1. Oracle DataGuard Concepts and Architecture
Brian Hitchcock OCP 10g DBA
Sun Microsystems
Brian Hitchcock October 23, 2007
Page 1

2. Oracle DataGuard Maintains a standby database Simple idea
Archived redo logs on primary
Sent to standby and applied
Simple idea
Many configuration options
No attempt to cover them all here
Discuss several specific sets of options
Can become very complicated

3. Oracle DataGuard Comes in Two Flavors Physical Standby Logical Standby
When I was young this was all we had…
Read-only when not applying redo logs
Logical Standby
Can be read-write while applying redo logs
Can add db objects to standby
Indexes for reporting
Many options

4. Themes What is a standby? When is a standby not a standby?
‘standby’ implies specific capabilities
Ready for failover
Complete copy of primary
No need to verify standby before failover
When is a standby not a standby?
When it doesn’t provide what name implies

5. What is a standby database?
Database that we can fail over to
Kept closely synchronized with primary db
Up to the minute
Once a day
Primarily dedicated to being ready for failover
May also be used for reporting
Guaranteed to be an exact copy
To the point of last synchronization
Can catch up as long as redo logs available

6. What is a standby database?
No question about standby
Is it a complete copy?
Is it ready for failover
Standby for reporting
Is standby providing accurate data for reports?
No one can change standby
No changes to data/objects in standby
If changes made to standby
Should be very obvious

7. Before DataGuard? Scripts, cron jobs
Copy archived redo logs from primary to standby
Apply redo logs on standby periodically
When script(s) executes
Standby db can’t be used for anything else
Constantly recovering
Failover
Open standby db with resetlogs
Can’t be standby again without rebuild
Can’t fail back to primary without rebuild

8. Standby Primary Database Standby Database Online Redo Logs Archived
Can’t change standby db objects
Primary
Database
Standby
Database
Standby mounted, recovering
Can only be opened resetlogs
Once opened, can’t switch back
Online Redo
Logs
Scripts, Cron Jobs
Archived
Redo Logs
Archived
Redo Logs

9. Why DataGuard? Part of Oracle RDBMS
No scripts or cronjobs to maintain
Supported by Oracle
Can switch between primary/standby repeatedly
Redo sent and applied continuously (options)
Standby db can be used for other things
Read-only when not applying redo logs
Read-write with limitations (Logical Standby)
Failover
Primary fails, standby becomes primary
Can’t switch back without rebuild

10. DataGuard Classic* Primary Database Standby Database Online Redo Logs
*Before choice of physical or logical standby
Standby mounted, recovering or
Standby read-only, no apply
Primary
Database
Standby
Database
Can switch back and forth
-Primary becomes standby
-Standby becomes primary
Online Redo
Logs
DataGuard
Archived
Redo Logs
Archived
Redo Logs

11. Applying Redo Logs Default Standby Redo Logs (Optional)
Archived redo log complete on primary
Sent and applied to standby
Standby Redo Logs (Optional)
Redo sent to standby as it is written on primary
Real-time apply
No waiting for primary archive redo log complete
No waiting for primary log switch
Not to be confused with init.ora parameter
VALID_FOR=(STANDBY_LOGFILES,…)

12. Standby Redo Logs Primary Database Standby Database Online Redo Logs
Primary redo written continuously to standby
No waiting for primary log switch
Primary
Database
Standby
Database
Online Redo
Logs
Archived
Redo Logs
DataGuard
Archived
Redo Logs
Standby
Redo Logs

13. Typical Configurations
Standby dedicated for failover
Primary db
configured for log switch every 15 minutes
Standby db
always applying redo logs
Behind primary by 15 minutes at most
Less if primary writes redo logs more often
Use standby redo logs
Very close to primary at all times

14. Typical Configurations
Standby for failover and reporting
Primary db
configured for log switch every 15 minutes
Standby db
apply redo logs 8pm to 5am
Long enough to apply 24 hours of redo logs
Stop applying redo logs 5am to 8pm
Standby up to 15 hours behind primary
Open for reporting 15 hours a day
Reports use ‘old’ data
Standby data doesn’t change from 5am to 8pm

15. Protection Modes Maximum Performance (default) Maximum Protection
Primary sends transactions to standby
Doesn’t wait for them to commit
Maximum Protection
Primary stops if standby doesn’t commit
Requires standby redo logs
Maximum Availability
Max protection but primary doesn’t stop
Switch to max perf until standby catches up
Switch back to max availability

16. DataGuard Physical Standby
Can’t change standby db objects
Log Apply
Services
Physical
Standby
Database
Primary
Database
Standby mounted, recovering Or
Standby read-only, no apply
Can switch back and forth
Online Redo
Logs
Archived
Redo Logs
DataGuard
Log Transport
Services
Archived
Redo Logs

