SQL Server Architecture Interview Questions and Answers
What is RAID and what are different types of RAID configurations?
RAID stands for Redundant Array of Independent Disks. RAID defines data storage schemes to divide and replicate data among various disks so that data reliability and I/O performance can be increased.
The basic configurations of RAID are:
LEVEL 0 : Striped set without parity/Non-Redundant Array
LEVEL 1 : Mirrored set without parity
LEVEL 2 : Redundancy through Hamming code
LEVEL 3 : Striped set with dedicated parity/Bit interleaved parity
LEVEL 4 : Block level parity
LEVEL 5 : Striped set with distributed parity
LEVEL 6 : Striped set with dual distributed Parity
What is database architecture?
Database architecture describes the design of the database. It explains how the data is stored. The data of the server is stored in databases. This database is further split into one or more discs. The database can be considered to have two layers. Physical layer, which is a transparent layer for the database administrators to work on. Other users typically work on the user view layer. Tables, views, procedures forms this view
What are pages and Extents?
A page is a unit of data storage in SQL. The size of a page is 8Kb. A page has a header and a body. Different types of pages are: Date, text, index , page free space etc. The data rows are put on the page serially after the header.
Extents are units in which space is allocated to tables and indexes. An extent is 8 continuous pages. SQL Server has two types of extents: uniform and mixed extent. For efficient allocation, the SQL server does not allocate whole extents to tables with small amounts of data
What do you know about system database?
The system database contains information/metadata for all database present on an SQL Server instance. The system database stores information regarding logins, configuration settings, connected servers etc. It also holds various extended stored procedures to access external processes and applications.
Major system databases :
Master: Core system database to mange Sql Server instance.
Resource: Responsible for physically storing all system objects.
TempDB: This is a temporary database used to store temporary, tables, cursors, indexes, variables etc.
Model: This acts as a template database for all user created databases.
MSDB: Database to manage SQL Server agent configurations.
Distribution: Database primarily used for SQL Server replication.
ReportServer: Main database for reporting services to store metadata and other object definitions.
ReportServerTempDB: Acts as a temporary storage for reporting services.
What are Page Splits?
When there is not enough room on a page for a new row, a Server splits the page, allocates a new page, and moves some rows to the new page