The HPL data-unload process

The data-unload process is essentially the same as the load process, but in reverse. The data-unload process extracts the source data from one or more database tables; converts the data to a new format; and writes the converted data to a file, tape, or on UNIX™ to a pipe (application). As in a load, you can manipulate the data from a database table so that the converted data displays different characteristics.

The following figure shows how the components of the affect the data as it moves from a database to data files during the unload process. The HPL uses:
  • The query to select records from the database
  • The map to reorganize or modify the selected records
  • The format to prepare the records for writing out to the data files
  • The device array to find the location of the data files
Figure 1. The data-unload process
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The HPL uses the same components for an unload job as for a load job, with one exception. For an unload job, ipload creates a Structured Query Language (SQL) query that extracts selected data from the table. As with a load, unload components are grouped together into an unload job. Unload jobs can be saved, retrieved, and rerun as many times as necessary. Unload jobs can be grouped together with load jobs in the same project.