Limit/Offset Pagination vs. Cursor Pagination in MySQL

Pagination in MySQL

Pagination is an essential technique in managing and displaying large datasets in a manageable and user-friendly way. Its primary function is to divide extensive result sets into smaller, discrete “pages” of data, which can be loaded and displayed progressively to enhance user experience and performance.

Importance of Pagination

Enhancing User Experience

In web applications, users do not want to scroll through long, unmanageable lists. Pagination allows users to navigate through data systematically, presenting them with a subset of data at a time, which is more digestible and easier to manage.

Managing Large Datasets

Handling large datasets efficiently is critical for performance. Without pagination, queries may return thousands or millions of rows, which can overwhelm both the client side and the database server. Pagination helps by limiting the number of rows retrieved in each query iteration, thus improving the performance and responsiveness of applications.

Common Pagination Methods

There are primarily two methods for paginating data in a MySQL database:

• Limit/Offset Pagination: This is the more traditional form of pagination, where SQL queries use the LIMIT clause to specify the number of records to fetch and use the OFFSET to specify the starting point.
• Cursor Pagination: Cursor pagination, also known as “keyset pagination,” involves using a reference point (cursor) to fetch rows following or preceding the given cursor. This method is generally more efficient for large datasets.

Limit/Offset Pagination

Implementation

The LIMIT and OFFSET clauses are used in SQL queries to control the result set. The LIMIT specifies the maximum number of rows to return, and the OFFSET specifies how many rows to skip before beginning to return rows.

Using LIMIT Clause

Here’s a basic example of using the LIMIT clause:

SELECT * FROM books ORDER BY published_at DESC LIMIT 10;

This query fetches the first 10 rows from the books table ordered by publication date.

To fetch the next page, you use the OFFSET clause:

SELECT * FROM books ORDER BY published_at DESC LIMIT 10 OFFSET 10;

This returns rows 11 through 20.

Another approach supported by MySQL is combining the two in a single LIMIT clause:

SELECT * FROM books ORDER BY published_at DESC LIMIT 10, 10;

This also fetches rows 11 through 20.

Avoiding High OFFSET Values

One significant drawback of the LIMIT/OFFSET approach is performance degradation with higher OFFSET values. The database must skip rows to reach the specified offset, which can be costly for large datasets. An effective way to mitigate this is by using indexed columns in the WHERE clause:

SELECT * FROM books WHERE id > 1000 ORDER BY id ASC LIMIT 10;

Here, id should be an indexed column, making the pagination more efficient.

Advantages and Disadvantages

Simplicity and Ease of Use

The LIMIT/OFFSET method is straightforward and easy to implement. It doesn’t require maintaining the state of previous queries.

Performance Issues

However, as mentioned, using high OFFSET values results in performance issues, as the database needs to scan and discard the skipped rows. This method can become inefficient for very large datasets.

Cursor Pagination

Implementation

Cursor-based pagination uses a cursor to keep track of the last-seen item and fetches rows based on this cursor. This method is often more efficient for large datasets.

Using Cursors

Here’s a simple example of cursor-based pagination:

SELECT * FROM books WHERE id > 1000 ORDER BY id ASC LIMIT 10;

Assume the last row in the previous result set had an id of 1009; to fetch the subsequent rows:

SELECT * FROM books WHERE id > 1009 ORDER BY id ASC LIMIT 10;

Another way to use cursors is by leveraging the ROW_NUMBER() window function:

SELECT * FROM (
    SELECT id, title, published_at, ROW_NUMBER() OVER (ORDER BY id) as row_num FROM books
) as temp_table
WHERE row_num > 1000 AND row_num <= 1010;

Efficient Data Retrieval

Cursor pagination can be more performant because it doesn’t need to skip rows like LIMIT/OFFSET. Instead, it uses an indexed column directly to fetch the necessary rows.

Advantages and Disadvantages

Performance Benefits

Cursor pagination often results in better performance, especially with very large datasets, since it avoids the inefficiencies associated with high OFFSET values.

Complexity in Implementation

The downside is that cursor pagination is more complex to implement and manage, as it requires maintaining the state (i.e., the cursor) between queries. This method can also be less flexible than LIMIT/OFFSET for certain use cases.

Summary

Both LIMIT/OFFSET and cursor pagination are essential techniques for handling large datasets in MySQL efficiently. Each has its use cases, advantages, and disadvantages.

• Limit/Offset Pagination: Simple to implement and works well for relatively small datasets. Becomes inefficient with high offsets due to the need to skip rows.
• Cursor Pagination: More efficient for large datasets, especially when high offsets are needed. However, it requires more careful implementation and state management.

Selecting the appropriate pagination method depends largely on the specific requirements of the application, the size of the dataset, and the performance characteristics required. By understanding these methods, developers can ensure efficient data retrieval and improved application performance, thereby providing a better user experience.

TiDB supports both limit/offset and cursor-based pagination techniques, similar to MySQL. Given TiDB’s distributed nature, cursor pagination can be particularly advantageous as it more efficiently handles large datasets spread across multiple nodes by reducing the need to skip rows. Moreover, its support for keyset pagination helps in maintaining optimal performance by leveraging the distributed indexing capabilities.