Bug 12633340 - RISK SESSION SPIKE - LIBRARY CACHE LOCK AND LIBRARY CACHE: MUTEX X ==> @ Readme Instructions: @ The patch must be enabled by setting event 12633340 to level 1. It can @ be set in the init.ora or via alter system. If set in the init.ora, @ please note that all events must be specified on consecutive lines. If @ set via alter system, it will take effect only for new sessions @ that connect after that point in time. @ . @ event="12633340 trace name context forever, level 1" @ . @ This patch amends an earlier fix that was made in bug 6769075. Due to @ that fix, cursor reloads may take longer in a highly concurrent environment @ if that cursor was invalidated due to a DDL operation. With this patch, @ the reload issue should be fixed and it should resolve the related mutex @ contention. Note that this patch is not meant to eliminate all mutex @ contention in general. It should however eliminate or minimize mutex @ and library cache lock waits associated with the "build lock" for @ the cursor after DDL has occurred. Bug 16870682 - ESSC: LIBRARY CACHE LOCK 60%, MUTEX X 20%, CONCURRENT DDL, DML, Q ON PT ==> @ I would say all three changes helped but is mostly the event 12633340, level @ 4 which seems to have the greatest share