Prepare 4 interview - Recent questions tagged database

Tell me about the Greenplum Architecture

Fri, 15 Jul 2011 07:17:42 +0000

How to create and use Greenplum External tables?

Fri, 15 Jul 2011 06:45:06 +0000

What is the difference between external tables and web tables of Greenplum database?

Fri, 15 Jul 2011 06:23:37 +0000

What is external tables and web tables in Greenplum database?

Fri, 15 Jul 2011 06:21:06 +0000

What is Greenplum database?

Fri, 15 Jul 2011 06:09:45 +0000

What is a Database Server?

Thu, 22 Jul 2010 20:50:52 +0000

What is the difference between DELETE and TRUNCATE?

Thu, 24 Jun 2010 12:27:15 +0000

What are different types of joins in SQL, in MS SQL Server?

Thu, 24 Jun 2010 10:20:51 +0000

What is Cascade and Restrict in DROP table SQL, in MS SQL Server?

Thu, 24 Jun 2010 10:04:08 +0000

Can we have a different collation for database and table?

Wed, 23 Jun 2010 13:37:39 +0000

In which files does actually SQL Server store data?

Wed, 23 Jun 2010 13:35:39 +0000

What are page splits?

Wed, 23 Jun 2010 13:35:18 +0000

What are the different sections in Page?

Wed, 23 Jun 2010 13:35:01 +0000

What is Extent and Page?

Wed, 23 Jun 2010 13:34:43 +0000

Have you heard about sixth normal form?

Wed, 23 Jun 2010 13:34:27 +0000

Can you explain Fifth Normal Form?

Wed, 23 Jun 2010 13:33:57 +0000

Can you explain Fourth Normal Form?

Wed, 23 Jun 2010 13:33:39 +0000

What is denormalization?

Wed, 23 Jun 2010 13:33:10 +0000

What is normalization? What are different types of normalization?

Wed, 23 Jun 2010 13:32:48 +0000

How many types of relationship exist in database designing?

Wed, 23 Jun 2010 13:31:17 +0000

What are E-R diagrams?

Wed, 23 Jun 2010 13:30:42 +0000

What is the difference between SQL SERVER 2000 and 2005?

Wed, 23 Jun 2010 13:30:25 +0000

What is SQL Server 2000 Workload Governor?

Wed, 23 Jun 2010 13:30:08 +0000

What is SQL SERVER Express 2005 Edition?

Wed, 23 Jun 2010 13:29:51 +0000

What is the difference between MSDE and SQL SERVER 2000?

Wed, 23 Jun 2010 13:29:30 +0000

Is access database a RDBMS?

Wed, 23 Jun 2010 13:29:03 +0000

What are CODD rules?

Wed, 23 Jun 2010 13:28:25 +0000

What is difference between DBMS and RDBMS?

Wed, 23 Jun 2010 13:27:49 +0000

What is ACID?

Tue, 22 Jun 2010 19:32:57 +0000

The ACID model is one of the oldest and most important concepts of database theory.

1) Atomicity states that database modifications must follow an “all or nothing” rule. Each transaction is said to be “atomic.” If one part of the transaction fails, the entire transaction fails.

2) Consistency states that only valid data will be written to the database. If, for some reason, a transaction is executed that violates the database’s consistency rules, the entire transaction will be rolled back and the database will be restored to a state consistent with those rules.

3) Isolation requires that multiple transactions occurring at the same time not impact each other’s execution.

4) Durability ensures that any transaction committed to the database will not be lost.

What is the difference between scope_identity() and @@identity

Tue, 22 Jun 2010 19:27:47 +0000

@@IDENTITY returns the most recently created identity for your current connection, not necessarily the identity for the recently added row in a table. You could have a situation where there is a trigger that inserts a new record in a Logs Table, for example, when your Stored Procedure or INSERT SQL Statement inserts a record in the Orders Table. If you use @@IDENTITY to retrieve the identity of the new order, you will actually get the identity of the record added into the Log Table and not the Orders Table, which will create a nasty, nasty bug in your data access layer.

To avoid the potential problems associated with someone adding a trigger later on, always use SCOPE_IDENTITY() to return the identity of the recently added row in your INSERT SQL Statement or Stored Procedure.

Tell me about Oracle Archiver (ARCn)

Mon, 21 Jun 2010 18:18:11 +0000

* Optional background process
* Automatically archives online redo log files when ARCHIVELOG mode is set
* Preserves the record of all changes made to the database

Tell me about System Monitor (SMON)

Mon, 21 Jun 2010 18:17:08 +0000

Responsibilities:
  * Instance recovery
        - Rolls forward changes in online redo log files
        - Opens database for user access
        - Rolls back uncommitted transactions
  * Coalesces free space
  * Deallocates temporary segments

Few words about Checkpoint (CKPT)

Mon, 21 Jun 2010 18:09:49 +0000

Responsible for:
    * Signaling DBWn at checkpoints
    * Updating datafile headers with checkpoint information
    * Updating control files with checkpoint information

What is Process Monitor (PMON)?

