What this 256-byte ""warning"" is telling you is that you are susceptible to a
S0C4 abend if you use a sort-key variable that is less than 256 bytes long
and is allocated less than 256 bytes from the end of a physical 4K page
boundary.
The reason for this potential S0C4 is that if your program does not ""own""
the next physical 4K page, when 256 bytes are moved the move would start on
a page that you own, but the end of the move would be on a page that you do
not own. Somewhere during the execution of the move you will cross the
physical 4K page boundary of storage to a page you don't own and will get
the S0C4 abend when this occurs.
When coding an OBTAIN USING SORT-KEY, remember that you can only have a
single variable in the SORT-KEY clause. If your INDEX or SORTED set has a
key built of multiple values, you must supply a GROUP level SORT-KEY
variable and each element within the group must match the picture and order
of the individual sort keys. This is noted in the second NOTE following the
NOTE already cited by Chris.
Chuck