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  1. MariaDB Server
  2. MDEV-9743

long "query end" stage on a simple update sql

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      Description

      Using the follwing test sql:

      DROP DATABASE IF EXISTS `my_test`;
      CREATE DATABASE `my_test`;
      USE `my_test`;
       
      DROP TABLE IF EXISTS `test`;
      CREATE TABLE `test` (
              `id` TINYINT UNSIGNED NOT NULL AUTO_INCREMENT,
              `size` INT UNSIGNED NOT NULL,
              PRIMARY KEY (`id`)
      )ENGINE=Innodb;
      insert into my_test.test values(0,100);
      

      SET profiling = 1;
      #this update has short query end 
      update my_test.test set size=100 where id=1;
      #this update has long query end 
      update my_test.test set size=size+100 where id=1;
      SHOW PROFILE for query 1;
      SHOW PROFILE for query 2;
      

      I find that update my_test.test set size=size+100 where id=1; has a very log "query end" stage:

          [root@localhost code]# /usr/local/mysql/bin/mysql < test.sql | grep "query end"
      query end	0.000007
      query end	0.005163
      

      I have used the same test.sql on mysql 5.1 ,and no such thing happaned:

      [root@localhost ~]# mysql < test.sql | grep "query end"
      query end	0.000003
      query end	0.000002
      

      Of course,the config files of mariadb 10.1.12 and mysql 5.1.73 are different.But the update sql is so simple that I don't think the difference in config files can cause this huge performance slowdown.But I have upload my mariadb config file.

      =============updated in 2016/03/17=================
      Sorry for my brief description yesterday.Now I rerun the test.sql in my virtualbox centos 7 machine and check the full stages,the result is the same:

      [root@localhost code]#  /usr/local/mysql/bin/mysql < test.sql 
      Status	Duration
      starting	0.000084
      checking permissions	0.000012
      Opening tables	0.000017
      After opening tables	0.000006
      System lock	0.000004
      Table lock	0.000006
      init	0.000131
      updating	0.000059
      end	0.000010
      query end	0.000009
      closing tables	0.000004
      Unlocking tables	0.000008
      freeing items	0.000013
      updating status	0.000011
      cleaning up	0.000004
       
      Status	Duration
      starting	0.000036
      checking permissions	0.000006
      Opening tables	0.000012
      After opening tables	0.000005
      System lock	0.000004
      Table lock	0.000005
      init	0.000037
      updating	0.000073
      end	0.000007
      Waiting for query cache lock	0.000003
      end	0.000009
      query end	0.003902
      closing tables	0.000012
      Unlocking tables	0.000012
      freeing items	0.000010
      updating status	0.000025
      cleaning up	0.000004
      

      Actually,I have tried to batch exec the "update my_test.test set size=100 where id=1;" 10000 times and "update my_test.test set size=size+100 where id=1;" 10000 times,and got the following results:

      [root@localhost code]# time /usr/local/mysql/bin/mysql < stmt1.sql 
       
      real	0m0.667s
      user	0m0.037s
      sys	0m0.102s
      [root@localhost code]# time /usr/local/mysql/bin/mysql < stmt2.sql 
       
      real	0m56.015s
      user	0m0.187s
      sys	0m0.316s
      [root@localhost code]# wc -l stmt1.sql  stmt2.sql 
       10000 stmt1.sql
       10000 stmt2.sql
       20000 total
      

      I found this problem because in our performance testing , I used pt-query-digest to analyze the slow query log and found the exce time of a simply update sql is 88% of the overall exec time:

      # Profile
      # Rank Query ID           Response time   Calls R/Call V/M   Item
      # ==== ================== =============== ===== ====== ===== =============
      #    1 0x919A71601652CD9C 1880.7490 88.8%  1000 1.8807  0.21 UPDATE uisdb.maildir
      #    2 0x6A6BF8323EF9A924   64.4834  3.0%  1000 0.0645  0.03 INSERT UPDATE uisdb.mail_entity
      #    3 0x0CFA48C3B4E6316C   60.1811  2.8%  1000 0.0602  0.02 INSERT uisdb.mail
      #    4 0xB577AD2502F24975   49.4235  2.3%  1103 0.0448  0.02 SELECT uisdb.mail_entity
      # MISC 0xMISC               63.1927  3.0% 44938 0.0014   0.0 <53 ITEMS>
       
      # Query 1: 20.83 QPS, 39.18x concurrency, ID 0x919A71601652CD9C at byte 40584611
      # This item is included in the report because it matches --limit.
      # Scores: V/M = 0.21
      # Time range: 2016-03-17 01:29:20 to 01:30:08
      # Attribute    pct   total     min     max     avg     95%  stddev  median
      # ============ === ======= ======= ======= ======= ======= ======= =======
      # Count          2    1000
      # Exec time     88   1881s    20ms      3s      2s      3s   628ms      2s
      # Lock time     99   1833s    57us      3s      2s      3s   625ms      2s
      # Rows sent      0       0       0       0       0       0       0       0
      # Rows examine   3    1000       1       1       1       1       0       1
      # Rows affecte  13    1000       1       1       1       1       0       1
      # Query size     0  89.84k      92      92      92      92       0      92
      # String:
      # Hosts        localhost
      # Users        uis
      # Query_time distribution
      #   1us
      #  10us
      # 100us
      #   1ms
      #  10ms  ##
      # 100ms  #####
      #    1s  ################################################################
      #  10s+
      # Tables
      #    SHOW TABLE STATUS FROM `uisdb` LIKE 'maildir'\G
      #    SHOW CREATE TABLE `uisdb`.`maildir`\G
      update uisdb.maildir set next_uid=last_insert_id(next_uid)+1 where mb_id=12 and maildir_id=1\G
      # Converted for EXPLAIN
      # EXPLAIN /*!50100 PARTITIONS*/
      select  next_uid=last_insert_id(next_uid)+1 from uisdb.maildir where  mb_id=12 and maildir_id=1\G
      
      

      uisdb.maildir is a simple table with 3000+ rows and the "where condition" uses its primary key to search:

      MariaDB [(none)]> explain select  next_uid=last_insert_id(next_uid)+1 from uisdb.maildir where  mb_id=12 and maildir_id=1\G
      *************************** 1. row ***************************
                 id: 1
        select_type: SIMPLE
              table: maildir
               type: const
      possible_keys: PRIMARY,mb_id
                key: PRIMARY
            key_len: 12
                ref: const,const
               rows: 1
              Extra: 
      1 row in set (0.30 sec)
      

      Our servers are not particularly tuned for mariadb except in the my.cnf files.If you need more env config,please tell me.

      PS:when I googled this problem,someone seemed to encount the same problem,at this link

        Attachments

        1. my.cnf
          2 kB
        2. pt-query-digest.txt
          45 kB
        3. stmt1.sql
          439 kB
        4. stmt2.sql
          488 kB
        5. test.sql
          0.5 kB

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            • Assignee:
              Unassigned
              Reporter:
              cyy chen yuanyuan
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                Updated:
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