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User-Managed Incomplete Recovery Copyright © Oracle Corporation, 2002. All rights reserved. Objectives After completing this lesson, you should be able to do the following: • Describe the steps of incomplete recovery • Perform an incomplete database recovery • Identify the loss of current online redo log files 14-2 Copyright © Oracle Corporation, 2002. All rights reserved. Incomplete Recovery Overview User process User process Instance SGA Shared pool Server process PGA Server process Large Pool Shared SQL and PL/SQL Data buffer Redo log buffer Data dict. cache SMON DBWn PMON CKPT LGWR ARCn PGA Parameter file Password file 14-3 Locks 1 1 1 Datafile 1 Control Redo log files file 1 1 0 Redo log Datafile 2 file 2 1 Datafile 3 Database Copyright © Oracle Corporation, 2002. All rights reserved. Archived log files Situations Requiring Incomplete Recovery • • • Complete recovery fails because an archived log is lost. All unarchived redo log files and a datafile are lost. User error – An important table was dropped. – Invalid data was committed in a table. • 14-4 Current control file is lost and a backup control file must be used to open the database. Copyright © Oracle Corporation, 2002. All rights reserved. Types of Incomplete Recovery • There are three types of incomplete recovery: – Time-based recovery – Cancel-based recovery – Change-based recovery • You may need to recover using a restored control file when: – Control files are lost – Performing incomplete recovery to a point when the database structure is different than the current 14-5 Copyright © Oracle Corporation, 2002. All rights reserved. Incomplete Recovery Guidelines • • • • 14-7 Follow all steps carefully. Take whole database backups before and after recovery. Always verify that the recovery was successful. Back up and remove archived logs. Copyright © Oracle Corporation, 2002. All rights reserved. Incomplete Recovery and the Alert Log • • 14-9 Check the alert log before and after recovery Contains error information, hints, and SCNs Copyright © Oracle Corporation, 2002. All rights reserved. User-Managed Procedures for Incomplete Recovery 1. Shut down and back up the database. 2. Restore all datafiles. Do not restore the control file, redo logs, password file, or parameter file. 3. Mount the database. 4. Recover the datafiles to a point before the time of failure. 5. Open the database with RESETLOGS. 6. Perform a closed database backup. 14-10 Copyright © Oracle Corporation, 2002. All rights reserved. RECOVER Command Overview • Recover a database until cancel: RECOVER DATABASE until cancel • Recover a database until time: RECOVER DATABASE until time ‘2002-07-24:14:22:03’ • Recover using backup control file: RECOVER DATABASE until time ‘2002-07-24:14:22:03’ using backup controlfile 14-11 Copyright © Oracle Corporation, 2002. All rights reserved. Time-Based Recovery: Example Scenario: • The current time is 12:00 p.m. on March 9, 2002. • The EMPLOYEES table has been dropped. • • • 14-12 The table was dropped at approximately 11:45 a.m. Database activity is minimal because most staff are currently in a meeting. The table must be recovered. Copyright © Oracle Corporation, 2002. All rights reserved. UNTIL TIME Recovery 146 146 146 Datafile 1 Control Redo log File 1 Files 146 145 DatafileEMP 2 Redo log File 2 146 Datafile 3 1 2 Shut down and back up 3 Mount the database 144 146 146 Datafile 1 Control Redo log File 1 Files 144 145 Datafile EMP 2 Redo log File 2 144 Datafile 3 Database 1 1 1 Datafile 1 Control Redo log File 1 Files 1 0 DatafileEMP 2 Redo log File 2 1 Datafile 3 Recovered Database 14-13 Restore all datafiles Restored Database 5 Open with Resetlogs 6 Back up the database Copyright © Oracle Corporation, 2002. All rights reserved. 4 144 Archived log file Cancel-Based Recovery: Example Scenario: • The current time is 12:00 p.m. on March 9,2002. • The EMPLOYEES table was dropped while someone was trying to fix bad blocks. • Log files exist on the same disk. • The table was dropped at approximately 11:45 a.m. • Staff are currently in a meeting. 14-15 Copyright © Oracle Corporation, 2002. All rights reserved. Cancel-Based Recovery: Example Findings: • Redo logs are not multiplexed. • One of the online redo logs is missing. • The missing redo log is not archived. • The redo log contained information from 11:34 a.m. • Twenty-six minutes of data will be lost. • Users can recover their data. 14-16 Copyright © Oracle Corporation, 2002. All rights reserved. Using a Backup Control File During Recovery Scenario: • The current time is 12:00 p.m. on March 9, 2002. • The tablespace containing the EMPLOYEES table has been dropped. • The error occurred around 11:45 a.m. • Many employee records were updated this morning, but not since 11:00 a.m. • Backups are taken every night. 14-18 Copyright © Oracle Corporation, 2002. All rights reserved. Using a Backup Control File During Recovery Findings: • The backup from last night contains datafiles and control files that are required for recovery. • The EMP_TS tablespace has one datafile. • • • 14-19 The current log sequence number is 61. You confirm that the tablespace was dropped at 11:44:54 a.m. on March 9, 2002. Datafile number 4 is offline. Copyright © Oracle Corporation, 2002. All rights reserved. Loss of Current Redo Log Files If the database is closed: • Attempt to open the database. • Find the current log sequence number. • Recover the database using UNTIL CANCEL. 14-21 • • Drop and re-create log files if necessary. Open the database using RESETLOGS. • Perform a whole-database backup. Copyright © Oracle Corporation, 2002. All rights reserved. Summary In this lesson, you should have learned how to: • Perform incomplete database recovery • Recover from the loss of current online redo log files 14-23 Copyright © Oracle Corporation, 2002. All rights reserved. Practices 14-1 and 14-2 Overview These practices cover the following topics: • Recovery from user failure • Recovery with lost archived redo log files 14-24 Copyright © Oracle Corporation, 2002. All rights reserved.