Large object management

The Large Object Locator extension enables you to create a single consistent interface to large objects. It extends the concept of large objects to include data stored outside the database.

stores large object data (data that exceeds a length of 255 bytes or contains non-ASCII characters) in columns in the database. You can access this data using standard SQL statements. The server also provides functions for copying data between large object columns and files. See Informix® Guide to SQL: Syntax and Informix® Guide to SQL: Tutorial for more information.

With Large Object Locator you create a reference to a large object and store the reference as a row in the database. The object itself can reside outside the database: for example, on a file system (or it could be a BLOB or CLOB type column in the database). The reference identifies the type, or access protocol, of the object and points to its storage location. For example, you could identify an object as a file and provide a path name to it or identify it as a binary or character smart large object stored in the database. Smart large objects are a category of large objects that include CLOB and BLOB data types, which store text and images. Smart large objects are stored and retrieved in pieces, and have database properties such as crash recovery and transaction rollback.

You access a large object by passing its reference to a Large Object Locator function. For example, to open a large object for reading or writing, you pass the object's reference to the lld_open() function. This function uses the reference to find the location of the object and to identify its type. Based on the type, it calls the appropriate underlying function to open the object. For example, if the object is stored on a UNIX™ file system, lld_open() calls a UNIX™ function to open the object.
Important: In theory, you could use Large Object Locator to reference any type of large object in any storage location. In practice, access protocols must be built into Large Object Locator for each type of supported object. Because support for new types can be added at any time, be sure to read the release notes accompanying this publication-not the publication itself-to see the types of large objects Large Object Locator currently supports.