Technical Interview Questions and Answers :: Accenture
Tot. Mock Test: 6
Total Qs: 152+
A tablespace is a storage location where the actual data underlying database objects can be kept. It provides a layer of abstraction between physical and logical data and serves to allocate storage for all DBMS managed segments.
The SYSAUX tablespace is a new tablespace that is required in Oracle Database 10g. SYSAUX is a secondary tablespace for storage of a number of database components that were previously stored in the SYSTEM tablespace. It is created as a locally managed tablespace using automatic segment space management.
SYSTEM – a tablespace that is always used to store SYSTEM data that includes data about tables, indexes, sequences, and other objects – this metadata comprises the data dictionary. Every Oracle database has to have a SYSTEM tablespace—it is the first tablespace created when a database is created.
An Oracle database is comprised of one or more logical storage units called tablespaces. The database's data is collectively stored in the database's tablespaces. Each tablespace in an Oracle database is comprised of one or more operating system files called datafiles.
Database buffer cache is typically the largest portion of the SGA. It has data that comes from the files on disk. Because accessing data from disk is slower than from memory, the database buffer cache's sole purpose is to cache the data in memory for quicker access.
A log buffer is a circular buffer in the SGA that holds information about changes made to the database. This information is stored in the redo entries. Redo entries contain the information necessary to reconstruct or redo changes made to the database by insert, update, delete, create, alter, or drop operations. Redo entries are primarily used for database recovery as necessary.
The server processes generate redo data into the log buffer as they make changes to the data blocks in the buffer. LGWR subsequently writes entries from the redo log buffer to the online redo log.
The redo log buffer is a RAM area (defined by the initialization parameter log_buffer) that works to save changes to data, in case something fails and Oracle has to put it back into its original state (a ?rollback?). When Oracle SQL updates a table (a process called Data Manipulation Language, or DML), redo images are created and stored in the redo log buffer. Since RAM is faster than disk, this makes the storage of redo very fast.
No Discussion on this question yet!
Cold backup is a physical backup. During a cold backup, the database is closed and not available to users. All files of the database are copied (image copy). The data files do not change during the copy so the database is in sync upon restore.
Used when: Service level allows for some down time for backup
Hot backup is a physical backup. In a hot backup, the database remains open and available to users. All files of the database are copied (image copy). There may be changes to the database as the copy is made and so all log files of changes being made during the backup must be saved too. Upon a restore, the changes in the log files are reapplied to bring the database in sync.
Used when: A full backup of a database is needed Service level allows no down time for the backup
A cold backup also called an offline backup, is a database backup during which the database is offline and not accessible to update. This is the safest way to back up because it avoids the risk of copying data that may be in the process of being updated.
No Discussion on this question yet!