Which types of data are most likely to be cached In the Exadata Smart Flash Cache?
A.
Results of random reads.
B.
Results of table scans.
C.
Write to a mirror
D.
Redo data
E.
All data is cached In the Flash Cache
Explanation:
The Oracle Database and Exadata Storage Server Software work closely together
to cache frequently accessed data. When the database sends a read or write request to Sun
Oracle Exadata Storage Server, it includes additional information in the request about whether the
data is likely to be read again and therefore whether it should be cached. Based on the information
the database sends the Exadata Storage Server Software intelligently decides which data will be
re-read, and is worth caching, and those operations that would just waste cache. Random reads
Exadata Smart Flash Cache and the Sun Oracle Database Machine
against tables and indexes are likely to have subsequent reads and normally will be cached
and have their data delivered from the flash cache.Scans, or sequentially reading tables,generally would not be cached since sequentially accessed data is unlikely to be subsequently
followed by reads of the same data. Write operations are written through to the disk and staged
back to cache if the software determines they are likely to be subsequently re-read.
Knowing what not to cache is of great importance to realize the performance potential of the
cache. For example, when writing redo, backups or to a mirrored copy of a block, the
software avoids caching these blocks. Since these blocks will not be re-read in the near
term there is no reason to devote valuable cache space to these objects or blocks. Only the
Oracle Database and Exadata Storage Server software has this visibility and understands the
nature of all the I/O operations taking place on the system. Having the visibility through the
complete I/O stack allows optimized use of the Exadata Smart Flash Cache to store only the most
frequently accessed data.
All of this functionality occurs automatically without customer configuration or tuning and in most
cases is the best use of the Exadata Smart Flash Cache.
http://www.oracle.com/technetwork/middleware/bi-foundation/exadata-smart-flash-cache-twp-v5-1-128560.pdf