/    /  DBMS – Indexing



Indexing is used to optimise the performance of a database system.

It reduces the required number of disk accesses to a minimum when a query is executed.


There are 4 types of Indexing methods:

  1. Ordered Indices
  2. Primary Index
  3. Clustering Index
  4. Secondary Index


An index for a file in a database system works in the same way as the index in a textbook.


The index record contains two parts :


  • Search-key value
  • Pointer


Here, the search-key value is the input and the pointer is the output.


For a given search-key value the database system looks for the record, to which the pointer indicates.


Indices are categorized in two ways:


  1. Ordered Indices: Based on a sorted ordering of the values.


  1. Hash Indices: Based on a uniform distribution of values across a range of buckets.


The bucket to which a value is assigned is determined by a function, called a ‘hash function’.

A file may have several indices, based on the different search keys.


An index entry consists of a search-key value and the pointers to one or more records with that value as their search-key value.


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