APAR PI41677 zEDC support in Content Manager OnDemand for z/OS as updated by PI49323

Content

APARs PI41677 and PI49323 provide support to allow Content Manager OnDemand for z/OS (CMOD) to exploit the capability provided by zEnterprise Data Compression (zEDC) available with z/OS 2.1. The CMOD support utilizes the zEDC to perform compression and decompression for documents and resources stored with OD77 or OD77Lite compression. The zEDC can also be used by other CMOD functions that use OD77 or OD77Lite compression, such as ARSADMIN COMPRESS and DECOMPRESS.

In order to utilize zEDC hardware-based compression:

• The IFAPRDxx PARMLIB member must specify that the z/OS zEDC software feature is ENABLED;
• The RACF users for which use of the zEDC hardware is allowed must have READ access to FPZ.ACCELERATOR.COMPRESSION in the FACILITY CLASS; and
• Buffer sizes must meet the minimum sizes specified by the IQPPRMxx PARMLIB member. If the zEDC hardware cannot be used, software-based compression and decompression will be performed instead.

Two new compression types have been added to Content Manager OnDemand, named OD77HW and OD77LiteHW. In order to leverage hardware-based compression, you must define the document and resource compression types to one of these values. If hardware-based compression is not available, then OD77HW will default to OD77 (software-based) and OD77LiteHW will default to OD77Lite (software-based). For decompression, if hardware-based decompression is available, CMOD will always try to use it (even if the data was stored without OD77HW or OD77LiteHW). Note that OD77HW and OD77LiteHW use the exact same compression when they are able to use the zEDC; the difference between them is only when the zEDC is not available, in which case it defaults to the respective software-based compression algorithm.

Finally, the _HZC_COMPRESSION_METHOD=software environment variable can be used to force the zEDC to perform software-based compression and decompression.

By default, if there is a possibility that the compression can be run on the zEDC hardware, CMOD will use the zEDC. It is possible that once CMOD has invoked the zEDC, the zEDC may not let the operation run on the hardware. In that case, the zEDC will instead use software-based compression and decompression. This is done in a manner transparent to CMOD.

The OD77, OD77Lite, and zEDC (OD77HW and OD77LiteHW) compression types implement the same compression and decompression algorithm. That is, something compressed with one can be decompressed by the other. However, all three have been tuned differently, so that compressed sizes are different. The OD77 compression tends to compress better than the zEDC, which in turn tends to compresses better than OD77Lite. There is also a relationship between differences in compression and differences in CPU consumed, with greater compression consuming greater CPU. Experimentation should be performed with specific examples of data to determine what is the optimal compression type to use.

One of the impacts of different compressed sizes due to different algorithm tuning relates to the compressed resource objects. A resource compressed by zEDC will not be "equal" to the same resource compressed by OD77 or OD77Lite due to the different compressed sizes. This comparison difference can result in additional copies of resources being stored by ARSLOAD, increasing storage requirements. Evaluation of the impact should be performed prior to enabling zEDC usage by CMOD.

Content Manager OnDemand compression controls

In addition to the controls provided by the zEDC, CMOD provides a means of forcing the OD77 and OD77Lite software-based compression to be used instead of using the zEDC. If the ARS_USE_ZLIB_HW=0 environment variable is specified, the zEDC will not be used, and the OD77 or OD77Lite software-based compression will be used. The ARS_USE_ZLIB_HW=0 can be placed in the ARS.CFG file to affect all CMOD programs that process the ARS.CFG file.

Note that ARS_USE_ZLIB_HW=1 will not force the use of the zEDC hardware-based compression. The zEDC will ultimately determine if zEDC hardware-based or zEDC software-based compression will be used. ARS_USE_ZLIB_HW=1 (the default) merely allows CMOD to call the zEDC, which then decides to do software-based or hardware-based compression.

If finer granularity is required, two environment variables named ARS_ZLIB_HW_COMPRESS_BUF and ARS_ZLIB_HW_DECOMPRESS_BUF are provided. These values should match the zEDC values DEFMINREQSIZE parameter of IQPPRMxx and INFMINREQSIZE parameter of IQPPRMxx. The zEDC will only be invoked if the initial input buffer is greater than or equal to the specified size for the operation being performed. The defaults are ARS_ZLIB_HW_COMPRESS_BUF=4096 and ARS_ZLIB_HW_DECOMPRESS_BUF=16384.