Advantages of using Datacom Presspack compression

Products

• Datacom
• IPC
• Datacom/AD
• Datacom/DB

Issue/Introduction

What are the advantages of using Datacom Presspack given that DASD is inexpensive?

Resolution

Even though DASD is an inexpensive cost, having Datacom data areas with significant compression can out perform the same data area uncompressed. The Datacom Multi-User (MUF) is a highly buffered system that works best when it can service data reads from existing buffers. The use of Datacom Presspack can greatly increase the number of data rows that can be stored in a data block and/or data buffer.

A compressed table will have more rows per buffer and the number of times a request can be serviced by a buffer read versus a DASD IO is improved. Every time a READ is performed from an buffer, there is a CPU saving since no IO issued, and no need to dump an existing buffer to load the new block.

The recommendation is to use compression when 40-50% of the average data footprint could be "saved". The more data compression that can be done, the more rows that fit per block/buffer = the more CPU savings to balance the extra DASD cost against the extra CPU to compress/decompress.

Additional Information

Another option to save cost is to convert existing Datacom areas from using BDAM to Linear VSAM access method. Linear VSAM runs under IBM zIIP CPU's and can increases overall CPU throughput at lower operational costs.