Mon, 21 Jun 2010 18:08:49 +0000

Cleans up after failed processes by:
        * Rolling back the transaction
        * Releasing locks
        * Releasing other resources
        * Restarting dead dispactchers

Tell me about Oracle Log Writer (LGWR)

Mon, 21 Jun 2010 18:08:00 +0000

LGWR writes:
     * At commit
     * When one-third full
     * When there is 1 MB of redo
     * Every three seconds
     * Before DBWn writes

Tell me about Oracle Database Writer (DBWn)

Mon, 21 Jun 2010 18:06:33 +0000

DBWn writes when:
    * Checkpoint occurs
    * Dirty buffers reach threshold
    * There are no free buffers
    * Timeout occurs
    * Tablespace OFFLINE
    * Tablespace READ ONLY
    * Table DROP or TRUNCATE
    * Tablespace BEGIN BACKUP

Tell me about Oracle Background Processes

Mon, 21 Jun 2010 18:05:15 +0000

Maintains and enforces relationships between physical and memory structures
Mandatory background processes:
DBWn, LGWR, PMON, CKPT, SMON

Optional background processes:
ARCn , LMDn, QMNn, CJQ0, LMON, RECO, Dnnn, LMS, Snnn, LCKn, Pnnn

Tell me about Oracle Server Process

Mon, 21 Jun 2010 18:02:37 +0000

* A program that directly interacts with the Oracle server
* Fulfills calls generated and returns results
* Can be dedicated or shared server

Tell me about Oracle User Process

Mon, 21 Jun 2010 18:02:00 +0000

* A program that requests interaction with the Oracle server
* Must first establish a connection
* Does not interact directly with the Oracle server

Tell me about Oracle "Process" Structure

Mon, 21 Jun 2010 18:01:05 +0000

Oracle takes advantage of various types of Processes:
* User Process: Started at the time a database user requests connection to the Oracle Server
* Server Process: Connects to the Oracle instance and is started when a user establishes a session
* Background Processes: Started when an Oracle instance is started

What is Java Pool?

Mon, 21 Jun 2010 17:53:27 +0000

* Services parsing requirements for Java commands
* Required if installing and using Java
* Sized by JAVA_POOL_SIZE parameter

What is Large Pool?

Mon, 21 Jun 2010 17:52:50 +0000

* An optional area of memory in the SGA
* Relieves the burden place on the Shared Pool
* Used for:
     - Session memory for the Shared Server
     - I/O server processes
     - Backup and restore operations for RMAN
* Does not use an LRU list
* Sized by LARGE_POOL_SIZE
* Can be dynamically resized

What is "Redo Log Buffer"?

Mon, 21 Jun 2010 17:50:33 +0000

*Records all changes made to the database data blocks
*Primary purpose is recovery
*Changes recorded within are called redo entries
*Redo entries contain information to reconstruct or redo changes
*Size defined by LOG_BUFFER

What is Database Buffer Cache?

Mon, 21 Jun 2010 17:49:52 +0000

*Stores copies of data blocks that have been retrieved from the data files
*Enables great performance gains when you insert and update data
*Managed through an LRU algorithm
*DB_BLOCK_SIZE determines primary block size

What is Data Dictionary Cache?

Mon, 21 Jun 2010 17:49:09 +0000

*A collection of the most recently used definitions in the database
*Includes information about database files, tables, indexes, columns, users, privileges, and other database objects
*During the parse phase, the server process looks at the data dictionary for information to resolve object names and validate access

What is Library Cache?

Mon, 21 Jun 2010 17:48:15 +0000

*Stores information about the most recently used SQL and PL/SQL statements
*Enables the sharing of commonly used statements
*Is managed by a least recently used (LRU) algorithm
*Consists of two structures
- Shared SQL area
- Shared PL/SQL area
*Size is determined by the Shared Pool sizing

What is Shared Pool?

Mon, 21 Jun 2010 17:46:54 +0000

*Used to store:
Most recently executed SQL statements
Most recently used data definitions

*It consists of two key performance-related memory structures:
Library Cache
Data Dictionary Cache

*Sized by the parameter SHARED_POOL_SIZE

What is "System Global Area"?

Mon, 21 Jun 2010 17:45:46 +0000

*The SGA consists of several memory structures:
Shared Pool
Database Buffer Cache
Redo Log Buffer
Other structures

*There are two additional memory structures that can be configured within the SGA:
Large Pool
Java Pool

*The size of the SGA is determined by the parameters that set the sizes of the various pools; these parameters are dynamic

*The SGA_MAX_SIZE parameter sets the maximum size of the SGA (so you can limit it) and is not a dynamic parameter

Tell me about "Memory Structure of Oracle"

Mon, 21 Jun 2010 17:44:39 +0000

Oracle’s memory structure consists of two memory areas known as:

1.System Global Area (SGA): Allocated at instance start up, and is a fundamental component of an Oracle Instance
2.Program Global Area (PGA): Allocated when the server process is started

Few words about "Basic Oracle Architecture"

Mon, 21 Jun 2010 17:42:29 +0000

Technically an Oracle Database is broken into two high-level components

1.INSTANCE – Non-persistent, memory-based processes and structures
2.DATABASE – Persistent, disk-based data and control files

An Oracle Instance…
Is a means to access an Oracle Database
Always opens one and only one Database
Consists of memory and background process structures