Built-in Access Methods

An access method consists of software routines that open files, retrieve data into memory, and write data to permanent storage such as a disk.

A primary access method provides a relational-table interface for direct read and write access. A primary access method reads directly from and writes directly to source data. It provides a means to combine data from multiple sources in a common relational format that the database server, users, and application software can use.

A secondary access method provides a means to index data for alternate or accelerated access. An index consists of entries, each of which contains one or more key values and a pointer to the row in a table that contains the corresponding value or values. The secondary access method maintains the index to coincide with inserts, deletes, and updates to the primary data.

Dynamic Server recognizes both built-in and user-defined access methods. Although an index typically points to table rows, an index can point to values within smart large objects or to records from external data sources.

The database server provides the following built-in access methods:

• The built-in primary access method scans, retrieves, and alters rows in IBM Informix relational tables.

  By default, tables that you create with the CREATE TABLE statement use the built-in primary access method.

• The built-in secondary access method is a generic B-tree index.

  By default, indexes that you create with the CREATE INDEX statement use this built-in secondary access method. For more information about the built-in B-tree index, refer to the IBM Informix: Guide to SQL Syntax.