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Oracle DataGuard Concepts and Architecture

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Title: Oracle DataGuard Concepts and Architecture


1
Oracle DataGuardConcepts and Architecture
  • Brian HitchcockOCP 10g DBA
  • Sun Microsystems
  • brian.hitchcock_at_sun.com
  • brhora_at_aol.com

www.brianhitchcock.net
Brian Hitchcock October 23, 2007
Page 1
2
Oracle DataGuard
  • Maintains a standby database
  • 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
  • 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?
  • 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 doesnt 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 cant be used for anything else
  • Constantly recovering
  • Failover
  • Open standby db with resetlogs
  • Cant be standby again without rebuild
  • Cant fail back to primary without rebuild

8
Standby
Cant change standby db objects
Primary Database
Standby Database
Standby mounted, recovering Can only be opened
resetlogs Once opened, cant 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
  • Cant switch back without rebuild

10
DataGuard Classic
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
  • 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 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 doesnt change from 5am to 8pm

15
Protection Modes
  • Maximum Performance (default)
  • Primary sends transactions to standby
  • Doesnt wait for them to commit
  • Maximum Protection
  • Primary stops if standby doesnt commit
  • Requires standby redo logs
  • Maximum Availability
  • Max protection but primary doesnt stop
  • Switch to max perf until standby catches up
  • Switch back to max availability

16
DataGuard Physical Standby
Cant 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, cant 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
  • Dont need to do any dev, testing
  • Dont 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
  • Cant 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
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 doesnt 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
  • Subject to normal user privs

24
Skipping
  • Schemas, tables, transactions
  • 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
  • Insert additional db objects

27
Refresh Standby
  • Physical 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
  • 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
Log_archive_dest_n Where n is 1 to 10 Specific
value doesnt 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
  • ServiceLA Valid_for(Online_logfiles,
    Primary_Role)
  • Tnsnames.ora
  • Contains entry for service name for standby

31
How it works
Log_archive_dest_n Where n is 1 to 10 Specific
value doesnt 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
  • Dont need to change for failover
  • Dont 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
Active
Inactive
Active for Logical Standby
Inactive
Db_unique_nameNY_DB
Db_unique_nameLA_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 SERVICELA VALID_FOR(ONLINE_LO
GFILES, PRIMARY_ROLE)
Log_archive_dest_3 SERVICENY VALID_FOR(ONLINE_LO
GFILES, PRIMARY_ROLE)
Archived Redo Logs
Tnsnames.ora LA(DESCRIPTION (ADDRESS(PROTOCOL
tcp) (HOSTlthostnameLAgt)(PORT1521))
(CONNECT_DATA (SIDLA_DB) ) )
Archived Redo Logs
Tnsnames.ora NY(DESCRIPTION (ADDRESS(PROTOCOL
tcp) (HOSTlthostnameNYgt)(PORT1521))
(CONNECT_DATA (SIDNY_DB) ) )
34
DataGuard init.ora/spfile
Active
Active
Inactive
Active for Logical Standby
Inactive
Db_unique_nameNY
Db_unique_nameLA
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 SERVICELA VALID_FOR(ONLINE_LO
GFILES, PRIMARY_ROLE)
Log_archive_dest_3 SERVICENY VALID_FOR(ONLINE_LO
GFILES, PRIMARY_ROLE)
Archived Redo Logs
Tnsnames.ora LA(DESCRIPTION (ADDRESS(PROTOCOL
tcp) (HOSTlthostnameLAgt)(PORT1521))
(CONNECT_DATA (SIDLA_DB) ) )
Archived Redo Logs
Tnsnames.ora NY(DESCRIPTION (ADDRESS(PROTOCOL
tcp) (HOSTlthostnameNYgt)(PORT1521))
(CONNECT_DATA (SIDNY_DB) ) )
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
  • Dont 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
  • Dont you have enough to worry about?

42
Real World Example
  • What Im supporting now
  • 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 20-30 tables for custom app
  • Additional schemas store custom app data
  • Extracted from standby copies of primary tables

43
DataGuard Logical Real World
Logical 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
  • Refresh
  • 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
  • Refresh standby from primary
  • Recreate additional db objects in standby

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 doesnt 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
  • Cant 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
  • Cant 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 arent, 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
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
  • Dont have to support Logical Standby

55
Recommendation
  • Logical for reporting
  • 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
  • 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
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