Detecting locked tables locked by LOCK TABLE

Question

Is there a way to detect locked tables in MySQL  I mean tables locked by the LOCK TABLE table WRITE READ command    Note that readers interested in detecting named locks acquired with GET LOCK should read Show all current locks from get lock instead

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You can use SHOW OPEN TABLES to show each table s lock status  More details on the command s doc page are here

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You can create your own lock with GET LOCK lockName timeOut   If you do a GET LOCK lockName  0  with a 0 time out before you lock the tables and then follow that with a RELEASE LOCK lockName  then all other threads performing a GET LOCK   will get a value of 0 which will tell them that the lock is being held by another thread   However this won t work if you don t have all threads calling GET LOCK   before locking tables  The documentation for locking tables is here  Hope that helps

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This article describes how to get information about locked MySQL resources  mysqladmin debug might also be of some use

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The simplest way is    SHOW OPEN TABLES WHERE In use  gt  0   You get the locked tables only of the current database

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Use SHOW OPEN TABLES  http   dev mysql com doc refman 5 1 en show-open-tables html  You can do something like this  SHOW OPEN TABLES WHERE  Table  LIKE    TABLE NAME    AND  Database  LIKE   DBNAME   AND In use  gt  0    to check any locked tables in a database

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The following answer was written by Eric Leschinki in 2014 15 at https   stackoverflow com a 26743484 1709587  now deleted       Mini walkthrough on how to detect locked tables       This may prevent the database from enforcing atomicity in the affected tables and rows   The locks were designed to make sure things stay consistent and this procedure will prevent that process from taking place as designed       Create your table  insert some rows  create table penguins spam int  ham int   insert into penguins spam  ham  values  3  4         show open tables   show open tables like  penguins        prints   your database penguins    0   0       Penguins isn t locked  lets lock it   LOCK TABLES penguins READ        Check if it s locked   show open tables like  penguins        Prints   your database  penguins 1  0       Aha   It is locked   Lets unlock it   unlock tables       Now it is unlocked   show open tables like  penguins        Prints   your database penguins    0   0       show all current locks  show open tables where in use  lt  gt  0       It would be much more helpful if the MySQL developers put this information in a regular table  so I can do a select my items from my table where my clauses   rather than this stripped down  show table  syntax from system variables

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You could also get all relevant details from performance schema   SELECT OBJECT SCHEMA  OBJECT NAME  GROUP CONCAT DISTINCT EXTERNAL LOCK  FROM performance schema table handles  WHERE EXTERNAL LOCK IS NOT NULL  GROUP BY OBJECT SCHEMA  OBJECT NAME   This works similar as   show open tables WHERE In use  gt  0

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SHOW OPEN TABLES to show each table status and its lock   For named locks look Show all current locks from get lock

[mysql] Detecting locked tables (locked by LOCK TABLE)

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