About ACH (Additional Cache Hits) and ACM (Additional Cache Misses) .

THIS IS MY GESS ONLY!!!

When Oracle changed structure and ALGORITHMS of manage db buffer pool this
X$ tables(X$KCBCBH and X$KCBRBH), ACH and ACM has no sense.
When its parameters worked, DB cache had homogeneous structure.
Now (in Oracle 8i, 9i) it has heterogeneous structure with default, keep and recycle areas.
In addition, db buffer has two internal areas "hot" and "cold" blocks and
another algorithm(i named it "middle point", "official" name is Touch-Count).
These are main reasonces, why Oracle excluded X$KCBCBH and X$KCBRBH from dictionary
and why ACH/ACM doesn't work.