Performance Tuning - Question 095

Which three statements about improving the performance of the database buffer cache by creating multiple buffer pools are true? (Choose three)

A. One, two, or three pools may be defined.

B. There are at least 50 blocks per LRU latch for each pool.

C. Each buffer pool is assigned latches taken from DB_BLOCK_LRU_LATCHES.

D. The size if the DEFAULT pool is obtained by adding all the pools to the value of the DB_BLOCK_BUFFERS parameter.

Answer: A, B, C

Explanation:

Unless you specify otherwise in the init.ora, only the Default Pool is created at instance startup. But Oracle provides you also with the ability to divide the Database Buffer Cache into as many as three separate areas called Buffer Pools: Keep Pool (optional), Recycle Pool (optional) and Default Pool (mandatory). There are at least 50 blocks per LRU latch for each pool. Also each buffer pool is assigned latches taken from DB_BLOCK_LRU_LATCHES.

Incorrect Answers

D: Default Pool is used to cache segments that are not designated for either the Keep or Recycle pools. The size of this pool is designated in bytes, kilobytes, megabytes, or gigabytes, by the init.ora parameter DB_CACHE_SIZE. Unlike Oracle8i, where the memory for the Keep and Recycle pools was taken from the memory allocated to the Default Pool, Oracle9i independently assigns the memory to each of the three Buffer Pool types.

OCP: Oracle 9i Performance Tuning Study Guide, Joseph C. Johnson, p. 265-266, 468-476

Chapter 5: Tuning the Database Buffer Cache, Chapter 9: Tuning Contention