Using Extended Compression

TCP/IP connections accommodate greater bandwidth to transfer large files than older technologies eliminating the need to compress data. Data can be sent in its original state saving both time and the need to decompress data once it has been transferred. However, if you have a slow line and high CPU capacity, compression may be warranted. Under other conditions, compression consumes a lot of CPU and slows transfer rates considerably while giving little if any return given the cost of CPU time.

Different Methods of Using Extended Compression

You can compress and store files in ZLIB-compressed format using one of the following methods:

  • On a global basis using the Extended Compression (ECZ) initialization parameters. If you always transfer the same type of data, you may benefit by changing the global default values of the extended compression initialization parameters.
  • On a Process basis using the EXT parameters in the COPY statement. If you send a variety of data types, it is probably more efficient to retain the default values of the initialization parameters and override them on a Process-by-Process basis using the COPY statement. For information on overriding the extended compression parameters in the COPY statement, see the Connect:Direct Process Language help.
  • Through the DGASACMP batch utility. This option allows the CPU consumption, or overhead of extended compression, to be offloaded from IBM® Connect:Direct® to the standalone utility. The CPU time consumed by this utility can be much greater than that consumed by IBM Connect:Direct because the DGASACMP utility must use record mode compression whereas IBM Connect:Direct can use block mode compression. You can also use the DGASACMP batch utility to decompress the data and store it in its original format on the remote node where compressed data has been sent. The DGASACMP utility produces a report, which shows how much the data was read, written, compressed, and how long it took to compress so you can determine the benefits of changing the default values of the extended compression parameters.

Changing the Values of ECZ Parameters

The effects of changing the default values for the ECZ.COMPRESSION.LEVEL, ECZ.MEMORY.LEVEL, and ECZ.WINDOWSIZE extended compression parameters are not always predictable and can significantly increase CPU utilization. The default values for the three parameters produce very good results for a wide variety of data types. Typically, it is only beneficial to change these default values if line speeds are limited, data is repetitive, and CPU is available.