Why is My MySQL Query on a Large Table So Slow, and How Can I Optimize It?

MySQL Query Optimization for Large Table with Slow Execution Time

Your MySQL query is taking over a minute to execute because it lacks an efficient index to optimize the retrieval of data. The table's huge size, particularly over 1 million records, exacerbates the problem.

Indexing the table on the id column is crucial for speeding up queries that involve sorting by id. However, based on the provided information, it appears that indexing alone isn't sufficient.

Here are some suggestions to improve query performance:

Use a Range Query with WHERE Clause

Instead of using LIMIT to retrieve a specific range of records, consider utilizing a WHERE clause with relational operators. For instance, the following query uses a range query to select records with id values greater than or equal to 499501 and limits the result to 500 rows:

select * from `ratings` where id >= 499501 limit 500;

This query should perform significantly faster because it leverages the indexed id column to efficiently locate the desired records.

Explain the Query Plan

To further troubleshoot the issue, execute an EXPLAIN query to gain insights into the query execution plan. This will provide details about the query's type, the indexes utilized, and the estimated number of rows to be scanned.

explain select * from `ratings` where id >= 499501 limit 500;

Rule Out Deadlocks

Deadlocks occur when two or more concurrent transactions wait for each other to release locks, effectively preventing either from proceeding. While the provided information doesn't suggest deadlock as a possible cause, it's worth considering.

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