High wait event ‘row cache mutex’ in 12cR2、19c

In Oracle 12.2.0.1.0 (12cR2), “row cache mutex” replaced 12.1.0.2.0 (12cR1) and 11g  “latch: row cache objects”, similar to “latch: library cache” substitution by “library cache: mutex X” in the previous release.

P1TEXT = cache id ，”cache id” can be used to directly pinpoint the exact contention row cache objects. v$rowcache.cache#(x$kqrst.kqrstcln)

SQL> select cache#,type,PARAMETER,gets,getmisses,flushes from V$ROWCACHE where cache#=10;

    CACHE# TYPE        PARAMETER                              GETS  GETMISSES    FLUSHES
---------- ----------- -------------------------------- ---------- ---------- ----------
        10 PARENT      dc_users                              38441        113          0

12cR2 v$rowcache contains 71 rows, 19c（19.3）contains 75 rows, 20c(20.2) contains 76 rows.

High waits on “row cache mutex” when looking up user or role information in user row cache (dc_users). hit Bug 30623138.

if row cache dc_props or dc_cdbprops and the sessions are using dblinks. may hit Bug 30712670.

More about latch: row cache objects Troubleshooting “latch: row cache objects” case and Event 10089 to do.