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Oracle DataGuard Concepts and Architecture Brian Hitchcock OCP 10g DBA Sun Microsystems [email protected] [email protected] www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 1 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 2 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 3 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 4 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 5 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 6 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 7 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 Archived Redo Logs Scripts, Cron Jobs Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 8 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 9 DataGuard Classic* *Before choice of physical or logical standby Primary Database Standby Database Standby mounted, recovering or Standby read-only, no apply Can switch back and forth -Primary becomes standby -Standby becomes primary Online Redo Logs Archived Redo Logs DataGuard Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 10 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,…) www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 11 Standby Redo Logs Primary Database Primary redo written continuously to standby No waiting for primary log switch Standby Database Online Redo Logs Archived Redo Logs Archived Redo Logs DataGuard Standby Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 12 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 13 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 14 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 15 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 Log Transport Services DataGuard Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 16 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 17 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 18 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 19 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 Log Transport Services DataGuard Archived Redo Logs Two sets of archived redo logs Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 20 DataGuard Logical Standby Logical Standby Database Primary Database SQL applied to Logical Standby Just like any other database user Online Redo Logs Archived Redo Logs DataGuard Archived Redo Logs LogMiner Extract SQL www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 21 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 22 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 23 Skipping Schemas, tables, transactions – – May be skipped automatically Can be skipped manually Why anything skipped? – – – Performance Unsupported db objects More later www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 24 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 25 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 26 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 27 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 28 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 29 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 30 How it works Standby – Log_archive_dest_n Where n is 1 to 10 Specific value doesn’t matter 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) www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 31 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 32 DataGuard init.ora/spfile Active Active Inactive Db_unique_name=NY_DB Primary Database Online Redo Logs Archived Redo Logs Inactive Db_unique_name=LA_DB 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) Log_archive_dest_3 SERVICE=LA VALID_FOR=(ONLINE_LOGFILES, PRIMARY_ROLE) Log_archive_dest_3 SERVICE=NY VALID_FOR=(ONLINE_LOGFILES, PRIMARY_ROLE) Tnsnames.ora LA=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp) (HOST=<hostnameLA>)(PORT=1521)) (CONNECT_DATA= (SID=LA_DB) ) ) Active for Logical Standby Tnsnames.ora NY=(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp) (HOST=<hostnameNY>)(PORT=1521)) (CONNECT_DATA= (SID=NY_DB) ) ) Standby Database Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 33 DataGuard init.ora/spfile Active Inactive Active for Logical Standby Db_unique_name=NY Standby Database Archived Redo Logs Active Inactive Db_unique_name=LA 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) Log_archive_dest_3 SERVICE=LA VALID_FOR=(ONLINE_LOGFILES, PRIMARY_ROLE) Log_archive_dest_3 SERVICE=NY VALID_FOR=(ONLINE_LOGFILES, PRIMARY_ROLE) 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) ) ) Primary Database Online Redo Logs Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 34 DataGuard Reporting Logical Standby Database Primary Database Database objects added to Logical standby database -- indexes for reporting Online Redo Logs Archived Redo Logs Database objects Copied from primary Maintained by DataGuard DataGuard Archived Redo Logs LogMiner Extract SQL www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 35 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 36 Create DataGuard Standby Physical Standby Logical Standby – – Create physical standby Convert to logical standby www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 37 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 38 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 39 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 40 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 41 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 42 DataGuard Logical Real World Primary Database Database objects added to Logical standby database -- 2 schemas for custom app -- store data extracted from standby copies of primary tables Logical Standby Database Database objects Copied from primary Maintained by DataGuard Procs extract data Online Redo Logs Archived Redo Logs DataGuard Archived Redo Logs Processed Data Stored LogMiner Extract SQL www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 43 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 44 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 45 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 46 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 47 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 48 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 49 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 50 Logical Standby Issues Logical apply process examines standby – – When applying update from primary to standby Compares Previous values on primary Current values on standby – – – Does this sound like a 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 51 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 52 Real World Redesign Separate database dedicated to custom application Primary Database Physical Standby Database -- 2 schemas for custom app -- store data extracted from tables in physical standby database Online Redo Logs Procs extract data Archived Redo Logs DataGuard Processed Data Stored Archived Redo Logs www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 53 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 54 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 www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 55 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? www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 56 DataGuard Support Issues Covered in 2nd presentation “Oracle DataGuard Logical Standby Support Issues” www.brianhitchcock.net Brian Hitchcock October 23, 2007 Page 57