Home
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 extensions
You 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 Guide
The 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 memory
A 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 memory
When 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 durations
The 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_EXEC memory duration
A PER_STMT_EXEC memory pool is associated with the execution of each SQL statement. A statement is the entire SQL statement plus any SQL commands that the SQL statement initiates.
Uses of PER_STMT_EXEC memory duration
The PER_STMT_EXEC memory duration is useful for communications between UDRs, parallel execution, user-defined aggregates, and named memory, and for memory allocations within an end-of-statement callback (if you have information to pass to the callback).

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.
- Informix® extensions and DataBlade® modules
  These topics describe how to use built-in database extensions and separately installed DataBlade® modules.
- Creating extensions
  You 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 Guide
    The Informix® DataBlade® API Programmer's Guide describes information about the DataBlade API, the C-language application programming interface (API) provided with HCL Informix.
    - DataBlade® API overview
    - Data manipulation
    - Database access
    - Create user-defined routines
      - Develop a user-defined routine
        A C user-defined routine (UDR) is a UDR that is written in the C language and uses the server-side implementation of the DataBlade® API to communicate with the database server. C UDRs (functions and procedures) are implemented as C-language functions. DataBlade modules often include C UDRs that are made available for use by registering them in the database.
      - Write a user-defined routine
        This section outlines some implementation issues for C user-defined routines (UDRs). This section also describes the specific features and tasks of a C UDR.
      - Manage memory
        A 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 memory
        When a C UDR executes in a virtual processor (VP), it allocates memory from the shared memory of the database server.
        Access shared memory
        A C UDR executes in a virtual processor, which is associated with an operating-system process. While a C UDR executes on a VP (VP #1), it can access memory that is associated with that virtual processor. This memory space includes the stack, heap, and data segments of the VP.
        Choose the memory duration
        Public memory durations
        The 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_ROUTINE memory duration
        A PER_ROUTINE memory pool is associated with each routine invocation. A routine invocation is one single execution of a UDR within a routine instance.
        The PER_COMMAND memory duration
        A PER_COMMAND memory pool is associated with each SQL command. An SQL command is a subquery, which is a separate SQL statement initiated as part of the current SQL statement. The most common kind of subquery is a SELECT statement in the WHERE clause of a SELECT.
        The PER_STATEMENT memory duration
        A PER_STATEMENT memory pool can be associated with each SQL statement, until execution of the statement is complete and for a prepared statement, until the statement terminates. The statement includes any SQL commands that the SQL statement initiates.
        The PER_STMT_EXEC memory duration
        A PER_STMT_EXEC memory pool is associated with the execution of each SQL statement. A statement is the entire SQL statement plus any SQL commands that the SQL statement initiates.
        Examples of using PER_STMT_EXEC memory duration
        Uses of PER_STMT_EXEC memory duration
        The PER_STMT_EXEC memory duration is useful for communications between UDRs, parallel execution, user-defined aggregates, and named memory, and for memory allocations within an end-of-statement callback (if you have information to pass to the callback).
        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.
        Advanced memory durations
        Memory-duration considerations
        Manage shared memory
        Manage stack space
        Session threads execute C UDRs and their thread-stack space is allocated from a common region in shared memory. The thread stack stores nonshared data for the UDRs and system routines that the thread executes. This stack contains everything that would normally be on the execution stack, including routine arguments (including the MI_FPARAM structure, local (stack) variables, and function return values.
      - Create special-purpose UDRs
        This section describes how to create special UDRs, such as iterator functions, user-defined aggregates, and optimization functions.
      - Extend data types
        This section describes the ways to extend data types with C user-defined routines (UDRs).
    - Appendix
      This section contains additional reference information.
  - DataBlade® API Function Reference
    The Informix® DataBlade® API Function Reference describes the DataBlade API functions and the subset of Informix ESQL/C functions that the DataBlade API supports.
  - DataBlade® Developers Kit
    The DataBlade® Developers Kit (DBDK) guides contain information about the tools you can use to develop and package DataBlade modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The J/Foundation Developer's Guide describes how to write user-defined routines (UDRs) in the Java™ programming language for Informix®.
  - R-Tree Index User's Guide
    The Informix® R-Tree Index User's Guide describes the HCL Informix R-tree secondary access method and how to access and use its components.
  - User-Defined Routines and Data Types Developer's Guide
    The Informix® User-Defined Routines and Data Types Developer's Guide describes how to define new data types and enable user-defined routines (UDRs) to extend HCL Informix.
  - Virtual-Table Interface Guide
    The Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix tables and to data that does not conform to the storage scheme of HCL Informix.
  - Virtual-Index Interface Guide
    The Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix typically with a DataBlade® module.

Uses of PER_STMT_EXEC memory duration

The PER_STMT_EXEC memory duration is useful for communications between UDRs, parallel execution, user-defined aggregates, and named memory, and for memory allocations within an end-of-statement callback (if you have information to pass to the callback).

Important: Any memory with a duration higher than PER_COMMAND can have multiple threads access it. Consider whether you need to handle concurrency issues for any PER_STMT_EXEC memory you allocate. For more information, see Handling concurrency issues.

Several DataBlade® API constructor functions allocate their DataBlade® API data type structure with a PER_STMT_EXEC memory duration. The following table lists DataBlade® API data type structures that have a memory duration of PER_STMT_EXEC.

Table 1. DataBlade® API data type structures with a PER_STMT_EXEC memory duration
DataBlade® API data type structure	DataBlade® API constructor function	DataBlade® API destructor function
Connection descriptor (MI_CONNECTION)	mi_open()	mi_close()
Save-set structure (MI_SAVE_SET)	mi_save_set_create()	mi_save_set_destroy()

Switching the current memory duration before one of the constructor functions in DataBlade API data type structures with a PER_STMT_EXEC memory duration does not change the PER_STMT_EXEC memory duration of the allocated DataBlade® API structure. These data type structures are freed by their destructor function or when execution of the current SQL statement completes. To retain access to some of these DataBlade® API data type structures after the statement completes, you must save them at the per-session level.

Tip: The DataBlade® API supports the ability to save information at a per-session level. This ability, however, is an advanced feature of the DataBlade® API. For more information, see Obtain a session-duration connection descriptor.