When creating keyed files or indexes using the Create Physical File (CRTPF) or Create Logical File (CRTLF) commands, or the SQL CREATE INDEX statement, you can use the PAGESIZE parameter to specify the access path logical page size that is used by the system when the access path is created.
This logical page size is the amount of bytes of the access path that can be moved into the job's storage pool from the auxiliary storage for a page fault.
You should consider using the default of *KEYLEN for this parameter except in rare circumstances so that the page size can be determined by the system based on the total length of the key, or keys. When the access path is used by very selective queries (for example, individual key look up), a smaller page size is typically more efficient. Also, when the keys being selected by queries are grouped together in the access path and many records are being selected, or the access path is being scanned, a larger page size is typically more efficient.