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MySQL Internals Manual

23.16.3 Creating Index Keys

As part of every table-write operation (INSERT, UPDATE, DELETE), the storage engine is required to update its internal index information.

The method used to update indexes will vary from storage engine to storage engine, depending on the method used to store the index.

In general, the storage engine will have to use row information passed in methods such as [custom-engine.html#custom-engine-api-reference-write_row write_row()], [custom-engine.html#custom-engine-api-reference-delete_row delete_row()], and [custom-engine.html#custom-engine-api-reference-update_row update_row()] in combination with index information for the table to determine what index data needs to be modified, and make the needed changes.

The method of associating an index with its row will depend on your storage approach. Current storage engines store the row offset.