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Extending Informix®Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix® includes many built-in extensions that are fully integrated in the database server. Informix® also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix®.
Creating extensionsYou can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
DataBlade® API Programmer's GuideThe Informix® DataBlade® API Programmer's Guide describes information about the DataBlade® API, the C-language application programming interface (API) provided with HCL Informix®.
Create user-defined routines
Manage memoryA C user-defined routine (UDR) has access to shared memory for dynamic allocations and stack memory for routine arguments (including the MI_FPARAM structure), local stack variables, and return values.
Shared memoryWhen a C UDR executes in a virtual processor (VP), it allocates memory from the shared memory of the database server.
Choose the memory duration
Public memory durationsThe DataBlade® API memory-management functions support several public memory durations. A UDR can use a public memory duration for most dynamic allocations of memory.
The PER_STMT_PREP memory durationA PER_STMT_PREP memory pool is associated with each SQL prepared statement. A prepared statement is an SQL statement that is parsed and ready for execution.

The PER_STMT_PREP memory duration

A PER_STMT_PREP memory pool is associated with each SQL prepared statement. A prepared statement is an SQL statement that is parsed and ready for execution.

The following table summarizes ways to create and drop a prepared statement.


Method	To create a prepared statement	To drop a prepared statement
Client application (SQL)	PREPARE	FREE
C UDR (DataBlade® API)	mi_prepare()	mi_drop_prepared_statement()

When a C UDR allocates PER_STMT_PREP memory, this memory is available to all routine instances that execute before the current prepared statement is dropped. Unlike PER_STMT_EXEC memory, PER_STMT_PREP memory does not get freed upon re-execution of the prepared statement; that is, it remains allocated if the cursor is closed and reopened. For example, in the second code fragment in Examples of using PER_STMT_EXEC memory duration, any PER_STMT_PREP memory that a_func() allocated is not released when the cursor is reopened. Therefore, any code that needs to access this memory once the cursor is reopened can do so. The PER_STMT_PREP memory that a_func() allocates remains allocated until the mi_drop_prepared_statement() drops the stmt prepared statement.

When the prepared SQL statement is dropped, the database server reclaims any PER_STMT_PREP memory in the memory context. It does not reclaim any memory in the memory context with a duration higher than PER_STMT_PREP.

No DataBlade API constructor function allocates its data type structure with a memory duration of PER_STMT_PREP.

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