Which two symptoms related to the database buffer cache together indicate that there are many
full table scans happening? (Choose two.)
A.
too many buffer busy waits
B.
very low buffer cache-hit ratio
C.
very high buffer cache-hit ratio
D.
many waits on the db file scattered read event
A is wrong. buffer busy waits indicates too small buffer or less DB writer
B is right. hit ratio is low, full scan makes it aged out
C is wrong.
D is right. full scan cause db file scattered read
Consider poor hit ratios when large full table scans are occurring.
Database blocks accessed during a long full table scan are placed on the tail end of the Least Recently Used (LRU) list and not on the head of the list. Therefore, the blocks age out faster than blocks read when performing indexed lookups or small table scans.