Frank, Try using batch local shared resources (SUBSYS=BLSR) for the file, and specify at least twice as many index buffers for it as you have levels in the KSDS. For example:
//MYKSDS DD SUBSYS=(BLSR,'DDNAME=MYKSDS#','RMODE31=ALL', // 'MSG=I','BUFND=256','BUFNI=10') //MYKSDS# DD DSN=HLQ.MY.KSDS,DISP=SHR Where HLQ.MY.KSDS has 3 index levels. The BUFND counts data CI's that can be resident at the same time, adjust to suit your needs. The BUFNI is for index buffers (again CI's). Don't forget to increase REGION to account for the additional buffers in memory. Or you might try the new-fangled way, using SMB (system managed buffering). I haven't yet found that to be more helpful to performance than BLSR, but it might be worth your while to investigate it. See the JCL Reference manual for the parameters to use. HTH Peter -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Frank Swarbrick Sent: Tuesday, April 03, 2012 5:24 PM To: [email protected] Subject: VSAM help wanted for random reads Current program does the following (in COBOL!). - Opens KSDS for I-O - Sequentially processes another file (non-VSAM). - For each record in the non-VSAM file it attempts a random (keyed) read of a record on the KSDS file. The key is, essentially, a concatenation of a record type code ('4' or '5') and an account number. If no record of type '4' is found then it tries again for the same account, but with record type '5'. If either the '4' or '5' type is found it updates it and rewrites the record (assuming the data changed). This takes about 16 minutes to run. However if the 'type 5' logic is removed, so that it only ever looks for type '4' records, it takes only about one minute. Our resident VSAM expert says it has something to do with the VSAM "sequence set" and the fact that only one is kept in memory at a time. Since the same sequence set doesn't appear to be able to be used for both the 'type 4' records and the 'type 5' records it's constantly going back and forth, loading the "other" sequence set from disk. He says on VSE (which we were up until May 2010) more than one sequence set can be in memory, but with MVS this appears to not be the case. Hopefully that reason is accurate. Is there a solution? We thought about having two COBOL FDs pointing to two DDs, where both DDs pointed to the same KSDS. This would probably(?) work, except for the fact of the update. Thanks, Frank ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
