Arun, OK, looking at the full strobe report, if I read it correctly, converting to sequential processing may not be the most efficient way to process this. Both files have 32.4M records, but you only touch 4.9M records in each file when the program executes. You are touching around 15% of the total records in each file so a full sequential read of each may cost more CPU time., especially if you include the time to build redundant files.
The distribution of touched cylinders in both files is quite random, with IEHEYEBALL telling me that the distribution and clustering of touched cylinders are similar in both files. The clustered activity supports your finding that there is some efficiency from more data chaining for the skip sequential IO. I'm not sure what your objectives are for this. You have a program that processes 8 million records using 2 minutes of CPU time in a three minute period and doing 9.4K IO to each of the index and data components of both files. Strobe does not report the CPU model in your report, so I don't know if this is on z196-401, a z14-708, or something in between, but if you want an omelet, you have to crack a few eggs. The CPU time is not SRB time, which corresponds to the relatively low IO count. Strobe support can tell you why IGZEQBL mentions QSAM in the description, but it does not mean you are spending time in QSAM. My wife's laptop is an Apple, but I can't eat it - it's a label. I think that the time in IQZEQBL and IGZCPCO are simply the cost of reading 8 million records from the buffers and not related to the actual IO operations. You need to engage a Strobe expert or Compuware to dig deeper into this. Ron -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Chris Hoelscher Sent: Sunday, January 7, 2018 8:57 PM To: [email protected] Subject: Re: [IBM-MAIN] VSAM Performance - CPU reduction How 'bout ..... Flagging the matches that currently require the random read - and instead pass those records thru the 2nd file - both in this random key sequence - that would eliminate all random reads - yes another sort or 2 and another match pass - but in the past I have found the savings of replacing random reads with sequential access is substantial Chris Hoelscher Technology Architect, Database Infrastructure Services Technology Solution Services 123 East Main Street Louisville, KY 40202 Humana.com (502) 476-2538 or 407-7266 -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Wayne Bickerdike Sent: Sunday, January 7, 2018 4:18 PM To: [email protected] Subject: Re: [IBM-MAIN] VSAM Performance - CPU reduction Quote Apologies. I missed to mention that depending on a record that matches in the 2nd file, there are some random reads that refer back to a previous record as per the business logic. Hence, the second file has to be VSAM. We also see a similar behavior with few other programs that do skip sequential reads on other VSAM files. Unquote So do the two file match and utilise the VSAM (second file) for random read where it's required. You won't tune your way out of this. On Mon, Jan 8, 2018 at 6:03 AM, Gerhard Adam <[email protected]> wrote: > To me it still looks like you don't have enough index buffers. My > calculation suggests you need at least 137 buffers to keep the index > set in memory. > > > > Sent from my iPhone > > > On Jan 7, 2018, at 10:21 AM, Arun Venkatratnam < > [email protected]> wrote: > > > > Ron, > > > > About 80% of the records qualify from the second file. I tried > > running > the job with BUFND of 2 for the second file. It increased the EXCPs > significantly (from strobe report) on the data records for the 2nd > file and the CPU time went over the other runs and the elapsed time also > increased. > The job runs better with higher values of BUFND for the second file. > > > > You had mentioned that the job reads 30 CI for every skip-seq access. > Could you please tell how did you arrive at that number. LISTCAT shows > that for a CISZ of 26KB, there are 30 CI in 1 CA. > > > > > > Thanks > > Arun > > > > -------------------------------------------------------------------- > > -- For IBM-MAIN subscribe / signoff / archive access instructions, > > send email to [email protected] with the message: INFO > > IBM-MAIN > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, send > email to [email protected] with the message: INFO IBM-MAIN > -- Wayne V. 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