1Z0-060 Latest Exam Braindumps
Question 18: You notice a high number of waits for the db file scattered read and db file sequential readevents in the recent Automatic Database Diagnostic Monitor (ADDM) report. After further
investigation, you find that queries are performing too many full table scans and indexes are not
being used even though the filter columns are indexed.
Identify three possible reasons for this. (Choose three.)
A. Undersized shared pool
B. Missing or stale histogram statistics
C. High value for the DB_FILE_MULTIBLOCK_READ_COUNT parameter
D. High clustering factor for the indexes
E. Oversized buffer cache
Correct Answer: B,C,D
Explanation
D: DB_FILE_MULTIBLOCK_READ_COUNT is one of the parameters you can use to minimize I/O during
table scans. It specifies the maximum number of blocks read in one I/O operation during a sequential
scan.
The total number of I/Os needed to perform a full table scan depends on such factors as the size of
the table, the multiblock read count, and whether parallel execution is being utilized for the
operation.
