NCL VSAM Techniques › Concurrent Access to Multiple UDBs

Concurrent Access to Multiple UDBs

An NCL procedure can actively process several UDBs at a time. The mandatory ID= operand on the &FILE verbs, indicates which UDB the verb is to be actioned upon. Each file must be opened separately, using an &FILE OPEN statement before reads and writes can be performed on it. There is no overhead in processing several files simultaneously, because NCL merely swaps pointers between the work buffers and RPLs used for each file, according to the ID specified on the &FILE verb.

Current keys and data set positioning are remembered by NCL when processing swaps from one file to another, so it is not necessary for the NCL procedure to remember these.

The example in the next section, of copying one file to another, shows how processing can be alternated between two files.