How to Optimize MySQL LIMIT Queries with Large Offsets?

Optimizing MySQL LIMIT Query with a Large Offset

LIMIT clause is commonly used to retrieve a subset of records from a MySQL table. However, when the offset value (m) becomes large, the query's performance can significantly deteriorate. This is because MySQL typically employs a sequential scan to traverse the entire table until it reaches the desired offset.

To alleviate this performance issue, consider creating an indexing table that establishes a sequential key corresponding to the primary key of your target table. This auxiliary table, known as the "indexing table," will act as a bridge between your target table and the desired rows.

By joining the indexing table to your target table, you can use a WHERE clause to efficiently retrieve the specific rows you need. Here's how to implement this approach:

1. Create the Indexing Table:

CREATE TABLE seq (
   seq_no int not null auto_increment,
   id int not null,
   primary key(seq_no),
   unique(id)
);

2. Populate the Indexing Table:

TRUNCATE seq;
INSERT INTO seq (id) SELECT id FROM mytable ORDER BY id;

3. Perform the Optimized Query:

To retrieve rows with offset 1,000,000 and a limit of 1000, execute the following query:

SELECT mytable.* 
FROM mytable 
INNER JOIN seq USING(id)
WHERE seq.seq_no BETWEEN 1000000 AND 1000999;

This optimized query leverages the indexing table to bypass the sequential scan and directly access the desired rows. As a result, the performance should be considerably improved, even with large offset values.

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