Welcome
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 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.
Virtual-Index Interface Guide
The IBM® 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 module.
Descriptor function reference
Descriptors
Statistics descriptor
An access method returns statistics to the UPDATE STATISTICS statement in a statistics descriptor, or MI_AM_ISTATS_DESC structure. The database server copies the separate values from the statistics descriptor to pertinent tables in the system catalog.

HCL Informix® V15.0.0 documentation
Welcome to the documentation for HCL Informix® 15.0.0 and related client tools and products.
Product overview
HCL Informix® is a fast and scalable database server that manages traditional relational, object-relational, and dimensional databases. Its small footprint and self-managing capabilities are suited to embedded data-management solutions.
Installing
These topics describe how to install HCL Informix® database servers, client products, and modules.
Administering
In addition to administering the database server, you can tune performance, replicate data, and archive data.
Migrating and upgrading
You can upgrade to the 15.0.0 release of HCL Informix® or migrate from other database servers to Informix. Upgrading is an in-place migration method that uses your existing hardware and operating system software. Some changes to the Informix database server can affect upgrading from a previous release.
Client APIs and tools
You can use the HCL Informix® implementation of client APIs to develop applications for Informix database servers.
Embedding Informix®
When you embed HCL Informix®, you can use enterprise-class high-availability and high performance with embeddability features such as easy programmability, a small disk and memory footprint, and silent deployment.
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 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 modules
  These topics describe how to use built-in database extensions and separately installed 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.
  - Programmer's Guide
    The HCL® Informix® DataBlade® API Programmer's Guide describes information about the , the C-language application programming interface (API) provided with HCL Informix.
  - Function Reference
    The IBM® Informix® DataBlade® API Function Reference describes the functions and the subset of functions that the supports.
  - Developers Kit
    The Developers Kit (DBDK) guides contain information about the tools you can use to develop and package modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The HCL® 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 HCL® 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 HCL® 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 IBM® 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 IBM® 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 module.
    - Access methods
      This section describes access methods, explains why you create user-defined access methods, and shows you how to create user-defined access methods
    - Develop an access method
      These topics describe the steps that you take to implement a user-defined access method with the Virtual-Index Interface (VII).
    - Design decisions
      These topics present the choices that you make to optimize the performance and flexibility of the access method that you can create with the virtual-index interface (VII).
    - Purpose-function reference
      These topics describe the purpose functions that the access-method developer provides.
    - Descriptor function reference
      - Descriptors
        Key descriptor
        The key descriptor, or MI_AM_KEY_DESC structure, identifies the keys and operator class for an index.
        Qualification descriptor
        A qualification descriptor, or MI_AM_QUAL_DESC structure, describes the conditions in the WHERE clause of an SQL statement.
        Row descriptor
        A row descriptor, or MI_ROW_DESC structure, typically describes the columns that the CREATE INDEX statement establishes for an index. A row descriptor can also describe a single row-type column.
        Row-ID descriptor
        Scan descriptor
        The scan descriptor, or MI_AM_SCAN_DESC structure, contains the specifications of an SQL query
        Statistics descriptor
        An access method returns statistics to the UPDATE STATISTICS statement in a statistics descriptor, or MI_AM_ISTATS_DESC structure. The database server copies the separate values from the statistics descriptor to pertinent tables in the system catalog.
        Table descriptor
        The table descriptor, or MI_AM_TABLE_DESC structure, provides information about the index, particularly the data definition from the CREATE INDEX statement that created the object.
        Files to include in the access-method build
        The access method must include header files with descriptor and function declarations.
      - Accessor functions
        The Virtual-Index Interface (VII) library contains functions that primarily access selected fields from the various descriptors.
    - SQL statements for access methods
      These topics describe the syntax and usage of the ALTER ACCESS_METHOD, CREATE SECONDARY ACCESS_METHOD, and DROP ACCESS_METHOD statements, which insert, change, or delete entries in the sysams system catalog table.
    - XA-compliant external data sources
      The HCL Informix® Transaction Manager recognizes XA-compliant external data sources, which can participate in two-phase commit transactions.
Data warehousing
In addition to designing and implementing Informix® dimensional databases, you can use tools to create data warehouse applications and optimize your data warehouse queries.
Designing databases
The first step in creating a relational database is to construct a data model, which is a precise, complete definition of the data you want to store. After you prepare your data model, you must implement it as a database and tables. To implement your data model, you first select a data type for each column and then you create a database and tables and populate the tables with data. You can also implement fragmentation strategies and control access to your data.
JSON compatibility
You can use the popular JSON-oriented query language created by MongoDB to interact with data stored in HCL Informix®.
Security
You can secure your Informix® database server and the data that is stored in your Informix databases. You can encrypt data, secure connections, control user privileges and access, and audit data security.
SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
Troubleshooting HCL Informix®
Several troubleshooting techniques, tools, and resources are available for resolving problems that you encounter in your HCL Informix® database server environment.

Statistics descriptor

An access method returns statistics to the UPDATE STATISTICS statement in a statistics descriptor, or MI_AM_ISTATS_DESC structure. The database server copies the separate values from the statistics descriptor to pertinent tables in the system catalog.

The following accessor functions set information in the statistics descriptor.


Accessor function	Value set
mi_istats_set2lval()	A pointer to the second largest key value in the index
mi_istats_set2sval()	A pointer to the second smallest key value in the index
mi_istats_setclust()	The degree of clustering A low number indicates fewer clusters and a high degree of clustering.
mi_istats_setnleaves()	The number of leaves in the index
mi_istats_setnlevels()	The number of levels in the index
mi_istats_setnunique()	The number of unique keys in the index