Exadata : Hybrid
Columnar Compression
Introduction
Hybrid
Columnar Compression (HCC) is a storage-related Oracle Database feature that
causes the database to store the same column for a group of rows together.
Its storing column data together in this way can dramatically
increase the storage savings achieved from compression. Because database
operations work transparently against compressed objects, no application
changes are required.
The HCC feature is available on database deployments created on Oracle Database Cloud Service using
the Enterprise Edition - High Performance or Enterprise Edition - Extreme
Performance software edition
Purpose
·
Hybrid Columnar Compression on Exadata enables
the highest levels of data compression and provides enterprises with tremendous
cost-savings and performance improvements due to reduced I/O.
·
HCC is optimized to use both database and
storage capabilities on Exadata to deliver tremendous space savings AND
revolutionary performance.
·
Average storage savings can range from 10x to
15x depending on which Hybrid Columnar Compression level is implemented
Best usage in data
warehouse bulk loading techniques.
To maximize storage savings with Hybrid Columnar
Compression, data must be loaded using data warehouse bulk loading techniques.
Examples of bulk load operations commonly used in data warehouse environments
are:
- Insert statements with the APPEND hint
- Parallel DML
- . Direct Path SQL*LDR
- . Create Table as Select (CTAS)
Queries on hybrid columnar compressed data often run in the
Exadata storage cells with Smart Scans, using a high performance query engine that
utilizes special columnar processing techniques.
Note
Data remains
compressed not only on disk, but also remains compressed in the Exadata Smart
Flash Cache, on Infiniband, in the database server buffer cache, as well as
when doing back-ups or log shipping to Data Guard.
The best part of this feature is data process without
sacrificing the robust feature set of the Oracle Database.
Note that while data in Hybrid Columnar compressed tables
can be modified using conventional DML operations - INSERT, UPDATE, DELETE
Migration
and Best Practices
Building
type of compression in tables as per business requirement
·
COMPRESS FOR QUERY HIGH
·
COMPRESS FOR QUERY LOW
·
COMPRESS FOR ARCHIVE LOW
·
COMPRESS FOR ARCHIVE HIGH
For new tables and partitions, enabling Hybrid Columnar
Compression is as easy as simply Creating the table or partition and specifying
a compression level, such as “COMPRESS FOR QUERY HIGH”.
Example:
CREATE TABLE dbaocm (sno NUMBER, ename VARCHAR2(128), dept
VARCHAR2(128)) COMPRESS
FOR QUERY HIGH;
CREATE TABLE dbaocm (sno NUMBER, ename VARCHAR2(128), dept
VARCHAR2(128)) COMPRESS
FOR QUERY LOW;
CREATE TABLE dbaocm (sno NUMBER, ename VARCHAR2(128), dept VARCHAR2(128))
COMPRESS FOR ARCHIVE LOW;
CREATE TABLE dbaocm (sno NUMBER, ename VARCHAR2(128), dept
VARCHAR2(128)) COMPRESS
FOR ARCHIVE HIGH;
Practice
1.
Establish
a terminal connection to 192.168.1.140 (rac140.ora.com) exadata compute node as
the oracle user.
2.
Connect
to your database with SQL*Plus. Login as the sh user.
[oracle@192.168.1.140
~]$ sqlplus sh/sh
3.
Determine
the size of the uncompressed INVENTORY table in sh schema
SQL> SET LIN200 PAGES
200
COL SEGMENT_NAME FORMAT
A40
SELECT SEGMENT_NAME,
SUM(BYTES)/1024/1024 SIZE_MB
FROM USER_SEGMENTS
WHERE SEGMENT_NAME LIKE
'INVENT%'
GROUP BY SEGMENT_NAME;
SEGMENT_NAME SIZE_MB
----------------------------------------
----------
INVENTORY 366
4.
Verify
that the INVENTORY table is uncompressed
SQL> select table_name,
compression, compress_for
from user_tables
where table_name like
'INVENT%';
TABLE_NAME COMPRESS COMPRESS_FOR
------------------------------
-------- ------------
INVENTORY DISABLED
5.
Exadata
Hybrid Columnar Compression achieves its highest levels of compression with
data that is direct-path inserted.
alter session force
parallel query;
alter session force
parallel ddl;
alter session force
parallel dml;
6.
Create
a compressed copy of the INVENTORY table using the QUERY HIGH warehouse compression
mode.
SQL> CREATE TABLE
INVENT_QUERY
COMPRESS FOR QUERY HIGH
PARALLEL 4 NOLOGGING
AS SELECT * FROM
INVENTORY;
Table created.
7.
Create
a compressed copy of the INVENTORY table using the ARCHIVE HIGH archive
compression mode.
SQL> SQL> CREATE
TABLE INVENT_ARCHIVE
COMPRESS FOR ARCHIVE HIGH
PARALLEL 4 NOLOGGING
AS SELECT * FROM
INVENTORY;
Table created.
8.
Verify
the compression mode settings for the tables just created
SQL> SELECT TABLE_NAME,
COMPRESSION, COMPRESS_FOR
FROM USER_TABLES
WHERE TABLE_NAME LIKE
'INVENT%';
TABLE_NAME COMPRESS COMPRESS_FOR
------------------------------
-------- ------------
INVENT_QUERY ENABLED QUERY HIGH
INVENT_ARCHIVE ENABLED ARCHIVE HIGH
INVENTORY DISABLED
Compare the size of the original uncompressed table with the
two compressed copies you created. Calculate the compression ratios achieved
using the formula:
SQL> SELECT SEGMENT_NAME,SUM(BYTES)/1024/1024 MB
SQL> SELECT SEGMENT_NAME,SUM(BYTES)/1024/1024 MB
FROM USER_SEGMENTS
WHERE SEGMENT_NAME LIKE
'INVENT%'
GROUP BY SEGMENT_NAME;
SEGMENT_NAME MB
----------------------------------------
----------
INVENTORY 366
INVENT_ARCHIVE 34.1875
INVENT_QUERY 55
So here we can easily see the size
of tables using HCC which is having same number of rows in different size ,
which gives 10X storage saving using HCC
storage feature.
CONSLUSION
The massive growth in data volume, experienced by
enterprises, introduces significant challenges. Industries must quickly adapt to the changing business
landscape without influencing the bottom line. Its responsibility of IT
managers need to efficiently manage their existing infrastructure to control
costs and deliver extraordinary application performance. Advanced Compression provide a robust set of compression,
performance and data storage optimization capabilities that succeed in this
complex environment.
