Automatic Compression of the Global Library

Because of its PDS (partitioned dataset) organization, the global library is prone to D37 abends (insufficient space to write to disk). If, at your site, there is no product to keep the library compressed, Control‑O enables you to automatically compress the global library whenever it becomes full, as explained below.

The Automatic Compression facility is normally activated when the global library is full (that is, when a D37 abend is encountered during a WRITEGLOBAL operation).

Before attempting to compress the global library, Control‑O backs up the library to a sequential file using utility IEBCOPY. The name of the backup sequential file is the name of the specified global library with the suffix ".COPY". For example, when global library CTO.Vxxx.GLB.CPUSYSA is backed up, the resulting sequential file name is: CTO.Vxxx.GLB.CPUSYSA.COPY

The backup sequential file is allocated only if parameter GLBCOMP in member CTOPARM is set to Y (Yes), indicating that the global compress feature is required.

The Automatic Compression facility uses member $$COMPST of the global library to track the progress of the compression operation. $$COMPST is a single record member that is created automatically when the global library is defined.

For each step in the backup and compression process, variable %%STATUS in member $$COMPST is updated to reflect the status of the compression process. The following table lists the possible values for this variable:

Table 195 Values for Variable $$COMPST

Whenever the global library is accessed (using a LOADGLOBAL or WRITEGLOBAL operation), the value of %%STATUS is checked to ensure that the library was not corrupted during the last automatic compress operation.

• If the value of %%STATUS is OK, the requested LOADGLOBAL or WRITEGLOBAL operation is performed.
• If the value of %%STATUS is S2, the Automatic Compression facility automatically restores the global library from the backup file and compresses it before execution of the LOADGLOBAL or WRITEGLOBAL operation.
• If the value of %%STATUS is S1, the global library and backup may be corrupt, and therefore the operation cannot be performed. An error message is issued.