Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 1 Chapter 1 Backup and Recovery Overview MSCD642 Backup and Recovery

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 2 Chapter Objectives Identify the files associated with an Oracle9i database List the logical structure of an Oracle9i database Identify the components of an Oracle9i instance

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 3 Chapter Objectives (Cont.) Identify the purpose of each background process of an Oracle instance Identify the purpose of each component of the system global area (SGA) Identify the purpose of the INIT.ORA file and the version available with the Oracle9i database

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 4 Chapter Objectives (Cont.) Define mean-time-between-failures (MTBF) and mean-time-to-recover (MTTR) Identify the parameters that can be used to speed up instance recovery Identify the various types of failures that can occur in an Oracle9i database

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 5 Chapter Objectives (Cont.) Use the Enterprise Manager Console to view the names and locations of the control file

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 6 Oracle9i Database Structures Database – consists of both a physical and logical structure –Physical structure – the physical operating system files –Logical structure – structures referenced and manipulated by the DBMS

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 7 Physical Structure Three types of database files: –Control file –Redo log file –Data file

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 8 Control File Small binary file containing: –name of database –location and name of all data and redo log files Recommended: two mirrored copies Minimum: one Maximum: eight Default: three

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 9 Redo Log File Contains committed transactions Changes must be written to a redo log file before updated to data files Two files are required, three is the default Written to in a circular fashion

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 10 Redo Log File Write Sequence

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 11 Data File Stores the actual database data Have the file extension.dbf DOES NOT correspond to an object name

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 12 Locating Database Files Location of file Physical and Logical Structures

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 13 Logical Structure Database - largest Tablespace Segment Extent Oracle9i data block – smallest

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 14 Tablespace Contains related objects: –Indexes –Table data Belongs to only one database Stored in one or more data files Composed of segments

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 15 Segment Four types: –Data segments: store table data –Index segments: store index data –Undo segments: store data for rollback operations –Temporary segments: store data for sort operations Consist of extents Can belong to only one tablespace at a time

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 16 Extent Consists of contiguous Oracle9i data blocks Add more extents to: –Increase size of segment; –Subsequently increases size of tablespace

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 17 Oracle9i Data Block Smallest storage unit that can be referenced by the DBMS Size specified during database creation Should be multiple of operating system block size Maximum size is operating system dependent

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 18 Relationship Between Physical and Logical Structures

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 19 Oracle9i Instance Consists of: –Background processes –Memory structures Started before the database files are opened

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 20 Background Processes System Monitor (SMON) – performs instance recovery Process Monitor (PMON) – “cleans up” failed user processes Log Writer (LGWR) – writes all changed data blocks from memory to the redo log files

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 21 Background Processes (Cont.) Database Writer (DBWn) – writes changed data blocks from memory to the actual data files Checkpoint (CKPT) – triggers writing of modified data Archiver (ARCn) – copies filled online redo log files after a log switch (optional process)

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 22 Memory Structures Program global area (PGA) –Contents vary based on database server configuration –Allocated when the server process is started –Deallocated when the server process ends System global area (SGA) – –Consists of several substructures –Allocated when the instance is started

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 23 System Global Area (SGA) Substructures SGA substructures include: –Shared pool library cache: holds most recently used SQL and PL/SQL statements data dictionary cache: holds database object information –Database buffer cache: contains most recently used data blocks –Redo log buffer: stores changes made to contents of the data files

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 24 Initialization File (INIT.ORA) Contains parameter values for starting the database Two versions: –Pfile Can be altered using a text editor Create from spfile using CREATE pfile FROM spfile; –Spfile Binary; generated by Oracle9i server Can be created from alter pfile using CREATE spfile FROM pfile;

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 25 Spfile Example

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 26 Backup and Recovery Terminology Backup – creating valid copies of database files Recovery – returning the database to a desired state

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 27 DBA Recovery Goals Mean-time-between-failures (MTBF) –Increase by performing preventive maintenance Mean-time-to-recover (MTTR) –Decrease with frequent backups and recovery preparation

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 28 Tuning Instance Recovery FAST_START_MTTR_TARGET parameter: –Maximum number of seconds worth of data writes that should be held in memory –Value range: 0 to 3600 seconds FAST_START_PARALLEL_ROLLBACK parameter: –Can enable parallel processes for SMON operations –Possible values: FALSE, HIGH, or LOW

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 29 Database Failure Two types: –Non-media failure Usually recoverable by background processes –Media failure Unable to access a database file Requires DBA intervention

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 30 Types of Non-Media Failures Process failure –Internal error or abnormal termination –Normally corrected by PMON Instance failure –Instance shuts down abruptly –Normally corrected by SMON

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 31 Types of Non-Media Failures (Cont.) Statement failure –Syntax error in submitted SQL or PL/SQL statement –Corrected by submitting valid statement User error –Data or tables are incorrectly altered –May require DBA intervention to correct error

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 32 Backup and Recovery Strategy Factors Determine the strategic importance of the database Develop a backup strategy based on availability concerns Recovery method depends on cause of database failure Always test (and practice) recovery methods

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 33 Chapter Summary An Oracle9i database is composed of three types of physical files: control, data, and redo log files Has both a physical and logical structure Oracle server consists of both a database and an instance An instance consists of background processes and memory structures

Chapter 1Oracle9i DBA II: Backup/Recovery and Network Administration 34 Chapter Summary (Cont.) Background process started by default: SMON, PMON, LGWR, DBWn, and CKPT Two primary memory areas: PGA and SGA INIT.ORA file consists of initialization parameters used during instance and database start-up Two types of failures: non-media and media