Hi, This is the place to mention VSAM System Managed Buffering that could, possibly, auto-tune the access to BLSR if the open intention was set correctly by the programmer and enough region was available.
Best Regards, Yifat -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Joel C. Ewing Sent: Wednesday, April 04, 2012 9:13 PM To: [email protected] Subject: Re: VSAM help wanted for random reads On 04/04/2012 10:37 AM, Chip Grantham wrote: > We have an application like this, that is multiple record types in the > same KSDS. We found that if we had a FD for the type '4' records and > a FD for the type '5' records (that is two DDs pointing to the same > file), that each kept a separate sequence set in storage and it ran > faster. You might try it. > > Chip Grantham | Ameritas | Sr. IT Consultant | > [email protected] 5900 O Street, Lincoln NE 68510 | p: 402-467-7382 | c: 402-429-3579 | f: > 402-325-4030 > ... Unless you have something at your installation that automatically tunes VSAM buffer allocation, some kind of manual tuning in the JCL is almost always recommended, as the default VSAM buffer allocations tend to be terrible for performance. Just specifying an BUFFNI INDEX buffer count large enough to accommodate all index levels, plus additional buffers if the access pattern has multiple localities of reference, can do wonders for random access performance, even without going to BLSR. The default used to "guarantee" that random access to any VSAM file with data in more than one CA (and hence at least two levels of index) would require re-reading CI's for all the various index levels for each data record access. Just providing a few additional index buffers in such cases might be enough to cut the physical I/O's by a significant factor. -- Joel C. Ewing, Bentonville, AR [email protected] ---------------------------------------------------------------------- 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