17. Physical Standby a Standby?
Failover
Ready to failover?
Block by block copy of primary
If any changes made, can’t failover
Standby had to be opened resetlogs to change
Refresh
No questions
Complete rebuild from primary
Only need backup of primary, nothing else

18. Physical Standby Just a copy of production Only needed in production
Don’t need to do any dev, testing
Don’t need backups
Recover from backups of primary database
What is added to your infrastructure?
One database
No backups

19. Physical vs Logical Standby
Physical Standby
‘classic’ standby
Can’t connect to db while applying redo logs
Can be read only when not applying redo logs
Logical Standby
Applies redo logs from primary all the time
As long as SQL apply process is running
Open for users for read and write
Various restrictions
Many configuration options

20. DataGuard Logical Standby
Can change db objects (restrictions)
SQL Apply
Services
Logical
Standby
Database
Primary
Database
Standby open while redo applied
Online Redo
Logs
Online Redo
Logs
Archived
Redo Logs
Archived
Redo Logs
Two sets of archived
redo logs
DataGuard
Log Transport
Services
Archived
Redo Logs

21. DataGuard Logical Standby
Database
Primary
Database
SQL applied to Logical Standby
Just like any other database user
Online Redo
Logs
DataGuard
LogMiner
Extract SQL
Archived
Redo Logs
Archived
Redo Logs

22. Logical Standby Standby is open, read-write
Anything copied from primary
Maintained by DataGuard
Depending on Guard status
DataGuard doesn’t maintain things added to standby
Guard status restricts who can update
This can be bypassed
Alter session or database
Needed to import db objects into standby

23. Logical Standby Guard Status
All
SYS can modify anything in standby database
Standby
SYS can modify anything
Other users can modify objects not maintained by DataGuard
Subject to normal user privs
None
Standby not protected by DataGuard
Any user can alter db objects

24. Skipping Schemas, tables, transactions Why anything skipped?
May be skipped automatically
Can be skipped manually
Why anything skipped?
Performance
Unsupported db objects
More later

25. Logical Standby a Standby?
Failover
Ready to failover?
Not sure if standby is a complete copy
Tables, schemas, transactions skipped?
Standby can be changed
Failover not prevented
Changes can be made
No warning that changes made
Who knows what you are failing over to?

26. Logical Standby a Standby?
Refresh
Additional db objects in standby need backup
Refresh from primary wipes out these objects
Complete rebuild from primary
Insert additional db objects
If standby fails
Need to recover standby db from backups
Extract additional db objects from standby
Refresh logical standby

27. Refresh Standby Physical Standby Logical Standby Just refresh
Standard process
No debate
Logical Standby
Refresh wipes out unique db objects
Must extract them first
Refresh from primary
Load unique db objects

28. Standby Fails Physical Logical Logical standby db must be backed up
No problem, just a copy of primary
Refresh from primary
Logical
What about unique db objects
Recover standby from standby backups
Extract unique db objects
Refresh standby
Insert unique db objects
Logical standby db must be backed up

29. Recovering Logical Standby
You wanted Logical
To add things
Indexes for reporting
How to recover Logical?
Rebuild physical from primary
Convert to logical
How to recreate the additional db objects/data?
If indexes, recreate them
If data extracted from copy of primary?

30. How It Works Basic DataGuard setup Where to send archived redo logs?
Log_archive_dest_n
Where n is 1 to 10
Specific value doesn’t matter
Basic DataGuard setup
Where to send archived redo logs?
Primary
Log_archive_dest_1
Location for local archived redo logs
Location=/arch01/NY Valid_for=(All_Logfiles, All_Roles)
Log_archive_dest_2
Sends archived redo logs to service name
Service name points to standby
Service=LA Valid_for=(Online_logfiles, Primary_Role)
Tnsnames.ora
Contains entry for service name for standby

31. How it works Standby Log_archive_dest_1 Log_archive_dest_2
Log_archive_dest_n
Where n is 1 to 10
Specific value doesn’t matter
Standby
Log_archive_dest_1
Location for local archived redo logs
Not used while db is physical standby
Location=/arch01/LA Valid_for=(All_Logfiles, All_Roles)
Log_archive_dest_2
Location receives archived redo logs from primary
Location=/arch02/LA Valid_for=(Standby_logfiles, Standby_Role)

32. Symmetrical init.ora/spfile
Use three log_archive_dest_n parameters
Setup on primary and standby
Don’t need to change for failover
Don’t need to change for fail-back
Create tnsnames.ora entry
On primary
Pointing to standby
On standby
Pointing to primary
Less maintenance for frequent failover/back

