/DBMS_SQL_Overview

DBMS SQL Overview

DBMS 1

  • About DBMS
  • ER Diagram, Entity Set, Relationship, Cardinality Constraint, Attributes, Constraints
  • Keys
  • Functional Dependency
  • Decomposition of a Relation
  • Types of Decomposition

DBMS 2

  • Normalization
  • Transaction
  • Acid properties
  • Schedules
  • Relational Algebra

DBMS 3

  • SQL
  • DDL , DML , DCL
  • SQL queries

Deadlocks (Important):

A situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process. Deadlock can arise if following four conditions hold simultaneously (Necessary Conditions) :

  1. Mutual Exclusion – One or more than one resource is non-sharable (Only one process can use at a time).
  2. Hold and Wait – A process is holding at least one resource and waiting for resources.
  3. No Preemption – A resource cannot be taken from a process unless the process releases the resource.
  4. Circular Wait – A set of processes are waiting for each other in circular form.
  • Methods for handling deadlock: There are three ways to handle deadlock
  1. Deadlock prevention or avoidance : The idea is to not let the system into a deadlock state.
  2. Deadlock detection and recovery : Let deadlock occur, then do preemption to handle it once occurred.
  3. Ignore the problem all together : If deadlock is very rare, then let it happen and reboot the system. This is the approach that both Windows and UNIX take.