The LONG VARCHAR and LONG VARGRAPHIC data types have a limit of 32K bytes of storage. While this may be sufficient for small to medium size text data, applications often need to store large text documents. They may also need to store a wide variety of additional data types such as audio, video, drawings, mixed text and graphics, and images. DB2 provides three data types to store these data objects as strings of up to two (2) gigabytes (GB) in size. The three data types are: Binary Large Objects (BLOBs), single-byte Character Large Objects (CLOBs), and Double-Byte Character Large Objects (DBCLOBs).
Along with storing large objects (LOBs), a way is also needed to refer to, and to use and modify, each LOB in the database. Each DB2 table may have a large amount of associated LOB data. Although any single LOB value may not exceed 2 gigabytes, a single row may contain as much as 24 gigabytes of LOB data, and a table may contain as much as 4 terabytes of LOB data. The content of the LOB column of a particular row at any point in time has a large object value.
You can refer to and manipulate LOBs using host variables just as you would any other data type. However, host variables use the client memory buffer which may not be large enough to hold LOB values. Other means are necessary to manipulate these large values. Locators are useful to identify and manipulate a large object value at the database server and for extracting pieces of the LOB value. File reference variables are useful for physically moving a large object value (or a large part of it) to and from the client.
| Note: | DB2 offers LOB support for JDBC and SQLJ applications. For more information on using LOBs in Java applications, see JDBC 2.0. |
The subsections that follow discuss in more detail those topics introduced above.