This document describes how to resolve an error message during a cache refresh.
What to do if I get this error msg during cache refresh?
"All buckets for <your cached resource> are in use! Cannot perform cache refresh"
Look at all the rows in the cache_status table, WHERE resourceid = <your cached resource>
If you see a row for every configured bucket with a status of C or A, then you may have an existing client session that is still connected to CIS and holding a read lock on that bucket with a status of C. Clear out the completed sessions and check if that releases any buckets.
If you are permitted, clear the cache and look for any rows in the cache status table where the status is still C.