In mysys/mf_keycache.c special debugging macros like KEYCACHE_DBUG_PRINT are defined and used. These should be replaced by DBUG macros. The DBUG macros in mf_keycache.c can use the label "key_cache". Keycache debugging can then be activated by --debug=i:d,key_cache:O,trace_file. The option 'i' enables the thread tracing which is part of the KEYCACHE_ macros, though with a different layout. This task was created on request from Monty during the review to BUG#10602 (LOAD INDEX INTO CACHE deadlocks) on 2005-06-01. It can also be done for 5.0 if it comes early enough.