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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.
Virtual-Table Interface GuideThe 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®.
Purpose-function referenceThese topics describe the purpose functions that the access-method developer provides.
Purpose-function syntaxThe database server expects a particular prototype for each purpose function. As the access-method developer, you program the actions of a purpose function but must use the parameters and return values that the Virtual-Table Interface (VTI) prototypes specify.
The am_stats purpose functionThe database server calls am_stats to process an UPDATE STATISTICS statement.

The am_stats purpose function

The database server calls am_stats to process an UPDATE STATISTICS statement.

Syntax

mi_integer am_stats(MI_AM_TABLE_DESC *tableDesc,
   MI_AM_TSTATS_DESC *tstatsDesc);

tableDesc: Points to the table descriptor.
tstatsDesc: Points to the statistics descriptor.

Usage

To influence the am_stats sampling rate, an UPDATE STATISTICS statement might include an optional distribution-level keyword, low, medium, or high. If the UPDATE STATISTICS statement does not include one of these keywords, the default low distribution level applies.

Adjust the sampling rate in your version of the am_stats purpose function according to the distribution-level keyword that the user specifies in the UPDATE STATISTICS statement. To determine which keyword-LOW, MEDIUM, or HIGH-an UPDATE STATISTICS statement specifies, call the mi_tab_update_stat_mode() function.

The am_stats purpose function calls the various Virtual-Table Interface (VTI) accessor functions that set values in the statistics descriptor for the database server. The database server places the statistics descriptor results in the systables and syscolumns, system catalog tables. The am_stats function can also save any additional values in a location that am_scancost can access, such as a file in the extspace or a table in sbspace.

Return values

MI_OK: Indicates success.
MI_ERROR: Indicates failure.

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