ST_Geometry functions in Oracle and PostgreSQL are implemented in structured query language (SQL). This is a database-level language. In Oracle, it is Procedural Language Structured Query Language (PL/SQL). In PostgreSQL, it is PL/pgSQL.
When you access ST_Geometry columns in an Oracle or PostgreSQL database using SQL functions, you are accessing the database directly; therefore, the database must be able to access the ST_Geometry functions. In Oracle, the database also spawns an extproc process.
In SQLite, ST_Geometry functions are implemented in C in the ST_Geometry library. You must access the ST_Geometry library to use the ST_Geometry functions.
The st_geometry library must be stored in the PostgreSQL installation directory to allow PostgreSQL to access the ST_Geometry functions. You must copy the st_geometry.dll (Windows) file to the lib folder in the PostgreSQL installation directory. For Linux servers, copy the st_geometry.so (Linux) file to the /usr/lib/pgsql directory on the PostgreSQL server. Both of these files can be found in the DatabaseSupport folder of your ArcGIS client installation.
Functions are implemented in PL/SQL, which calls functions in external shared library files written in the C programming language. The functions are called from PL/SQL using an alias name that maps the name of the library—in the case of ST_Geometry in Oracle, ST_SHAPELIB—to the name of the library file. (See the documentation for the Oracle CREATE LIBRARY command for details.) The first time a spatial type function is called that requires ST_SHAPELIB, the database requests the listener to spawn an extproc process for the SQL session. The extproc is given the location of ST_SHAPELIB, the name of the function to be called, and its parameters. The extproc loads ST_SHAPELIB and calls the function. When the external function completes, the extproc returns the results and remains active, waiting for additional function calls during this session. The extproc process terminates when the SQL session disconnects.
To make this work, the following configuration is needed:
- The database needs to know the location of the file containing ST_SHAPELIB so it can pass this information to the listener process and on to the extproc.
- If the file_spec for the ST_SHAPELIB in the user_libraries table does not match the physical file location of the ST_SHAPELIB on the server, ST_Geometry operators and functions will not work. Therefore, you must update the library definition in the Oracle user libraries to include the correct library path to the file containing ST_SHAPELIB using the CREATE LIBRARY command.
- The database must know of the service that handles requests to the extproc. This is configured in the file tnsnames.ora.
- The extproc must be allowed to load the file containing ST_SHAPELIB. This is done by defining the environment variable EXTPROC_DLLS in the listener.ora file (Oracle 10g) or extproc.ora file (Oracle 11g).
- The extproc (usually running as the user who owns ORACLE_HOME) must have read permissions on the location of the library files and execute permissions on the files.
- If you alter the listener.ora file, you must restart the listener.
You must designate the location of and load the ST_Geometry library so the SQLite client can access the SQL functions. You can set the library location in the client's PATH (Windows) or LIBPATH (Linux) system environment variable then load the library, or you can specify the path when you load ST_Geometry library. See Load the SQLite ST_Geometry library for instructions.