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Database indexing: a simple explanation

When you search for a specific chapter in a book, you will most likely look at its table of contents. This allows you to quickly find the right page, instead of scrolling through all the pages one by one. Database indexing works the same way. Indexes are tools that help databases find data faster by minimizing search time. Let's look at what indexing is, how it works, and why it's so important for performance.

What is indexing?

Indexing is the process of creating a special data structure (index) that speeds up the search for information in a database. The index can be compared to the table of contents of a book or an index in a dictionary. It contains links to data organized in a specific way so that it can be found quickly.

For example, if you have a Users table with millions of records, and you need to find a user by name, without an index, the database will look through each row one by one. This is called a full table scan and can take a long time. With the index, the database immediately jumps to the desired entry, as if you had opened a book on the right page using the table of contents.

Imagine that you are reading an encyclopedia consisting of 1000 pages. If you need to find an article about "dinosaurs", you can:

Without a table of contents: scroll through each page until you find the desired article. This will take a long time, especially if the article is near the end of the book.

With the table of contents: open the table of contents, find the word "dinosaurs" and immediately go to the specified page.

Indexing in databases works the same way. Without an index, the database performs a complete search of all records. With an index, it uses a structured list (index) to quickly find the data you need.

How are indexes created?

Indexes are created based on one or more columns of a table. For example, if you frequently search for users by email, you can create an index for the email column. The database creates a special data structure (for example, a B-tree or hash table) that organizes column values in a specific order.

The database uses an index to quickly find the record with the specified email address, instead of checking every row.

How does this affect the speed of requests?

Speeding up the search

Indexes significantly reduce the time it takes to complete queries. Instead of a complete search, the database uses an index to find the necessary data immediately. This is especially important for large tables where the number of records is in the millions.

Optimization of filtering and sorting

Indexes also speed up filtering (WHERE) and sorting (ORDER BY) operations. For example, if you have an index on the date column, queries related to date sorting will run faster.

Reducing server load

Fast queries mean less load on the database server. This is especially important for highly loaded systems such as online stores or social networks.

Indexing Restrictions

Despite all the advantages, indexes have their drawbacks.:

They take up space

Indexes require additional disk space because they store copies of data in a special structure.

Slowing down write operations

Indexes should also be updated when data is added, modified, or deleted. This can slow down the INSERT, UPDATE, and DELETE operations.

They are not always effective

Indexes are only useful for frequent queries. If data is rarely requested, creating an index may be redundant.

When should I use indexes?

For frequently used columns

Create indexes on columns that are often used in queries (for example, WHERE, JOIN, ORDER BY).

For unique values

Indexes are especially useful for columns with unique values, such as email or ID.

For large tables

The more data in the table, the more useful the indexes are.

Database indexing is a powerful tool that helps speed up query execution, especially in large and complex systems. It works like the table of contents of a book, allowing the database to quickly find the necessary data, instead of going through all the records. However, it is important to remember that indexes have their limitations, such as increasing the time for write operations and using additional space.

Choosing the right indexes depends on the structure of your database and the nature of the queries. If you use indexes correctly, you can significantly improve the performance of your application. After all, as with a book, success depends not only on the amount of information, but also on how quickly you can find it!

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Кирилл Коваленко

Feb. 28, 2025 12:37

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