Oracle Advanced Compression

Oracle Advanced Compression and Oracle Database 11g Release 2 helps manage more data in a cost-effective manner. With data volumes, on average, tripling every two years, Oracle Advanced Compression delivers compression rates of 2-4x across all types of data and applications.storage savings from compression will cascade throughout the data center, reducing network traffic and data backups as well. And by reading fewer blocks off disk, Oracle Advanced Compression also improves query performance.

Oracle Advanced Compression is an option of the Oracle 11g database (separately licensed) that allows data in the database to be compressed. Oracle Advanced Compression offers the following advantages:

1.) OLTP Compression  : It allows structured and unstructured data to be compressed on insert,update and delete  operations.The following are features : 

• New compression algorithm uses deferred or batched approach
• Data is inserted as is without compression until  PCTFREE  value is reached.
• Compression of data starts once PCTFREE threshold is reached
• Can be enabled at  table, partition or tablespace level
• No need of decompressing the data during reads
• Recommended for low update activity tables

2.) Data Pump Compression   : In Data Pump, the compression of metadata was introduced in 10g and compression of "data" was introduced in 11g.This covers the following features : 

• Both are Inline operation
• Save on storage allocation
• No need to uncompress before Import
• Implemented with COMPRESSION attribute, Values supported are ALL, DATA_ONLY, METADATA_ONLY . 

3.) Data guard Compression : It includes the following features : 

• Redo is compressed as it is transmitted over a network .
• Helps efficiently utilize network bandwidth when data guard  is across data centers
• Faster re-synchronization of Data guard  during gap resolution.
• Recommended for low network bandwidth .
• Implemented with attribute “COMPRESSION”  of initialization parameter log_archive_dest_n

.4.) RMAN Backup Compression  : It compresses the RMAN backups.The followinf features are

• Supports compression of backups using "ZLIB"  algorithm .
• Faster compression and low CPU utilization compared to default BZIP2 (10g) .
• Low compression ratio  compared to BZIP2 .
• Implement  with  CONFIGURE COMPRESSION ALGORITHM  ‘value’ command where value can be High , Medium(ZLIB) and Low(LZO) .

The Oracle Database 11g Advanced Compression option introduces a comprehensive set of compression capabilities to help customers maximize resource utilization and reduce costs. It allows IT administrators to significantly reduce their overall database storage footprint by enabling compression for all types of data – be it relational (table), unstructured (file), or backup data . Although storage cost savings are often seen as the most tangible benefit of compression, innovative technologies included in the Advanced Compression Option are designed to reduce resource requirements and technology costs for all components of our IT infrastructure, including memory and network bandwidth .

The benefits of compression are manyfold
1.) Reduction of disk space used for storage .
2.) Reduction in I/O bandwidth requirements .
3.) Faster full table scans .
4.) Lower server memory usage.


Enjoy    J J J

Change Database Character Set using CSSCAN

CSSCAN (Database Character Set Scanner) is a SCAN tool that allows us to see the impact of a database character set change or assist us to correct an incorrect database nls_characterset setup. Data scanning identifies the amount of effort required to migrate data into the new character encoding scheme before changing the database character set. This information helps to determine the best approach for converting the database character set.

Before altering the character set of a database, check the convertibility of the data before converting. Character set conversions can cause data loss or data corruption. The Character Set Scanner utility provides the below two  features: 

1.) Convertibility check of existing data and potential issues. The Scanner checks all character data in the database including the data dictionary and tests for the effects and problems of changing the character set encoding (characterset). At the end of the scan, it generates a summary and exception report of the database scan.

2.) Csscan allows  also us to do a check if there is no data in the database that is  incorrectly stored.

The CSALTER script is part of the Database Character Set Scanner utility. The CSALTER script is the most straightforward way to migrate a character set, but it can be used only if all of the schema data is a strict subset of the new character set. Each and every character in the current character set is available in the new character set and has the same code point value in the new character set.

With the strict superset criteria in mind, only the metadata is converted to the new character set by the CSALTER script, with the following exception: the CSALTER script performs data conversion only on CLOB columns in the data dictionary and sample schemas that have been created by Oracle. CLOB columns that users have created may need to be handled separately

Note :  it's possible to run Csscan from a client, but this client needs to be the same base version as the database home.(i.e, oracle 11g server need oracle 11g client) .

To change the database character set, perform the following steps :


STEP 1 : Remove the invalid objects and purge the recyclebin , then take a  full backup of the database.

STEP 2 : Install the CSS utility if not install . We will get error css-00107 if css utility is not install .Install the CSS utility by running the csminst.sql script which is found in $ORACLE_HOME\rdbms\admin .

STEP 3 : Run the Database Character Set Scanner utility as
set the oracle_sid and run as
CCSSCAN  /AS SYSDBA  FULL=Y


STEP 4 : Run the CSALTER script.This script is in $ORACLE_HOME\rdbms\admin  folder .
i.>   shut down 
ii.>  startup restrict 
iii.> @csalter.plb
iv.> shut immediate
v.>  startup  

Note :  

i.> The CSALTER script does not perform any user data conversion. It only changes the character set metadata in the data dictionary.Thus, after the CSALTER operation, Oracle will behave as if the database was created using the new character set.

ii.> Changing the database characterset is not an easy task . It is quite tricky tasks and may face errors which need the oracle support . So,it's better to raise as SR for this task and involve the  oracle support .  

There  are no of links on meta-link .Check the below meta-links .

Note: 555823.1 – Changing US7ASCII or WE8ISO8859P1 to WE8MSWIN1252
Note: 444701.1 – Csscan output explained
Note: 745809.1 – Installing and configuring Csscan in 10g and 11g (Database Character Set Scanner)
Note: 225912.1 – Changing the Database Character Set ( NLS_CHARACTERSET ) [ID 225912.1]




Enjoy   J J J

Append Date & time to File name in Window Batch file

Sometimes it may be required to schedule the same task twice a days . In such cases, we have to create two batch file and scheduling them separately because the generated name may overwrites or throws errors . To overcome from this issue , we can schedule the same task with single batch file. Suppose we have to take the logical backup of a schema(say scott) twice a days . We can do this by simply appending the date and time to the dump file name .

As in case of Linux /Unix systems, shell scripting is very liberal with variables and we can define according to ourself . e.g;
expdate=`date ‘+%d%m%Y’`
dat=`date ‘+%m%d%y %H:%M:%S’`

And then go onto define in our script as

./expdp system/xxxx  dumpfile=scott_$expdate.dmp logfile=scott_log_$expdate.log schemas=scott

But on windows machine ,we use the Date and Time function. The Date and Time function are as below  :

Date:  %date:~4,2%-%date:~7,2%-%date:~12,2%
Time:  %time:~0,2%-%time:~3,2%-%time:~6,2%  

This above function can be use to generate the unique dumpfile name. Below is the Demo of this function .

c:\> exp system/ramtech@noida  owner=scott  file=c:\scott_%date:~4,2%-%date:~7,2%-%date:~12,2%-%time:~0,2%-%time:~3,2%-%time:~6,2%.dmp log=c:\scottlog_%date:~4,2%-%date:~7,2%-%date:~12,2%-%time:~3,2%-%time:~6,2%.log    

The file name generated  i.e, dump file name is 'scott_12-22-11-12-04-31.dmp'  and log file name is 'scottlog_12-22-11-04-31.log'    where date is 12-22-11(12th-dec-2011) and time is 12-04-31(12hr:4min:31sec) .

Enjoy    J J J