DBA Interview Questions

Here are some DBA interview questions.

• What are the dictionary tables used to monitor a database spaces? - DBA_FREE_SPACE DBA_SEGMENTS DBA_DATA_FILES.

• What are the roles and user accounts created automatically with the database? - DBA - role Contains all database system privileges. SYS user account - The DBA role will be assigned to this account. All of the base tables and views for the database’s dictionary are store in this schema and are manipulated only by ORACLE. SYSTEM user account - It has all the system privileges for the database and additional tables and views that display administrative information and internal tables and views used by oracle tools are created using this username. 

• What are the minimum parameters that should exist in the parameter file (init.ora)? - DB NAME - Must set to a text string of no more than 8 characters and it will be stored inside the datafiles, redo log files and control files and control file while database creation. DB_DOMAIN - It is string that specifies the network domain where the database is created. The global database name is identified by setting these parameters (DB_NAME & DB_DOMAIN) CONTORL FILES - List of control filenames of the database. If name is not mentioned then default name will be used. DB_BLOCK_BUFFERS - To determine the no of buffers in the buffer cache in SGA. PROCESSES - To determine number of operating system processes that can be connected to ORACLE concurrently. The value should be 5 (background process) and additional 1 for each user. ROLLBACK_SEGMENTS - List of rollback segments an ORACLE instance acquires at database startup. Also optionally LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and LICENSE_MAX_USERS.

• How can we specify the Archived log file name format and destination? - By setting the following values in init.ora file. LOG_ARCHIVE_FORMAT = arch %S/s/T/tarc (%S - Log sequence number and is zero left padded, %s - Log sequence number not padded. %T - Thread number left-zero- padded and %t - Thread number not padded). The file name created is arch 0001 are if %S is used. LOG_ARCHIVE_DEST = path. 

• What is user Account in Oracle database? - An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges.

• What is dynamic data replication? - Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem. 

• What is Two-Phase Commit? - Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase. 

• How can you Enforce Referential Integrity in snapshots? - Time the references to occur when master tables are not in use. Peform the reference manually, immdiately locking the master tables. We can join tables in snopshots by creating a complex snapshots that will based on the master tables. 

• What is a SQL * NET? - SQL *NET is ORACLE’s mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases. It is used in Clint-Server and Server-Server communications. 

• What is a SNAPSHOT? - Snapshots are read-only copies of a master table located on a remote node which is periodically refreshed to reflect changes made to the master table. 

• What is the mechanism provided by ORACLE for table replication? - Snapshots and SNAPSHOT LOGs 

• What is snapshots? - Snapshot is an object used to dynamically replicate data between distribute database at specified time intervals. In ver 7.0 they are read only.

• What are the various type of snapshots? - Simple and Complex. 

• Describe two phases of Two-phase commit? - Prepare phase - The global coordinator (initiating node) ask a participants to prepare (to promise to commit or rollback the transaction, even if there is a failure) Commit - Phase - If all participants respond to the coordinator that they are prepared, the coordinator asks all nodes to commit the transaction, if all participants cannot prepare, the coordinator asks all nodes to roll back the transaction. 

• What are the benefits of distributed options in databases? - Database on other servers can be updated and those transactions can be grouped together with others in a logical unit. Database uses a two phase commit. 

• What are the options available to refresh snapshots? - COMPLETE - Tables are completely regenerated using the snapshots query and the master tables every time the snapshot referenced. FAST - If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables. FORCE - Default value. If possible it performs a FAST refresh; Otherwise it will perform a complete refresh.

• What is a SNAPSHOT LOG? - A snapshot log is a table in the master database that is associated with the master table. ORACLE uses a snapshot log to track the rows that have been updated in the master table. Snapshot logs are used in updating the snapshots based on the master table. 

• What is Distributed database? - A distributed database is a network of databases managed by multiple database servers that appears to a user as single logical database. The data of all databases in the distributed database can be simultaneously accessed and modified. 

• How can we reduce the network traffic? - Replication of data in distributed environment. - Using snapshots to replicate data. - Using remote procedure calls.

• Differentiate simple and complex, snapshots? - A simple snapshot is based on a query thaat does not contains GROUP BY clauses, CONNECT BY clauses, JOINs, sub-query or snapshot of operations. - A complex snapshots contain at least any one of the above. 

• What are the Built-ins used for sending Parameters to forms? - You can pass parameter values to a form when an application executes the call_form, New_form, Open_form or Run_product. 

• Can you have more than one content canvas view attached with a window? - Yes. Each window you create must have at least one content canvas view assigned to it. You can also create a window that has manipulated content canvas view. At run time only one of the content canvas views assign to a window is displayed at a time.