November 27, 2014

Mass killing of MySQL Connections

Every so often I run into situation when I need to kill a lot of connections on MySQL server – for example hundreds of instances of some bad query is running making server unusable. Many people have special scripts which can take the user, source host or query as a parameter and perform the action. There is also a way to do it just using MySQL with a few commands:

In general this is very powerful approach which I use in a lot of cases to create set of SQL statements by SQL query and when execute it.

It would be nice and clean if MySQL would have some way to “eval” – execute the result set of the query as SQL commands. This would avoid requirement to use temporary file etc.

About Peter Zaitsev

Peter managed the High Performance Group within MySQL until 2006, when he founded Percona. Peter has a Master's Degree in Computer Science and is an expert in database kernels, computer hardware, and application scaling.

Comments

  1. Ahmad Ali says:

    I am facing the problem
    Warning: mysql_connect() [function.mysql-connect]: Too many connections in /home/road2l/public_html/connect.php on line 15
    Error connecting to mysqlToo many connections
    Please help me out.

  2. You are not the only one. I’ve thought that this would be handy several times.

    Create a session variable and then make it so that it can be parsed by the parser?

    Not terribly hard.

    -Brian

  3. peter says:

    Brian,

    Yes that is one possibility. Though I think it is nicer if result set can be executed line by line – the GROUP_CONCAT trick works but it is typically restricted in size.

  4. Sergey says:

    Could you please update your post to point out that this feature is 5.1+?

  5. Robert Wultsch says:

    I prefer the following as it will kill them in a multi threaded manner… (sometimes killing a single query can take a while)

    for i in $(mysql -uroot -pPASS -e ‘show processlist’ | grep ‘search_term’ | awk ‘{print $1}’); do
    mysql -uroot -pPASS -e “kill $i” &
    done

  6. Robert Wultsch says:

    Peter,
    Couldn’t you use prepared statements as an eval?

  7. Nils says:

    could also be a modifier to the client instead of a special sql construct (much like \G)

  8. peter says:

    Sergey,

    PROCESSLIST table exists in MySQL 5.1 as well as Percona patches MySQL 5.0 I actually used later for this test.

  9. Hi Peter,

    With INFORMATION_SCHEMA.PROCESSLIST one can create a stored procedure using server cursor to achieve this. The following procedure accepts a user name and kills all queries for that user.
    server cursors are a MySQL solution for ‘eval’.

    Shlomi

    DELIMITER $$

    DROP PROCEDURE IF EXISTS test.kill_user_queries$$
    CREATE PROCEDURE test.kill_user_queries (kill_user_name VARCHAR(16) CHARSET utf8)
    SQL SECURITY INVOKER
    BEGIN
    DECLARE query_id INT;
    DECLARE iteration_complete INT DEFAULT 0;
    DECLARE select_cursor CURSOR FOR SELECT id FROM INFORMATION_SCHEMA.PROCESSLIST WHERE user=kill_user_name;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET iteration_complete=1;

    OPEN select_cursor;
    cursor_loop: LOOP
    FETCH select_cursor INTO query_id;
    IF iteration_complete THEN
    LEAVE cursor_loop;
    END IF;
    KILL QUERY query_id;
    END LOOP;
    CLOSE select_cursor;

    END$$

    DELIMITER ;

  10. peter says:

    Robert,

    I think you can use prepared statements and user variables to execute 1 statement. I’d like to execute many statements and it is best if they are returned as multiple rows in result set.

  11. peter says:

    Shlomi,

    Thanks. Indeed I’d like some good set of useful Stored Procedures to be available for MySQL so we could just add them to any MySQL installation same as we do with Maatkit – there are many things which are relatively easy with stored procedures but you do not want to write it every time from scratch :)

  12. Peter,

    I agree. I think there are some general-purpose stored procedures kits around. There are also many useful queries+views by Roland Bouman that I know of.
    Would be nice to gather them all into a “utilities” schema.

    PS a prepared statement will not allow “KILL” or “OPTIMIZE” or “ANALYZE” queries. Just the normal SELECT/INSERT/UPDATE/…

  13. peter says:

    Shlomi,

    Yes… This is a design bug which is waiting to be fixed for years.

  14. Chip Turner says:

    Check out mypgrep.py from the google mysql tools project on code.google.com. It basically is a supercharged process grep for mysql, including the ability to kill processes.

  15. A few years ago I wrote an article about how to use Vim with mysql to generate and execute SQL statements. It’s here: http://peterstuifzand.nl/external-programs-in-vim.html

  16. peter says:

    Thanks Chip,

    The good thing with having it done on SQL level is you do not need to install everything – not every server running MySQL has working perl python on php installed

  17. Bryan says:

    If information_schema.processlist doesn’t exist on your version of MySQL, this works in a linux script:

    #!/bin/bash
    for each in mysqladmin -u root -prootpwd processlist | awk '{print $2, $4, $8}' | grep $dbname | grep $dbuser | awk '{print $1}';
    do mysqladmin -u root -prootpwd kill $each;
    done

  18. peter says:

    Bryan,

    Which version of Percona patches are you running ? It exists in recent ones for sure.

    Thanks for command line version though.

  19. Bryan says:

    No Percona patches yet, unfortunately. We’re running the standard MySQL 5.0.77 on Centos.

  20. peter says:

    I see,

    Standard MySQL is not what we call “our” MySQL :)

  21. Glynn Durham says:

    How about a technique like this:

    . File optimizeworld.sfs:

    # Optimize tables in the World database.
    SELECT ‘OPTIMIZE TABLE ‘, CONCAT(TABLE_SCHEMA, ‘.’, TABLE_NAME, ‘;’)
    FROM INFORMATION_SCHEMA.TABLES
    WHERE TABLE_SCHEMA = ‘World';

    . To execute:

    shell> mysql –skip-column-names < optimizeworld.sfs | mysql

  22. Andrew Watson says:

    I do this:

    mysqladmin proc | grep Sleep | sort -r -n -k6 | awk {‘print $1; ‘} | xargs mysqladmin kill

    or something to that effect…

  23. I am wondering if there isn’t a symptom that is missing? I am running a high volume ecommerce site and we switched to Magento from custom app written in vb.net (.net 1.1). Shouldn’t MySql handle all of this? What I am wondering is why my old windows box running doesn’t crash with the same load as my high powered linux box?

  24. haberler says:

    I used the command and the query being run in mysql processlist still running for 28226 and l cant kill it with everything l did. what might else l should try ?
    thanks.

  25. Kirill says:

    Thank you Peter for Percona and for this post!

  26. Thanks Peter. Query is really very helpful to me.

  27. Jitender says:

    Hi, i am using mysql 5.0 which does not have processlist table in information_schema, now is there any way i can list all query which is taking more then x time. Any script will be really appriciated.

  28. sheyda says:

    This may not directly related to this chain, but I landed here to kill massive connection due to the hung drop trigger – I have a dilemma with dropping a trigger on a percona 5.5.27 on a very large table ~ 68 Gig. I get the metadata lock and it hangs.

    I have tried everything. Is it safe to remove the trigger from DB.TRG file? Thanks a lot

  29. Alon says:

    ERROR 1146 (42S02): Table ‘infromation_schema.processlist’ doesn’t exist

  30. @Alon,
    You have a typo. Should be information_schema.processlist

  31. Aptitude says:

    Thank you.. very informative as all your articles.. keep it up.

  32. Aptitude says:

    Very informative as all your articles.. keep it up.

  33. scriptime says:

    i am also wiring about mysql administration on my blog

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