Hello and welcome to the forum,
Could you please help me with the IDCAMS paramaters which will increase the Build performance of Alternate index.
Not from what you have posted. . . .
Posting "it doesn't work fast enough" will not get many/any usable replies.
How many records are there in the file? What do the define(s) for the file and the index entries look like (post them)? What is the difference in time required to load the file with and without this particular alternate index?
The better info you provide, the better suggestions we can make to help.