Reporting and Logging › Compression Analysis Utility TBECMPCA › How the TBECMPCA Utility Processes Files for Analysis

How the TBECMPCA Utility Processes Files for Analysis

TBECMPCA attempts to mimic CA Tape Encryption processing as much as possible, so it does not process block less than 1024 bytes and stops after processing 24 MB which is where the first test for minimum compression rate is checked. If you use the READTOEOF to process more than 24 MB, TBECMPCA can not mimic the realtime process of skipping compression when the minimum compression rate is not met. This means an analysis of an entire file may not match the result from the realtime process. CA Tape Encryption processes data at a channel command level. This normally results in data being processed in buffers equal to the block size of the file. The TBECMPCA compression analysis utility attempts to reproduce this by reading the input one block at a time. This provides better compression rates and faster times than reading record by record.

The compression analysis utility reads the SYSUT1 data one time. After each block is read, the block is compressed and then expanded by each method. The next block is read until the 24 MB or the STOPAFTER value is reached. The run time of the compression analysis utility does not necessarily reflect the run time of your programs with the same input file, because of the way programs access data differently. You can determine how much of the run time of the compression analysis utility is not related to compression or expansion routines by specifying PARM=NOCOMP. This bypasses the code between the TTIMER macros.

It is possible that your run time may not be extended by the full time that the compression analysis report shows for a compression method. This is because CA Tape Encryption will be compressing or expanding the data during the time your program is performing I/O. If you program overlaps processing with that I/O, you might only see a portion of the compression time.