Real Time Oracle DBA Interview Questions and Answers - 1
Why do you mean PGA?
PGA is a memory area used by Oracle database. It is required to store session specific information.
What is the physical structure of the disk resources in Oracle?
Following is the physical structure of the disk resources in Oracle.
Control files – stores the status of the physical structure of the database. It contains different types of information, such as archive log history, data files records, redo threads, log records, and database name.
Data files – Refers to the physical files of the operating system that store the data of all logical structures in the database.
Redo log files – Refers to the files, which log a history of all changes made to the database.
What is the process of updating or inserting certain data in the database?
Following is the process to update or insert data in the database:
- RDBMS searches for parsed statement in library cache or parses the statement to generate execution plan.
- Server process retrieves relevant data from disk to the buffer cache.
- In case of inserting data in the database, the data block with sufficient free space will be retrieved.
- Lock is acquired. The data block is updated in the buffer cache.
- A lock is acquired on rollback segment as well to store old version of data in case rollback is required.
- User process creates a redo entry in the redo log buffer to support recovery.
How do you control the number of data files in an Oracle database?
The number of data files in an Oracle database is controlled by the initialization parameters DB_Files.
How do you determine the maximum number of data files in an Oracle database?
DB_Files initialization parameter determines the maximum number of data files. A change in this parameter requires the restart of the database.
The default value of DB_Files is operating system specific.
When determining a value for DB_Files, you should consider the following situations.
If the value of DB_Files is too low, you cannot and data files beyond the DB_Files limits without first shutting down the database.
If the value of DB_Files is too high, memory is unnecessarily consumed.
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