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Oracle DataGuard Concepts and Architecture

Oracle DataGuard Concepts and Architecture. Brian Hitchcock OCP 10g DBA Sun Microsystems brian.hitchcock@sun.com brhora@aol.com. www.brianhitchcock.net. Brian Hitchcock October 23, 2007. Page 1. Oracle DataGuard. Maintains a standby database Archived redo logs on primary

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Oracle DataGuard Concepts and Architecture

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  1. Oracle DataGuardConcepts and Architecture Brian HitchcockOCP 10g DBA Sun Microsystems brian.hitchcock@sun.com brhora@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 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 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* *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 doesn’t change from 5am to 8pm

  15. Protection Modes • Maximum Performance (default) • 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 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 • 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 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 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 Active Inactive Active for Logical Standby Inactive 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 Tnsnames.ora LA=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp) (HOST=<hostnameLA>)(PORT=1521)) (CONNECT_DATA= (SID=LA_DB) ) ) Archived Redo Logs Tnsnames.ora NY=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp) (HOST=<hostnameNY>)(PORT=1521)) (CONNECT_DATA= (SID=NY_DB) ) )

  34. DataGuard init.ora/spfile Active Active Active for Logical Standby Inactive 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 • 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 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?

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