VSAM Media Manager
On Mon, Apr 21, 2014 at 4:49 PM, Bernd Oppolzer <[email protected]>wrote: > I know that DB2 does not use VSAM KSDS - only for very limited purposes, > IIRC - some logfile directories or boot strap data sets, don't recall the > details. > > The tablespace data sets are VSAM LDS - linear data sets. > > Anyway: there are some improvements done to VSAM for DB2, AFAIK ... > I believe some improvements to enable list prefetch or other things I don't > recall at the moment ... and I recall only vaguely a paper from ORACLE > where > they tell that they benefit from these VSAM improvements, too. > > Kind regards > > Bernd > > > > Am 21.04.2014 16:59, schrieb Joel C. Ewing: > >> I'm pretty sure the original motivation behind VSAM was to provide a >> more efficient keyed-access alternative to an earlier ISAM (Indexed >> Sequential Access Method) keyed-access method --ISAM had abysmal >> performance when the number of inserts became large. But, just as a >> clarification, while it is true that VSAM under IBM Operating systems >> includes support for keyed-access data sets in the forms of KSDS (Keyed >> Sequential) and RRDS (Relative Record), VSAM also includes support for >> non-keyed-access data set types: ESDS (Entry-Sequenced) and LDS >> (Linear). >> >> The LDS data sets on z/OS do not have any organizational structure >> imposed upon them by VSAM other than being a stream of consecutive bytes >> physically organized in 4KiB, pageable chunks; and DB2 uses these LDS >> data sets for its table spaces. So, it is incorrect to think of DB2 as >> somehow using or building upon VSAM keyed-access techniques to locate >> table rows. DB2 has it own table structures, indexing organization, and >> key search techniques built on top of the very rudimentary Linear Data >> Set structure. >> >> DB2 required greater flexibility and control to achieve its performance >> and data consistency goals than was possible with VSAM keyed-access >> support. A very cursory look at "Experiences Installing Oracle >> Database 10g on z/OS" would suggest Oracle on z/OS makes use of VSAM LDS >> for table storage as well. >> Joel C Ewing >> > > ---------------------------------------------------------------------- > 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
