You are using Hybrid Columnar Compression for a table stored in a tablespace that is contained in
an Exadata-based ASM diskgroup. Identify three statements that correctly explain where the
compression and decompression can be done.
A.
Decompression can be done on the database servers.
B.
Compression can be done on the Exadata storage servers.
C.
Compression can be done on the database servers.
D.
Decompression can be done on the Exadata storage servers.
Explanation:
B:
*Exadata storage provides an advanced compression technology, Hybrid Columnar Compression,
that typically provides 10x, and higher, levels of data compression.
*The Exadata Storage Server (Exadata storage or Exadata cells) is used as
the storage for the Oracle Database in the Database Machine. It runs the Exadata Storage Server
Software that provides the unique and powerful Exadata technology including Smart Scan, Smart
Flash Cache, Smart Flash Logging, IO Resource Manager, Storage Indexes and Hybrid Columnar
Compression.
A, D:
*decompression/Queries run directly on Hybrid Columnar Compressed data does
not require the data to be decompressed
/Data that is required to satisfy a query predicate does not need
to be decompressed; only the columns and rows being returned
to the client are decompressed in memory
/The decompression process typically takes place on the Oracle
Exadata Storage Server in order to maximize performance and
offload processing from the database server.
Correct answer: A, C, D
With HCC, compression operations always occur on the compute nodes as data is inserted via direct path load/insert.
Decompression can take place on either the storage cells or the compute servers, depending on the access method,
volume of data being returned, rows and columns being retrieved, and so forth. In general, the following statements
are true:
When smart scans are used t • o access HCC segments, decompression occurs for the selected
rows and columns on the storage cells.
• When smart scans are not used, decompression takes place on the compute nodes; entire
compression units (think in terms of multiple blocks and many rows-per-block) are sent over
the storage interconnect, loaded into the database buffer cache, and uncompressed.
Oracle Database performs compression and decompression
Decompression is performed by Exadata Storage Server
Correct answer: A,C,D
a b d
A,C,D
Compression for HCC is always done on the compute node. Option C
Decompression is done on the Exadata Storage Server if Smart scan is used. Option D
Decompression is done on the compute node if Smart Scan is disabled, Option A
HCC occurs only when it is a direct path load, in which DML operation is bring directly written to storage layer rather than cache.
So, it make sence that compression is being taken place at storage layer only. Also HCC is a feature of Exadata storage server.
To correct correct answers are A, C , D
1. At database level compression is being performed using package DBMS_COMPRESSION
2. Compression information is being stored as part of metadata of tables in dba_tables
3. All 11.2.X.X and 12c RDBMS version supports EHCC, so this features is supported by RDBMS in conjuction with Exadata
A is right. decompression at compute node for HCC if not using smart scan
B is wrong. compression always at compute node
C is right. compression always at compute node
D is right. decompression can be done at cell node if HCC via smart scan,
so A.C.D. are correct
ACD