Unloads

Figure 6 shows the onpload unload process. In the unload process, the behavior of onpload parallels the behavior described in Threads That the onpload Utility Uses and Threads That the Database Server Uses, except that the threads are unloading the data instead of loading it.

Figure 6. The Unload Procedure

The ulstrm (unload-stream) thread packages data for output to the onpload client from the query plan. The SQL optimizer creates the query plan. The query plan behaves like a query plan running from any other client, such as DB–Access. The exchange operator distributes the resulting data to the ulworker threads in a round-robin fashion, and onpload unloads the data onto tapes or files.

Parallelism with respect to the output device, the source table fragments, and the flow of the data is evident in Figure 6.