IBM Mainframe Forum

I would like to intercept VSAM reads that occur in batch COBOL programs and direct them to an alternate data access method. So far, I'm not having any success. VSAM exits are driven after data is accessed, as far as I can tell. I need to get the commands BEFORE they are executed. Any ideas?

The question is: Why would you want to do that??

It's part of proof of concept for a performance enhancement product.

It most certainly is possible. The IAM product does it every day.

Even if I knew how they do it, I certainly would not disclose it here!

Hello,

Quite a few products do this.

VSAM commands are intercepted before vsam data is addressed. The intercept looks at some control table (in some load module or stored data) and determines whether to re-route the vsam command elsewhere or continue to the normal vsam processing.

Some of the products that do this call it "VSAM Transparency". For example, cobol code that "works with vsam" will run unchanged against a database if that database supports vsam transparency.

IAM and other VSAM transparency products simply front-end the VSAM executable. I'd like to be able to do that, but that's not what this proof of concept is attempting to prove.

how can you do/code performance enhancement if you do not have the knowledge to even front end VSAM?

Surely you need to implement the product and test it agaianst the current methodology in place and compare the results.

littlechicken wrote:how can you do/code performance enhancement if you do not have the knowledge to even front end VSAM?

Front-ending VSAM is easy; just module substitution of the main VSAM executables. Doing it without swapping modules is a lot more involved.

expat wrote:Surely you need to implement the product and test it agaianst the current methodology in place and compare the results.

Huh??? There is no current methodology for intercepting VSAM without module substitution and if I could implement this product I wouldn't be here asking.