052-193(新增70题2018)

Users complain about the slow response time of queries. While investigating the cause you find that the Oracle Instance is not configured to cache all of the data blocks to satisfy the user's queries.
Which component of the Oracle Instance would you change to improve performance?
A. Java pool
B. Large pool
C. Shared pool
D. Streams pool
E. Library cache
F. Redo log buffer
G. Data dictionary cache
H. Database buffer cache
Answer: H

应该是database buffer cache不够导致缓存命中率低下要产生新的IO导致查询时间增长。

Database Buffer Cache

Oracle Database uses the buffer cache to achieve the following goals:

• Optimize physical I/O

  The database updates data blocks in the cache and stores metadata about the changes in the redo log buffer. After a COMMIT, the database writes the redo buffers to disk but does not immediately write data blocks to disk. Instead, database writer (DBW) performs lazy writes in the background.

• Keep frequently accessed blocks in the buffer cache and write infrequently accessed blocks to disk

  When Database Smart Flash Cache (flash cache) is enabled, part of the buffer cache can reside in the flash cache. This buffer cache extension is stored on a flash disk device, which is a solid state storage device that uses flash memory. The database can improve performance by caching buffers in flash memory instead of reading from magnetic disk.