Performance considerations for the XBLKS installation option

Transfer blocks (XBLKs) perform the following functions in the PRELOAD phase or the COMBINED phase of LOADPLUS:

  • Moving data from the read task to the sort/data task
  • Moving non-data-sorting index records from the sort/data task to the probe or index task

Related topic

Additional-performance-information-for-LOADPLUS-installation-and-command-options

The read task reads data from SYSREC, completes all conditional processing, and moves the row image into an XBLK. If multiple sort/data tasks exist, an XBLK is associated with each task. When an XBLK is full, it becomes available for processing by the sort/data task.

The sort/data processes pass information to the probe or index task by using one or more XBLKs. The probe task is used when checking referential constraints. The index task is used when an additional sort process is necessary to check for duplicate keys.

The number of XBLKS that LOADPLUS allocates is a function of the number of read, sort/data probe, and index tasks that are active for a particular LOADPLUS job. The XBLKS installation option specifies how many XBLKs to allocate per receiving the task. The minimum value for the XBLKS option is 3, which is the value that is shipped with LOADPLUS. A larger number can marginally improve performance, but can also increase paging. XBLKs are 64 KB each and are allocated from storage below the bar.

 

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