When a query tries to modify database, original data entries are kept in separate location and then changes are applied to datafiles. The data kept in separate location is called Undo data. Undo data is used to maintain data integrity and data consistency.Oracle uses Undo data in following situations Continue reading “Undo Management and Undo Tablespace | Undo Retention”
Oracle has provided powerful mechanism to protect database in situation of data loss. This mechanism includes a range of methods to Backup and Recover your data. First step is to backup you data and second step is to recover required data. Broadly speaking, oracle supports two types of backups, Logical Backup and Physical database backups.
This article explains configuration of oracle Database 10g as shared server. Before reading this article you must have concept of Oracle shared server and dedicated server architecture. Visit following link to revive shared server and dedicated server architecture.
Configuration of shared server involves only few steps. Oracle database 10g has pre-configured setting to enable shared server. Shared server can be configured by setting values for few initialization parameters at run time. These parameters can also be initialized in initialization parameter file. Following section discusses these parameters in detail. Continue reading “Configuration of Oracle Shared Server”
In order to communicate with oracle database, oracle users need a program such as SQL *Plus which can issue SQL statements and few processes which can execute these SQL statements. These processes are divided into User Process, Server Process and Background Processes. User process runs user application like SQL *Plus. Server process manages oracle user process’s requests. Server process executes SQL statements and returns result to user process. Background processes are the core of oracle database which handle over all database operations. Continue reading “Oracle Shared Server and Oracle Dedicated Server Architecture”
Oracle server requires some metadata information to process SQL statements. This information is necessary to maintain data integrity, data consistency and data security. When a user submits a query, oracle needs detailed information about objects involved in the query, for example, whether the accessed objects exist and the user has required privileges. Continue reading “Oracle Dictionary Cache | Oracle Data Dictionary”
Library cache is very important part of Oracle Shared pool. Shared Pool controls execution of SQL statements. Shared pool is divided into Data dictionary Cache and Library Cache. Main component of Library cache include Shared SQL Area and Private SQL Area (in case of shared server configuration).In Dedicated server configuration Private SQL area is created in PGA of server process. In oracle database each statement is associated with a shared area and a private area. Both are discussed in detail below.
Oracle database keeps record of changes made to data. Every time user performs a DML, DDL or DCL operation, its redo entries are also created. These redo entries contain commands to rebuild or redo the changes. These entries are stored in Redo Log buffer. Log writer process (LGWR) writes these redo entries to redo log files. Redo log buffer works in circular fashion. It means that it overwrites old entries. Continue reading “Redo Log Buffer & Log writer process (LGWR)”