LOAD provides the functions UNLOAD and RELOAD as well as SAVE and RESTORE for any number of users. Tables which temporarily are not needed can be unloaded from the database using UNLOAD to make space; they can be reloaded into the database using RELOAD. The functions SAVE and RESTORE generate backup versions of a table which can be loaded again; e.g., after an application program has run.
TABLEEXTRACT, TABLEUNLOAD, and TABLELOAD complete CATALOGEXTRACT and CATALOGLOAD and transfer the contents of database tables as well as LONG columns and indexes.
TABLEEXTRACT performs the function SAVE which backs up the database without modifying it. If temporary space is needed in the database, the statement TABLEUNLOAD can be used instead of TABLEEXTRACT. TABLEUNLOAD unloads tables; i.e., the contents of the tables are deleted and operations on these tables are not possible until they have been reloaded using TABLELOAD.
With TABLELOAD, the data can be loaded whether it is still available in the database (after TABLEEXTRACT) or not (after TABLEUNLOAD). This means, this command performs the functions RELOAD and RESTORE as well.
Only the data pages are saved. Information about the catalog is managed by LOAD. Thus the scope of table definitions regarded as compatible with this data is relatively large:
- It is not necessary to reload the data either into the same table or into a table having the same definition as the original table. Table and column names are not important for deciding whether the file and the target table are compatible with each other. Certain structural differences may be adapted by LOAD. In such a case, the target table will be modified so that its structure fits the file's data.
- Database contents can be transferred from one computer to another. The necessary conversions are made in the process.
- If the database contains unused pages, it can be reduced. To do so, all the data must be unloaded. Afterwards, the database must be reconfigured with smaller devspaces and the data must then be reloaded.
As for the CATALOG EXTRACT/LOAD statements, there are the three options ALL, USER, and TABLE.
The option ALL is only accepted for a user with SYSDBA status. Only the datasets residing on this location are extracted and only tables stored on this location can be reloaded.
Controlled by the options USER and TABLE, normal users can unload and reload all or particular base tables belonging to them.
The referenced statements may be part of a command file and may be executed in batch.