How do I optimize a query on a large MySQL table without any joins?
How can I optimize this single query from one large table (~ 75M rows)?
SELECT
log_id
FROM
score
WHERE
class_id IN (17,395)
ORDER BY date_reverse
LIMIT 10000;
I am pulling out the last 10k entries for a specific set of classes so that I can quickly find out if they already exist or not during a larger script import.
I think I have indexed appropriately, but this query takes 5 to 50 seconds!
Let me know if you need anything else.
EXPLAIN
SELECT
log_id
FROM
score
WHERE
class_id IN (17,395)
ORDER BY date_reverse
LIMIT 10000;
*** row 1 ***
table: score
type: range
possible_keys: class_id,score_multi_2,class_id_date_reverse,score_multi_5
key: class_id_date_reverse
key_len: 4
ref: NULL
rows: 1287726
Extra: Using where; Using index; Using filesort
CREATE TABLE `score` (
`log_id` bigint(20) NOT NULL,
`profile_id` bigint(20) DEFAULT NULL,
`date` datetime DEFAULT NULL,
`class_id` int(11) NOT NULL,
`score` float(10,6) DEFAULT NULL,
`score_date` datetime DEFAULT NULL,
`process_date` datetime DEFAULT NULL,
`status_type_id` int(3) NOT NULL DEFAULT '0',
`date_reverse` int(11) DEFAULT NULL,
UNIQUE KEY `unique_key` (`log_id`,`class_id`),
KEY `class_id` (`class_id`),
KEY `profile_id` (`profile_id`),
KEY `date` (`date`),
KEY `score` (`score`),
KEY `status_type_id` (`status_type_id `),
KEY `status_type_id_date` (`status_type_id`,`date`),
KEY `class_status_type_id_date_log_id` (`class_id`,`status_type_id`,`date`,`log_id`),
KEY `date_reverse` (`date_reverse`),
KEY `class_id_date_reverse` (`class_id`,`date_reverse`),
KEY `date` (`date`),
KEY `class_id_date_reverse_log_id` (`class_id`,`date_reverse`,`log_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
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1 answer
I guess the fastest way to run this query is to bite the bullet and allow sorting by 20,000 rows. I mean the following query:
SELECT *
FROM ((SELECT log_id
FROM score
WHERE class_id = 17
ORDER BY date_reverse
LIMIT 10000
) UNION ALL
(SELECT log_id
FROM score
WHERE class_id = 395
ORDER BY date_reverse
LIMIT 10000
)
) s
ORDER BY date_reverse
LIMIT 10000;
For this query, you want the merged index on score(class_id, date_reverse, log_id)
. Each subquery must use this index efficiently. However, the final sort will require you to use file sort.
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