33. DataGuard init.ora/spfile
Active
Inactive
Active
Inactive
Active for Logical Standby
Db_unique_name=NY_DB
Db_unique_name=LA_DB
Primary
Database
Standby
Database
Log_archive_dest_1
LOCATION=/arch01/NY
VALID_FOR=(ALL_LOGFILES,
ALL_ROLES)
Log_archive_dest_1
LOCATION=/arch01/LA
VALID_FOR=(ALL_LOGFILES,
ALL_ROLES)
Log_archive_dest_2
LOCATION=/arch02/NY
VALID_FOR=(STANDBY_LOGFILES,
STANDBY_ROLE)
Log_archive_dest_2
LOCATION=/arch02/LA
VALID_FOR=(STANDBY_LOGFILES,
STANDBY_ROLE)
Online Redo
Logs
Log_archive_dest_3
SERVICE=LA
VALID_FOR=(ONLINE_LOGFILES,
PRIMARY_ROLE)
Log_archive_dest_3
SERVICE=NY
VALID_FOR=(ONLINE_LOGFILES,
PRIMARY_ROLE)
Archived
Redo Logs
Archived
Redo Logs
Tnsnames.ora
LA=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)
(HOST=<hostnameLA>)(PORT=1521)) (CONNECT_DATA= (SID=LA_DB) ) )
Tnsnames.ora
NY=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)
(HOST=<hostnameNY>)(PORT=1521)) (CONNECT_DATA= (SID=NY_DB) ) )

34. DataGuard init.ora/spfile
Active
Inactive
Active for Logical Standby
Active
Inactive
Db_unique_name=NY
Db_unique_name=LA
Standby
Database
Primary
Database
Log_archive_dest_1
LOCATION=/arch01/NY
VALID_FOR=(ALL_LOGFILES,
ALL_ROLES)
Log_archive_dest_1
LOCATION=/arch01/LA
VALID_FOR=(ALL_LOGFILES,
ALL_ROLES)
Log_archive_dest_2
LOCATION=/arch02/NY
VALID_FOR=(STANDBY_LOGFILES,
STANDBY_ROLE)
Log_archive_dest_2
LOCATION=/arch02/LA
VALID_FOR=(STANDBY_LOGFILES,
STANDBY_ROLE)
Online Redo
Logs
Log_archive_dest_3
SERVICE=LA
VALID_FOR=(ONLINE_LOGFILES,
PRIMARY_ROLE)
Log_archive_dest_3
SERVICE=NY
VALID_FOR=(ONLINE_LOGFILES,
PRIMARY_ROLE)
Archived
Redo Logs
Tnsnames.ora
LA=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)
(HOST=<hostnameLA>)(PORT=1521)) (CONNECT_DATA= (SID=LA_DB) ) )
Tnsnames.ora
NY=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)
(HOST=<hostnameNY>)(PORT=1521)) (CONNECT_DATA= (SID=NY_DB) ) )
Archived
Redo Logs

35. DataGuard Reporting Logical Standby Database Primary Database
Database objects
Copied from primary
Maintained by DataGuard
Database objects added to
Logical standby database
-- indexes for reporting
Online Redo
Logs
DataGuard
LogMiner
Extract SQL
Archived
Redo Logs
Archived
Redo Logs

36. Rebuild Reporting Standby
If additional standby db objects have no data
Indexes for reporting
Refresh from primary wipes out indexes
Refresh standby
Execute script to recreate indexes

37. Create DataGuard Standby
Physical Standby
Logical Standby
Create physical standby
Convert to logical standby

38. Create Physical Standby
On Primary database
Enable Forced Logging
Create password file
Setup init.ora/spfile parameters
Verify archiving enabled
Backup db (hot or cold)
Create standby control file
Don’t use backup control file

39. Create Physical Standby
On Standby database
Copy db backup files from primary
Copy standby control file from primary
Setup init.ora/spfile parameters
Db_name same as primary db_name
Start physical standby db
Verify physical standby working

40. Convert to Logical Standby
On Primary database
Build LogMiner dictionary
On Standby database
Stop redo apply
Convert database to logical standby
Change db_name
Restart db
Open resetlogs
Verify logical standby working

41. Cascaded Standbys DataGuard supports cascading standbys
Primary sends redo to
Physical standby A
Logical standby B
Physical standby A sends redo to
Physical standby B
Physical standby C
Logical standby B sends redo to
Don’t you have enough to worry about?

