The performance issue that I remember had to do with any software product that creates a large number of dynamic allocations. Each such allocation requires a new entry in the TIOT for the DDNAME. One example of such a product is DB2. Periodically SMF records may be written to record the cumulative EXCP counts for each DDNAME currently allocated. This is done in order to be able to account for I/O requests from a never-ending job, like DB2. The original implementation of SMF only recorded EXCP counts when the file was closed, which will never happen if the job never ends. A later version of SMF added interval accounting records so that most of the I/O load could be accounted for in the event that the file was never closed properly. If the number of DD statements is exceptionally huge, it was found to be taking a very long time with lots of CPU overhead to consolidate all these DD statements before writing the SMF records. Certain new options were made available to giv! e the installation more control over this overhead. Barry Merrill can give all the sordid details.
The real cause of the performance problem was not moving the TIOT above the 31-bit addressing line but rather having an enormous number of DD statements allocated that are manipulated by SMF at the end of each SMF recording interval, regardless of where the TIOT resides. Moving it above the line merely makes it more likely that the problem will show up. Bill Fairchild Rocket Software -----Original Message----- From: IBM Mainframe Assembler List [mailto:[email protected]] On Behalf Of Binyamin Dissen Sent: Thursday, March 10, 2011 7:11 AM To: [email protected] Subject: Re: TIOT On Thu, 10 Mar 2011 12:38:13 GMT "[email protected]" <[email protected]> wrote: :>The reason why I ask this question - I was informed that increasing the TIOT parmlib parameter from 32 to 64 created performance problems. :>What ? The change was not made by a CICS nor MVS Sys Prog, but from a DB2/DBA. Know one can tell me what exactly the performance issue was exactly. Not obvious to me why this would cause performance problems. Binyamin Dissen <[email protected]> http://www.dissensoftware.com
