Share an example of mysql optimization
Today, database operations have increasingly become the performance bottleneck of the entire application, especially for Web applications. Regarding the performance of the database, this is not just something that DBAs need to worry about, but this is something that we programmers need to pay attention to. When we design the database table structure and operate the database (especially SQL statements when looking up tables), we need to pay attention to the performance of data operations. Here, we will not talk too much about the optimization of SQL statements, but only focus on MySQL, the database with the most Web applications. I hope the following optimization tips are useful to you.
1.Table structure
CREATE TABLE `room_break_history_tmp_test ` ( `id` INT(11) NOT NULL AUTO_INCREMENT, `break_type` INT(11) DEFAULT NULL, `app_id` INT(11) DEFAULT NULL, `room_id` INT(11) DEFAULT NULL, `from_user_id` INT(11) DEFAULT NULL, `to_user_id` INT(11) DEFAULT NULL, `content_type` INT(11) DEFAULT NULL, `content_name` VARCHAR(300) DEFAULT NULL, `source_message` VARCHAR(1536) DEFAULT NULL, `send_message` VARCHAR(1536) DEFAULT NULL, `request_type` INT(4) DEFAULT NULL, `report_relation` VARCHAR(1536) DEFAULT NULL, `handle_type` INT(11) DEFAULT NULL, `handle_uid` INT(11) DEFAULT NULL, `create_time` DATETIME DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_from_user_id` (`room_id`,`from_user_id`,`handle_type`,`create_time`) ) ENGINE=INNODB AUTO_INCREMENT=3416971 DEFAULT CHARSET=utf8mb4
2.Execution statement
DESC SELECT COUNT(1) FROM (SELECT COUNT(1) FROM room_break_history_tmp_test WHERE `create_time` BETWEEN '2017-07-01 22:25:33' AND '2017-07-01 22:27:00' AND handle_type = 5 GROUP BY room_id, from_user_id) AS keywordtemp
3 .Execution plan
id select_type table type possible_keys key key_len ref rows Extra ------ ----------- ------------------ ------ ---------------- ---------------- ------- ------ ------- -------------------------- 1 PRIMARY <derived2> ALL (NULL) (NULL) (NULL) (NULL) 3438331 (NULL) 2 DERIVED room_break_history index idx_from_user_id idx_from_user_id 21 (NULL) 3438331 Using where; Using index
4.Execution time:
Execution Time: 17.182 sec
Transfer Time: 0.001 sec
Total Time: 17.184 sec
5. Description, judging from the execution plan, type is index, key and key_len are normal. It seems that the index is removed, but the rows are almost the entire table record (not accurate, it is a full table scan), more than 3 million The data execution time is actually 17 seconds.
Thinking: After changing the nullable of the field to not null, key_len becomes shorter. Is the judgment logic of whether it is empty added to the data?
Articles about null:
Improvements:
1.Add index
ALTER TABLE `test`.`room_break_history_tmp_test` -> ADD INDEX `idx_handle_time` (`handle_type`, `create_time`);
2.Execution plan
id select_type table type possible_keys key key_len ref rows Extra ------ ----------- --------------------------- ------ -------------------------------- --------------- ------- ------ ------ -------------------------------------------------------- 1 PRIMARY <derived2> ALL (NULL) (NULL) (NULL) (NULL) 2 (NULL) 2 DERIVED room_break_history_tmp_test range idx_from_user_id,idx_handle_time idx_handle_time 7 (NULL) 1 Using index condition; Using temporary; Using filesort
3. Execution Time : 0.178 sec
Transfer Time : 0 secTotal Time : 0.179 sec
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