The optimization process and recommendations:

1. Avoid Correlated Subqueries (query line: 7): A correlated subquery is a subquery that contains a reference (column: data_id) to a table that also appears in the outer query. Usually correlated queries can be rewritten with a join clause, which is the best practice. The database optimizer handles joins much better than correlated subqueries. Therefore, rephrasing the query with a join will allow the optimizer to use the most efficient execution plan for the query.
2. Avoid Selecting Unnecessary Columns (query line: 2): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
3. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.

Optimal indexes for this query:

ALTER TABLE `data_aud` ADD INDEX `data_aud_idx_data_id_rev` (`data_id`,`rev`);

The optimized query:

SELECT
        * 
    FROM
        data_aud publish_au0_ 
    WHERE
        data_au0_.rev = (
            SELECT
                max(data_au1_.rev) 
            FROM
                data_aud data_au1_ 
            WHERE
                data_au1_.rev <= 999999 
                AND data_au0_.data_id = data_au1_.data_id
        ) 
        AND data_au0_.data_id = 'my-data-01'