Oracle OCP 1Z0 053 Q105(Table Compression)
105.Which statements are true regarding table compression? (Choose all that apply.)
A. It saves disk space and reduces memory usage.
B. It saves disk space but has no effect on memory usage.
C. It incurs extra CPU overhead during DML as well as direct loading operations.
D. It incurs extra CPU overhead during DML but not direct loading operations.
E. It requires uncompress operation during I/O.
Answer: AC
E：I/O时，不需要额外的解压操作。因为在cache里就是压缩的。
Please note that there is common misconception that 11g table compression decompresses data while reading and holds it in the uncompressed form in the cache. That is not quite correct since one of the salient features of the database compression is that we do not have to uncompress the data before reading it and the data stays in the compressed form even in the cache.
参考：http://www.dba-oracle.com/oracle11g/sf_Oracle_11g_Data_Compression_Tips_for_the_DBA.html
A. It saves disk space and reduces memory usage.
B. It saves disk space but has no effect on memory usage.
C. It incurs extra CPU overhead during DML as well as direct loading operations.
D. It incurs extra CPU overhead during DML but not direct loading operations.
E. It requires uncompress operation during I/O.
Answer: AC
E：I/O时，不需要额外的解压操作。因为在cache里就是压缩的。
Please note that there is common misconception that 11g table compression decompresses data while reading and holds it in the uncompressed form in the cache. That is not quite correct since one of the salient features of the database compression is that we do not have to uncompress the data before reading it and the data stays in the compressed form even in the cache.
参考：http://www.dba-oracle.com/oracle11g/sf_Oracle_11g_Data_Compression_Tips_for_the_DBA.html
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