> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:[email protected]] On Behalf Of Brown, Larry - > RD, St. Louis, MO > Sent: Thursday, July 19, 2012 7:22 AM > To: [email protected] > Subject: Problem Going to VSAM from IAM > > Hello, we have a job that was previously using Innovation's > IAM file access method. The file is over 6 million records. > The job runs twice yearly and usually takes an hour or less > to complete. The product was removed to save on SW costs, > and the file was converted to VSAM. The programmer did not > make any other changes, and the job now takes over 10 hours > to complete. I know the IAM product is supposed to improve > performance, but can't imagine it making the difference > between 1 and 14 hours run time. I'm suspecting there may > have been some JCL changes to blksize, buffers, and things > like that required, but the programmer is unaware of any of > those changes he should have made. The job is only reading > the file. Does anybody have any ideas on where to start > looking for other changes that should have been made after > converting from IAM to VSAM? The programmer is reviewing his > source code. Our performance support has not suggested > anything. Innovation claims %50-%80 reduction in processing > time, so maybe it is just a matter of IAM vs VSAM.(?) > > Here are the JCL and VSAM definitions: <snip> > Thanks, > > Larry Brown
Sequential reading or direct (keyed) reading or a combination of the two? I have had times, in a poorly designed program, where increasing the buffering resulted in __increased__ I/O and execution time. If the program is mainly doing direct (keyed) READs, then I'd suggest using the BLSR subsystem to use LSR buffering, or the AMP parameter of the DD statement to set the "access" correctly: http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/IEA2B6A0/12.4.1 //... AMP='AMORG,ACCBIAS=...' <quote> ACCBIAS=USER ACCBIAS=SYSTEM ACCBIAS=DO ACCBIAS=DW ACCBIAS=SO ACCBIAS=SW Specify one of these six values to override record access bias in the data class in order to use System-Managed Buffering (SMB) without changing the data class. See z/OS DFSMS Using Data Sets for details on System-Managed Buffering. USER Obtain buffers the same way the system would without SMB. This is the default if you code no specification for the ACCBIAS subparameter. SYSTEM Force SMB and let the system determine the buffering technique based on the ACB MACRF and storage class specification. Note: USER and SYSTEM are the only values you may use to specify record access bias in the data class. DO SMB with direct optimization. DW SMB weighted for direct processing. This option provides the capability to use hiperspace. SO SMB with sequential optimization. SW SMB weighted for sequential processing. SMBDFR=Y or SMBDFR=N With direct optimization, use this subparameter to instruct VSAM whether to defer writing of changed buffers to the medium until either the data set is closed or the buffers are required for some other request. See z/OS DFSMS Using Data Sets for further details on using SMBDFR. SMBHWT=nn Specify a requirement for hiperspace where nn is an integer from 0 to 99. Use this parameter with direct optimization. The default value is 0, which means that the system does not obtain any hiperspace. SMBVSP=nnK or SMBVSP=nnM Specify the amount of virtual buffer space to acquire for direct optimized processing when opening the data set, where nn is 1 to 2048000 kilobytes or 1 to 2048 megabytes. MSG=SMBBIAS When you specify MSG = SMBBIAS, the system issues message IEC161I to indicate which access bias SMB has chosen. The default is no message. </quote> -- John McKown Systems Engineer IV IT Administrative Services Group HealthMarkets(r) 9151 Boulevard 26 * N. Richland Hills * TX 76010 (817) 255-3225 phone * [email protected] * www.HealthMarkets.com Confidentiality Notice: This e-mail message may contain confidential or proprietary information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. HealthMarkets(r) is the brand name for products underwritten and issued by the insurance subsidiaries of HealthMarkets, Inc. -The Chesapeake Life Insurance Company(r), Mid-West National Life Insurance Company of TennesseeSM and The MEGA Life and Health Insurance Company.SM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
