How to measure and identify how much compression savings we are getting once we turn on the parm HISTORY-COMPRESSION=YES?

Document ID : KB000016743
Last Modified Date : 14/02/2018
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Question:

How to measure and identify how much compression savings we are getting once we turn on the parm HISTORY-COMPRESSION=YES? What is the average compression benefit we normally see ? Any ball park figure? 

 

Answer:

We do not have a benchmark on average overhead usage and space savings from using HISTORY-COMPRESSION=YES option. 

The history files will fill up quicker with compression turned off. The statistics file is low-volume, so the difference won't be noticeable. The accounting file however, is high-volume and will fill up quicker. 

HISTORY-COMPRESSION=[YES|NO] 

Specifies whether to compress the records that are written to the history data sets. CA SYSVIEW for DB2 uses hardware compression to compress history records, which generate little CPU overhead. The option can be turned on and off without reallocating the ACCT and STAT files. These files can have both uncompressed and compressed records mixed in the same file. 

Default: YES 

There are some statistics printed at data collector shutdown which will tell you about compression. Look for the following messages: 

DBG76005I DT32 11:57:02 33566 RECORDS WRITTEN ONTO OUTPUT FILE HSTSTATS. 

DBG76023I DT32 11:57:02 6 UNCOMPRESSED RECORDS WRITTEN TO FILE HSTSTATS 

DBG76024I DT32 11:57:02 69 MB OF DATA COMPRESSED FOR FILE HSTSTATS 

DBG76025I DT32 11:57:02 22 MB COMPRESSED DATA WRITTEN TO FILE HSTSTATS 

DBG76026I DT32 11:57:02 67 PERCENT COMPRESSION RATIO OBTAINED FOR FILE HSTSTATS 

DBG76027I DT32 11:57:02 000:00:00.152800 COMPRESSION TCB CPU USED FOR FILE HSTSTATS