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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®.
Descriptor function referenceThese topics provide the syntax and usage for the functions that the HCL Informix® database server supplies to access-method developers.
Accessor functionsThe Virtual-Table Interface (VTI) library contains functions that primarily access selected fields from the various descriptors.
The mi_scan_isolevel() accessor functionThe mi_scan_isolevel() function retrieves the isolation level that the database server expects for the table that am_getnext scans.

The mi_scan_isolevel() accessor function

The mi_scan_isolevel() function retrieves the isolation level that the database server expects for the table that am_getnext scans.

Syntax

MI_ISOLATION_LEVEL mi_scan_isolevel(MI_AM_SCAN_DESC *scanDesc);

scanDesc: Points to the scan descriptor.

Usage

If the access method supports isolation levels, it can call mi_scan_isolevel() from am_beginscan to determine the correct isolation level.

Call mi_scan_isolevel() to validate that the isolation level requested by the application does not surpass the isolation level that the access method supports. If the access method supports Serializable, it does not call mi_scan_isolevel() because Serializable includes the capabilities of all the other levels.

Return values

MI_ISO_NOTRANSACTION: Indicates that no transaction is in progress.
MI_ISO_READUNCOMMITTED: Indicates Dirty Read.
MI_ISO_READCOMMITTED: Indicates Read Committed.
MI_ISO_CURSORSTABILITY: Indicates Cursor Stability.
MI_ISO_REPEATABLEREAD: Indicates Repeatable Read.
MI_ISO_SERIALIZABLE: Indicates Serializable.

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