Hi all, Can anyone let me know w

[kurup]

Hi all,

Can anyone let me know what is the exact advantage in using VSAM...? Some questions are

1)Why and how was VSAM developed by IBM?
2)In case of IMS, DLI is used to opearate between OS and application program. The DLI transfers info about the DB func to be performed from program to OS and then OS internally uses VSAM to perform DB operation. In normal file handling the OS directly receives messages from the pgm. Then y are we using DLI in IMS...?

Thanks,
Kurup

 

[gongura]

Hi Kurup,

As far as I know,
1) file i-o operations are very fast in case of VSAM
2) Space organizations are being done effectively.

Rgds,
Koppala

 

[3gm]

Well, I can't answer all your questions, but . . . VSAM replaced ISAM (Indexed Sequential Method) back in the late 70s. VSAM had many more features, and was more robust than ISAM. It took advantage of Virtual Storage for example.

All data base managers use some form of keyed-file storage to enable random access to their underlying data. As IBM has wont to do, they leveraged their existing access method for keyed files when developing DL1 rather than design a new access method.

Glenn

 

[kurup]

Thanks for your reply kopala and glenn. Any site u know which gives more details on VSAM??

Thanks
Kurup

 

[slade]

Hi Kurup,

As Tom stated, VSAM was developed by IBM as a replacement for ISAM which was reputed to be slow.

As a matter of fact, just the other day I saw ISAM defined as the Incredibly Slow Access Method and VSAM as the Very Slow Access Method .

Where VSAM/ISAM/QSAM/BSAM/etc. are access methods, IMS/DB2/IDMS/SYBASE/etc. are considered database mgmt systems. Where one leaves off and the other begins, I'm not sure.

Regards, Jack.

P.S. VSAM is used in the DB2 process.

 

[3gm]

The OS/390 documentation library has lots of stuff on VSAM. You can read it at:

http://www-1.ibm.com/servers/s390/os390/bkserv/