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Oracle dba training
- 2. Relational Database Management System (RDBMS) RDBMS is based on the relational model. Data and relations are stored in the form of tables. Tables are accessed via Primary Keys, Foreign Keys and Indexes. RDBMS provides consistency which means transactions are either completed fully or no effect at all RDBMS provides concurrency which means multiple users accessing the same group of resources (such as tables, rows)
- 3. RDBMS & SQL Database Market Share is 40 % dominated by Oracle whereas IBM occupies 31%, Microsoft 12% and remaining by others. User interface with RDBMS in SQL – a standard interactive and programming language for querying and modifying data and managing databases.
- 4. Installing and upgrading Database software and application tools Allocating system storage and planning future allocation Creating Database and its storage parameters . Creating Database structures , objects, users and granting privileges DBA Tasks
- 5. DBA Tasks Set up Database security and auditing Set up Database Backup and Recovery when required Set up Database Monitoring Database Optimization and Performance Tuning Maintaining Database and implementing High Availability
- 10. What is an Oracle Instance ? An Oracle instance is a means to access the Oracle Database Always opens one and only one database What is SGA ? SGA is System Global Area . It constitutes DBBC ( Database Buffer Cache ), RBC(Redolog Buffer Cache) , Shared Pool and Shared Server. What is server process ? Services a single user process in the dedicated server and multiple user processes in a shared server. What is user process? Runs on a client machine using tools like SQL Plus , OEM etc. Significant Terms to be known
- 11. What is an Instance ? • An Instance is made up of background processes and memory structures . • An instance controls zero or more databases. • A database can have one or more instances. • Examples : PMON, SMON, DBWR, LOGWR etc..
- 12. Oracle Instance and Database Oracle Instance constitutes : Background Processes and Memory Structures Oracle Database constitutes : Data files Redo log files Control files Archive log files Parameter files
- 16. Background Processes Performs functions on behalf of user process Input, Output and Monitor other Oracle Processes to provide improved parallelism for better performance and reliability
- 17. Background Processes DBWR: When it writes into datafiles : When dirty buffer of the whole block reaches threshold limit When Checkpoint occurs When there are no free buffers Time out Occurs Tablespace is taken offline /read only/begin backup Drop/truncate a table
- 18. BGP Log Writer: Performs sequential writes from Redolog Buffer When LGWR writes: Commit When 1/3 of memory is full Every 3 seconds When it reaches 1 MB Before DBWR writes Calls on DBWR to write into data files Used for Recovery purposes
- 19. BGP SYSTEM MONITOR ( SMON ) Used for Instance Recovery (System/Media Failure ) Rollforward committed transactions (changes in redolog files) Open Database for access Rollback uncommitted transactions Coalesces free spaces Deallocates Temporary Segmen PROCESS MONITOR (PMON ) Cleans the failed process Rolls back user’s current transactions Releasing locks Releasing other resources Restoring dead dispatchers
- 20. BGP CheckPoint: Checkpoint is an event that occurs whenever the log switches Signals the DBWR to flush the data from DBBC to DF Updates SCN and LSN Stages of Redolog: Active – written over, ready to move to archive Inactive – ready to overwrite , information passed to archive Current – currently writing Unused - Freshly created group
- 21. BGP Members Status 1. Stale – Half-written and switched log 2. Blank - Currently Writing 3. delete - dropped members 4. invalid – corrupted, inaccessible
- 22. System Global Area (SGA) SGA is dynamic Allocated and tracked in granules by SGA Components Contiguous Virtual Memory Allocation A Granule is the unit of contiguous Memory Allocation DBBC and Shared Pool grow and Shrink
- 23. sga SGA_MAX_SIZE v$buffer_pool Fixed SGA – Shared Pool, DBBC ,RLBC Dynamic SGA – Changes made while DB is up DB_CACHE_SIZE LOG_BUFFER SHARED_POOL_SIZE LARGE_POOL_SIZE JAVA_POOL_SIZE
- 24. Shared Pool This is used for objects shared globally such as reusable execution plans, pl/sql packages, procedures, functions, cursor information etc., LRU Algorithm : As the Cache fills, less recently used execution plans and parse trees are removed from LC to make room for the new entries Shared Pool Contains : Library Cache and Data Dictionary Cache
- 25. Library Cache Stores information about the shared sql and pl/sql statements Enables the sharing of commonly used statements LRU Algorithm SharedSQL Shared PL/SQL Shared_pool_size Memory is allocated when a statement is parsed or a program unit is called
- 26. Shared SQL Stores and Shares the execution plan and parse trees for sql statements run against the database If second time an sql statement is run, it can take parse information already available is reused The text,schema and bind variables must be same to ensure that sql statements share the shared SQL Area Shared PL/SQL Stores and shares the most recently used pl/sql statements. Parsed and compiled programs with units and Procedures are stored in this area
- 27. Data Dictionary Cache Also called as Row Cache Most recently used data definitions in the Database Includes information about database files, users, privileges, tables, indexes, column and other database objects To resolve object names and validate access the server process looks at data dictionary Information about user data,data file names,segment names,extent location,table description