How Can I Efficiently Delete Millions of Rows in MySQL Without Impacting System Availability?

Deleting Millions of Rows in MySQL Without System Disruption

Handling the removal of a large number of duplicate rows can present challenges in maintaining system availability. In the referenced scenario, the MySQL table contains millions of unnecessary records, posing a significant hurdle.

To address this issue, one approach that avoids table locking is executing multiple smaller delete queries in a loop. This allows other operations to proceed concurrently, reducing the load on the database. However, this method can still impact performance and take an extended time to complete.

Alternatively, renaming the table and recreating an empty version can provide a more reliable solution. While it may involve more steps, this approach ensures data integrity and minimal interruption to users. After cleaning up the renamed table, it can be renamed back while the new, empty table is dropped. The merged rows can then be added to the renamed table.

However, a more efficient solution is to utilize a chunked deletion strategy. This approach uses a LIMIT clause to delete rows in smaller batches. By repeating this process in a loop with a brief pause between iterations, the database can effectively handle the deletion without causing significant disruptions:

<code class="sql">DELETE FROM `table`
WHERE (whatever criteria)
ORDER BY `id`
LIMIT 1000;</code>

This method allows for continuous deletion while ensuring minimal impact on system performance. Regular iterations to check for affected rows can indicate the completion of the process. As mentioned earlier, implementing this approach in a script with controlled pauses between iterations provides optimal performance and user experience.

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