcost
    ->        RETURNS REAL SONAME 'udf_example.so';

Functions can be deleted using DROP FUNCTION:

mysql> DROP FUNCTION metaphon;
mysql> DROP FUNCTION myfunc_double;
mysql> DROP FUNCTION myfunc_int;
mysql> DROP FUNCTION lookup;
mysql> DROP FUNCTION reverse_lookup;
mysql> DROP FUNCTION avgcost;

The CREATE FUNCTION and DROP FUNCTION statements update the func system table in the mysql database. The function's name, type and shared library name are saved in the table. You must have the INSERT and DELETE privileges for the mysql database to create and drop functions.

You should not use CREATE FUNCTION to add a function that has previously been created. If you need to reinstall a function, you should remove it with DROP FUNCTION and then reinstall it with CREATE FUNCTION. You would need to do this, for example, if you recompile a new version of your function, so that mysqld gets the new version. Otherwise, the server continues to use the old version.

An active function is one that has been loaded with CREATE FUNCTION and not removed with DROP FUNCTION. All active functions are reloaded each time the server starts, unless you start mysqld with the --skip-grant-tables option. In this case, UDF initialization is skipped and UDFs are unavailable.


 
 
  Published under the terms of the GNU General Public License Design by Interspire