Oracle dataguard overview
- 1. Oracle10g Data Guard Overview
- 2. Objectives • Explain the benefits of Data Guard and why we might use it • Describe the basic components of Oracle Data Guard
- 3. Benefits of Oracle Data Guard • Configure the system to meet business protection and recovery requirements • Continuous service through a disaster or crippling data failure • Complete data protection against corruptions and data loss • Reduce overhead on primary systems by offloading: – adhoc queries – reporting – backups • Centralized management (Data Guard Broker, Data Guard Manager via Enterprise Manager)
- 4. Data Loss Causes… Hardware & System Error 44% Human Error 32% Software Corruption 14% Computer Viruses 7% Natural Disasters 3% * Protect Data 2006
- 5. What is Data Guard? Primary Standby Database Database Redo Oracle Net Database Database Copy Oracle® Data Guard Concepts and Administration 10g Release 2 (10.2) “Ch. 1 Introduction to Oracle Data Guard “
- 7. Standby Databases There are two types of standby databases: 1. Physical standby database 2. Logical standby database
- 8. Data Guard Services There are three types of services provided between the Primary and Standby databases: 1. Redo Transport: (2 types: Archival or Real-Time) • Controls the transfer of redo data from the primary database to the standby database. 2. Log Apply: (2 types: Redo Apply or SQL Apply) • Applies redo data on the standby database to maintain synchronization with the primary database. 3. Role Transitions: (2 types: Switchover or Failover) • Change the role of a database: SWITCHOVER: standby to primary + primary to standby FAILOVER: standby to primary
- 9. Data Guard Services Redo Transport Redo transport services perform the following tasks: • Transmits redo data from the primary to one or more standbys (9 max*) using ARCH or LGWR (LNSn) • Enforces the database protection mode • Automatically detects missing or corrupted archived redo log files on the standby and retrieves replacement archived redo log files from the primary, or another standby database i.e.: “GAP” RESOLUTION • Archival or Real-Time
- 10. Data Guard Services No Standby – No REDO Transport Primary Database Transactions LGWR Online Redo Log Files ARC0 Archived Redo Log Files
- 11. Data Guard Services Redo Transport (Archival) Primary Physical Database Standby Transactions Database LGWR RFS MSRP Archival Transport Online Redo Redo Log Files Apply ARC0 ARC1 ARC0 Archived Redo Log Files Archived Redo Log Files
- 12. Data Guard Services Redo Transport (Real-Time) Primary Logical Database Standby Transactions Database LGWR LSN0 RFS LGWR LSP Online Standby SQL Redo Log Files Redo Log Files Real-Time Apply Transport (Required) ARC0 ARC0 Archived Redo Log Files Archived Redo Log Files
- 13. Data Guard Services Redo Transport Configuration Redo transport is configured via parameters: LOG_ARCHIVE_DEST_n (n = { 1..10 }) • One destination must be LOCAL and must be MANDATORY. This destination, usually n = 1, is always archived first when using ARCH for redo transport • Destination n = 10 is the default FLASHBACK RECOVERY area. LOG_ARCHIVE_DEST_STATE_n • Allows one to ENABLE, DEFER, or RESET a specific destination STANDBY_ARCHIVE_DEST (standby only) • If no LOG_ARCHIVE_DEST_n locations specified then provides default location for archived redo logs
- 14. Data Guard Services Log Apply (Redo Apply) For physical standby databases, Data Guard uses Redo Apply technology, which applies redo data on the standby database using standard recovery techniques of an Oracle database. I.e. Block-for-block, byte-for-byte, bit-for-bit identical to primary.
- 15. Data Guard Services Log Apply (SQL Apply) For logical standby databases, Data Guard uses SQL Apply technology, which transforms the received redo data into SQL statements and then executes the generated SQL statements on the logical standby database. I.e. Use Log Mining to extract the redo, transform the redo into SQL statements, then execute the SQL statements against the logical standby.
- 16. Role Transitions Switchover and Failover • Not automatically invoked (but can be…) • Switchover – Planned role reversal – Used for OS or hardware maintenance • Failover – Unplanned role reversal – Use in an emergency – Minimal or zero data loss depending on choice of data protection mode
- 17. Data Protection Modes Maximum Protection • Ensures that no data loss will occur if the primary database fails. • Redo needed to recover each transaction must be written to both the local online redo log and to the standby redo log on at least one standby database before the transaction commits. • If a fault prevents the primary database from writing its redo stream to the standby redo log of at least one transactionally-consistent standby database, the primary database shuts down.
- 19. Data Protection Modes Maximum Performance • Default. Provides highest level of data protection possible without affecting the performance of the primary database. • Transactions may commit as soon as the redo data needed to recover them transaction is written to the primary’s online redo log. • Redo data stream written asynchronously to at least one standby database. • If sufficient bandwidth exists, provides a level of data protection that approaches that of maximum availability mode with minimal impact on primary database performance.
- 20. Setting the Protection Mode To set up redo transport services and specify a level of data protection for the Data Guard configuration, perform the following steps. Step 1: Configure the LOG_ARCHIVE_DEST_n parameters on the primary database. Maximum Maximum Maximum Protection Availability Performance Redo archival process LGWR LGWR LGWR or ARCH Network Transmission SYNC SYNC SYNC or ASYNC (LGWR) Mode SYNC (ARCH) Disk Write Option AFFIRM AFFIRM AFFIRM or NOAFFIRM Standby Redo Log Yes Yes No but recommended Required?
- 21. Setting the Protection Mode Step 1: Bounce the primary database: SQL> SHUTDOWN IMMEDIATE; SQL> STARTUP MOUNT; * If RAC, shutdown all instances, restart/mount one instance. Step 2: Set the mode: SQL> ALTER DATABASE SET STANDBY DATABASE TO PROTECTION MODE; Step 3: Open the Primary Database: SQL> ALTER DATABASE OPEN; Step 4: Confirm LOG_ARCHIVE_DEST_n parameter(s) on Standby Database: SQL> SHOW PARAMETER log_archive_dest_ Step 5: Confirm configuration: SQL> SELECT PROTECTION_MODE, PROTECTION_LEVEL FROM V$DATABASE;
- 22. Summary In this lesson you should have learned: • Benefits of Data Guard and why we might use it • Basic components of Oracle Data Guard