Reza, I can think of a KSDS that was being accessed by LSR, but every CI was touched until it was loaded into the LSR pool. Over 150 programs touched that 200 CYL baby in the same 60 minutes. Compression reduced the size by 55% reduced the IO by 55% as well.
In terms of IO savings it was the same as compressing a 30,000 (150x200) CYL file that is read once. My point: there is more to compression than just the size of the dataset. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > R Hey > Sent: Monday, February 22, 2010 9:23 PM > To: [email protected] > Subject: Re: [IBM-MAIN] SMS compression cost & size > > Thanks for the replies. > > Redbook on vsam says: > > There are some types of data sets that are not suitable for ZL compression, > resulting in rejection, such as these: > > - Small data sets. > - Data sets in which the pattern of the data does not produce a good > compression rate, such as image data. > - Small records. Compression is performed on a logical record basis. When > logical records are very short, the cost of additional work may become > excessive compared to the reduction in size that compression achieves. > > It seesm very complicated & book talks about: > > A compression-eligible data set can exist in one of three forms, depending on > the > moment: > > - Dictionary selection: ... > - Mated: The data set is mated with the appropriate dictionary; this concludes > the sampling and interrogation processes. > -Rejected: A suitable dictionary match was not found during sampling and > interrogation, so compression is bypassed, ... > > It has all sorts of don't & restrictions ... > I don't see why anyone would compress anything under 500 Cyl these days. > > Salute, > Rez > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: GET IBM-MAIN INFO > Search the archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
