Undo Management and Undo Tablespace | Undo Retention

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”

SQL Processing

When query is submitted to oracle server, various processing steps are performed to execute query. Following main steps are involved in this process.

1- Query Parsing

2- Optimizer determines most efficient way to execute query and generates an execution plan.

3- Finally SQL engine executes query.

In 1st step, SQL server checks syntax of query and outputs error if found.

After parsing of query, optimizer generates execution plan. Execution plan produced by optimizer depends on two main possible goals Continue reading “SQL Processing”