What is the Difference Between Indexing and Hashing? with Proper Definition and Brief Explanation

The main difference between indexing and hashing is that the indexing optimizes the performance of a database by reducing the number of disk accesses to process queries, whereas hashing computes the direct location of a data record on disk without use the index structure.

A database is a collection of associated data. A database management system or DBMS makes it easy to create and manage data in databases. Users can write SQL queries to perform operations on tables in a database. DBMS allows multiple users to access and use data. In addition, it allows transactions and provides data protection. Indexing and hashing are two concepts related to DBMS.

Key Areas Covered

1. What is indexing?
     – Definition, Functionality
2. What is the hash?
    – Definition, Functionality
3. What is the difference between indexing and hashing?
     – Comparison of key differences

Key terms

DBMS, clustered indexing, hash, indexing, ordered indexing, primary indexing, secondary indexing, SQL

What is indexing?

When executing SQL queries, it takes some time to access the data on disk. Here, an index is a data structure that helps to find and access data in a database table quickly. The indexing technique reduces the number of disks accessed to process queries.

An index consists of two sections; a search key and a data reference. The lookup key contains the primary key or candidate key of the table. The data reference contains the address of the disk block that has the value corresponding to that key.

In addition, there are several types of indexes. Some of them are the following.

Ordered indexing – Indexes are ordered, making searching for data faster.

Primary indexing – When the index is based on the primary key of the table, it is called a primary index. There are two types of indexes on the primary key called the dense and spare index. The dense index contains an index record for each lookup key value in the data file. In the spare index, there are index records for some data items.

Clustered Indexing – Uses a combination of two or more columns to create an index. A record group consists of records with the same characteristics. And, these groups create the indexes.

Secondary indexing – Contains another level of indexing to minimize the size of the mapping.

what is hash

In a large database, it is not possible to search all indexes to get the required data. Hashing helps find the direct location of a specific data record on disk without using indexing. Here, data blocks, also called data groups, store data. A hashing function is a mathematical function. It helps generate the addresses of those data blocks. Also, the hashing function can select any column value to generate the address, but it usually uses the primary key to generate the data block address.

There are two types of hash as static and dynamic hash. In the static hash, the address of the resulting data group is always the same. However, the static hash causes the bucket to overflow. Dynamic hashing is a solution to this problem. In dynamic hash, the data pool increases or decreases based on the number of records.

Difference Between Indexing and Hashing

Definition

Indexing is a data structure technique to efficiently retrieve records from database files based on some attributes on which indexing was performed. On the other hand, hashing is an effective technique for calculating the direct location of a data record on disk without using the index structure. Thus, this is the main difference between indexing and hashing. 

Functionality

Indexing uses the data reference that contains the address of the disk block with the value corresponding to the key, while hashing uses mathematical functions called hash functions to compute direct locations of data records on disk. Therefore, this is also an important difference between indexing and hashing.

Application

Another difference between indexing and hashing is that hashing works well for large databases than indexing.

Conclusion

The main difference between indexing and hashing is that indexing optimizes the performance of a database by reducing the number of disk accesses to process queries, whereas hashing computes the direct location of a data record on disk without use the index structure.

Reference:

1.“DBMS Indexing in DBMS – Javapoint”. www.javatpoint.com, available here.
2. “DBMS Hashing – Javatpoint.” www.javatpoint.com, available here.

Courtesy image:

1. “Hash table 4 1 1 0 0 1 0 LL” By Jorge Stolfi – Own work (Public Domain) via Commons Wikimedia

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