Oracle 11g Database New Features: Data Guard Enhancements

Oracle 11g Database New Features: Data Guard Enhancements
Virag Sharma virag123@gmail.com

Why We need Data Guard ?? for

• Data protection
• Data Availability

11g Increase ROI from standby systems and enhance manageability, New feature like Active Data Guard , Snapshot standby make better ROI.

Here is some data guard category and there enhancement

1) Data Protection

• Advanced Compression
• Lost-write protection
• Fast-Start Failover

2) Increase ROI

• Active Data Guard
• Snapshot Standby

3) High Availability

• Faster Redo Apply
• Faster failover & switchover
• Automatic Failover using ASYNC

4) Manageability

• Mixed Windows/Linux

Active Data Guard

Oracle Active Data Guard 11g – a new Database Option
Enables read-only access to a physical standby database while Redo Apply is active
It is now possible to query a physical standby database while Redo Apply is active.This new capability increases your return on investment in Data Guard technology because a physical standby database can now be used to offload queries from the primary database in addition to providing data protection.
( We can do same with logical standby , what is diffrent here , well redo apply method is faster in physical stand by ie redo apply methode is diffrent in physical standby)

• Stop log apply

Alter database recover managed standby database cancel;

• Open database for read-only access

alter database open

• Once database open start redo apply

alter database recover managed standby database
using current logfile disconnect from session;


Snapshot Standby

This enhancement is good example of ROI. This feature allow us to better utilization of standby. This feature Truly leverages DR hardware for multiple purposes.For example convert physical database to snapshot standby database do testing/ application patching etc. After testing convert back snapshot database back to physical standby.

• -- Convert physical database to snapshot

ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;

• --
• -- Do testing on database
• --

• -- Convert snapshot Database to physical database

ALTER DATABASE CONVERT TO PHYSICAL STANDBY;

This Similar to storage snapshot , but it useage same space , not additional space is needed ( I know this possibly can achieve in 10g R2 too , using flashback feature , But for sure it is not easy as it is in 11g )


Redo compression

To transport redo data in compressed form to destination use COMPRESSION attribute.
By default compression is disabled.

• Alter system set log_archive_dest_1 = 'SERVICE=standby1 compression=ENABLE';
  
  
• select dest_name , compression from v$archive_dest;
  
  SQL>
  DEST_NAME COMPRES
  --------------------------------- -------
  LOG_ARCHIVE_DEST_1 DISABLE
  LOG_ARCHIVE_DEST_2 ENABLE
  LOG_ARCHIVE_DEST_3 DISABLE
  LOG_ARCHIVE_DEST_4 DISABLE
  LOG_ARCHIVE_DEST_5 DISABLE
  LOG_ARCHIVE_DEST_6 DISABLE
  LOG_ARCHIVE_DEST_7 DISABLE
  LOG_ARCHIVE_DEST_8 DISABLE
  LOG_ARCHIVE_DEST_9 DISABLE
  LOG_ARCHIVE_DEST_10 DISABLE
  
  10 rows selected.
  

Data Protection

New Initialization parameter db_lost_write_protect Introduced. This parameter Compare versions of blocks on the standby with that in the incoming redo stream
Version discrepancy implies lost write on either primary or standby database

db_lost_write_protect

Managibilty Enhancement

SYS user and password files no longer required for redo transmission authentication. Non-SYS user can be specified through the parameter, This user must have the SYSOPER privileges, Requires password for this user to be the same at primary and all standbys
Upon SYSDBA / SYSOPER changes, password file must be copied from the primary to all physical standby databases

redo_transport_user

Data Guard Support for Heterogeneous Primary and Standby Systems in Same Data Guard Configuration (- Since 11g Linux installer only available, so not able to test this feature)

Fast-Start Failover

Immediate automatic failover for user-configurable health conditions



DGMGRL> show FAST_START FAILOVER
DGMGRL> ENABLE FAST_START FAILOVER [CONDITION ];

Condition examples:

• Datafile Offline
• Corrupted Controlfile
• Corrupted Dictionary
• Inaccessible Logfile
• Stuck Archiver
• Any explicit ORA-xyz error

Application can also request for failover using package DBMS_DG

DBMS_DG.INITIATE_FS_FAILOVER