When a Joiner transformation occurs in a session, the Informatica Server reads all the records from the master source and builds index and data caches based on the master rows. After building the caches, the Joiner transformation reads records from the detail source and performs joins.
Joiner cache have 2 types of cache:
1.Index cache 2.Data cache.
Index cache stores all the port values which are participated in the join condition and Data cache have stored all ports which are not participated in the join condition.