Top 50 Oracle Core Dba Interview Questions You Must Prepare 06.Jul.2022

Oracle database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.

A cluster with an index on the cluster key.

  • Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.
  • Hide data complexity.
  • Simplify commands for the user.
  • Present the data in a different perspective from that of the base table.
  • Store complex queries.

When an instance of an Oracle database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.

Only its owner can access a private synonym.

Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.

The set of redo log files for a database is collectively known as the database redo log.

The related columns of the tables in a cluster are called the cluster key.

Each index has an index segment that stores all of its data.

Private database link, public database link & network database link.

Schema objects are the logical structures that directly refer to the database's data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

A sequence generates a serial list of unique numbers for numerical columns of a database's tables.

The primary function of the redo log is to record all changes made to data.

Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

A synonym is an alias for a table, view, sequence or program unit.

Oracle database is comprised of three types of files. One or more datafiles, two are more redo log files, and one or more control files.

In circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs, the data for the row is stored in a chain of data block (one or more) reserved for that segment.

A database link is a named object that describes a "path" from one database to another.

Views do not contain or store data.

Database name - Names and locations of a database's files and redolog files. - Time stamp of database creation.

A segment is a set of extents allocated for a certain logical structure.

  • Take the tablespace or datafile to be recovered offline if the database is open.
  • Restore a backup of the datafiles you want to recover.
  • Apply online or archived redo logs, or a combination of the two.

A database contains one or more rollback segments to temporarily store "undo" information.

Because the database continues writing to the file during an online backup, there is the possibility of backing up inconsistent data within a block. For example, assume that either RMAN or an operating system utility reads the block while database writer is in the middle of updating the block. In this case, RMAN or the copy utility could read the old data in the top half of the block and the new data in the bottom top half of the block. The block is a fractured block, meaning that the data in this block is not consistent.

A schema is collection of database objects of a user.

Network database link is created and managed by a network domain service. A network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.

Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.

Temporary segments are created by Oracle when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.

To generate read-consistent database information during database recovery and to rollback uncommitted tractions by the users.

A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.

A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

Mask the real name and owner of an object. - Provide public access to an object - Provide location trparency for tables, views or program units of a remote database. - Simplify the SQL statements for database users.

Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner's views or procedures.

A data block size is specified for each Oracle database when the database is created. A database users and allocated free database space in Oracle data blocks. Block size is specified in init.ora file and cannot be changed latter.

A Consistent backup is one in which the files being backed up contain all changes upto the same system change number (SCN).

The information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database's data files.

There are two types of synonyms private and public.

  1. Mount the database
  2. Ensure that all datafiles you want to recover are online
  3. Restore a backup of the whole database or the files you want to recover
  4. Apply online or archived redo logs, or a combination of the two

An extent is a specific number of contiguous data blocks, obtained in a single allocation and used to store a specific type of information.

Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.

Data segment, index segment, rollback segment and temporary segment.