MySQL performance issue comparing 2 DateTime fields on the same table -


my feed_listingjob has 2 datetime fields:

+------------+-------------+------+-----+---------+----------------+ | field      | type        | null | key | default |          | +------------+-------------+------+-----+---------+----------------+ | id         | int(11)     | no   | pri | null    | auto_increment | | data       | longtext    | no   |     | null    |                | | meta_data  | longtext    | no   |     | null    |                | | state      | varchar(25) | no   |     | null    |                | | error      | longtext    | no   |     | null    |                | | job_id     | int(11)     | no   | mul | null    |                | | created_at | datetime(6) | no   | mul | null    |                | | updated_at | datetime(6) | no   | mul | null    |                | | es_sync_at | datetime(6) | yes  | mul | null    |                | +------------+-------------+------+-----+---------+----------------+

updated_at , es_sync_at both indexed individually below: 

mysql> show indexes feed_listingjob; +-----------------+------------+--------------------------------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | table           | non_unique | key_name                                                     | seq_in_index | column_name | collation | cardinality | sub_part | packed | null | index_type | comment | index_comment | +-----------------+------------+--------------------------------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | feed_listingjob |          0 | primary                                                      |            1 | id          |         |       64534 |     null | null   |      | btree      |         |               | | feed_listingjob |          1 | feed_listingjob_job_id_4c3b1b514481f269_fk_feed_importjob_id |            1 | job_id      |         |        2081 |     null | null   |      | btree      |         |               | | feed_listingjob |          1 | feed_listingjob_fde81f11                                     |            1 | created_at  |         |       64534 |     null | null   |      | btree      |         |               | | feed_listingjob |          1 | feed_listingjob_afd1a1a8                                     |            1 | updated_at  |         |       64534 |     null | null   |      | btree      |         |               | | feed_listingjob |          1 | feed_listingjob_381895a2                                     |            1 | es_sync_at  |         |           2 |     null | null   | yes  | btree      |         |               | +-----------------+------------+--------------------------------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 5 rows in set (0.00 sec)

and query not using indexes:

mysql> explain select `feed_listingjob`.`id` `feed_listingjob` `feed_listingjob`.`es_sync_at` < `feed_listingjob`.`updated_at` limit 10; +----+-------------+-----------------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table           | type | possible_keys | key  | key_len | ref  | rows  |       | +----+-------------+-----------------+------+---------------+------+---------+------+-------+-------------+ |  1 | simple      | feed_listingjob |  | null          | null | null    | null | 53534 | using | +----+-------------+-----------------+------+---------------+------+---------+------+-------+-------------+ 1 row in set (0.01 sec)

can please tell me why , how optimise query?

the index can't used here because feed_listingjob.updated_at not constant. means every row have examined check condition. 1 way use index have column stores difference between es_sync_at , updated_at timestamps. if store difference = (es_sync_at - updated_at timestamps) query becomes (difference < 0).


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