42. Real World Example What I’m supporting now Requirements
Logical standby
2 added schemas for custom app
Primary db supports Oracle Applications 11i
Requirements
Provide copy of primary 11i db for reporting
Oracle Discoverer
Provide copy of tables for custom app
Additional schemas store custom app data
Extracted from standby copies of primary tables

43. DataGuard Logical Real World
Standby
Database
Primary
Database
Database objects
Copied from primary
Maintained by DataGuard
Database objects added to
Logical standby database
-- 2 schemas for custom app
-- store data extracted from standby copies of primary tables
Processed Data
Stored
Procs extract data
Online Redo
Logs
DataGuard
LogMiner
Extract SQL
Archived
Redo Logs
Archived
Redo Logs

44. Real World Refresh/Recovery
Backup standby db objects not in primary
Refresh standby from primary
Recreate additional db objects in standby
If Logical standby fails
Db objects not in primary are lost
Need to recover standby db
Extract db objects

45. Logical Standby Issues
Does this sound like a standby?
Unsupported
Data types
BFILE, user-defined types
PL/SQL supplied packages
That modify metadata, DBMA_JAVA etc.
Other things, see manual
If unsupported, automatically skipped
No notification of skipped objects
Examine primary for unsupported things

46. Logical Standby Issues
Does this sound like a standby?
Processing
Everything done on primary has to be extracted from redo logs and applied to standby db
Apply process is just another db user session
Primary db
Objects may not be well designed
Tables with poor (or no) indexes
Updates on primary can be very slow when applied as SQL to standby

47. Logical Standby Issues
Does this sound like a standby?
If applying to standby too slow
May have to skip for performance
To keep standby in synch per business reqmts
Ready for reporting once per day
Primary SQL depends on files on primary
Create java class
Class files not on standby
DataGuard doesn’t maintain filesystems
No notification of such problems

48. Logical Standby Issues
Performance impact
At any time, slow SQL may take days to complete
If you need standby in synch once per day
Must skip table
If you must have this table in standby
Must do full refresh from primary
If you can and do skip the table
Can’t support requirement for reporting on standby
You never know when this will happen

49. Logical Standby Issues
Logical Standby is like an application
Needs control, review, careful release process
If Logical Standby is an ‘application’
Need dev, alpha, beta, prod
Logical standby database for dev, alpha, beta
Backups for additional dbs
Add space to primary production database?
Need to add space to 4 primary, 4 logical dbs
What is added to your infrastructure?
4 standby databases
Backups for 4 standby databases
Does this sound like a standby?

50. Logical Standby Issues
How can standby get out of synch?
Someone bypassed guard and left it off
Someone left guard altered to NONE
SYS altered db objects in standby
Schema, table, transaction skipped
No record of transactions skipped
No utilities
Compare logical standby to primary
Compare tables standby/primary
Does this sound like a standby?

51. Logical Standby Issues
Logical apply process examines standby
When applying update from primary to standby
Compares
Previous values on primary
Current values on standby
If different, refuses to apply update from primary
Apply process fails
Can’t apply anything more
must cure issue or skip table/transaction
Differences can go undetected indefinitely
Until next time primary updates object
Does this sound like a standby?

52. Logical Standby Issues
Does this sound like a standby?
Need backups of logical standby database
If there are any unique database objects
If there aren’t, why use logical standby?
Refresh or rebuild
Have to recover db objects unique to standby
After refresh
Previously skipped tables
Do we skip them again?
Do we wait for them to need to be skipped?

53. Real World Redesign Primary Database Physical Standby Database
Separate database dedicated to custom application
Primary
Database
-- 2 schemas for custom app
-- store data extracted from tables in physical standby database
Physical
Standby
Database
Online Redo
Logs
Processed Data
Stored
Procs extract data
DataGuard
Archived
Redo Logs
Archived
Redo Logs

54. Real World Redesign Custom Application database
Dedicated for app schemas
Db link into physical standby
Backup provides recovery of app schemas
Physical Standby database
Let DataGuard do what it does well
None of the Logical Standby issues
Can be used as read-only for reporting
When not applying redo logs
Support an extra database
Don’t have to support Logical Standby

55. Recommendation Logical for reporting Objects added to standby
Copy of primary
Add indexes to speed reporting
Add tables for aggregates
Objects added to standby
Easily recreated from a SQL script
Contain data that can always be regenerated from copy of primary

56. Recommendation Physical standby Logical standby Is solid, dependable
No issues
Logical standby
Is it really a standby?
Is it ready for failover?
Is it providing complete data for reports?
Lots of issues
Is it worth the effort/risk?

57. DataGuard Support Issues
Covered in 2nd presentation
“Oracle DataGuard Logical Standby Support Issues”