If the server acquires metadata locks for a statement that is syntactically valid but fails during execution, it does not release the locks early. (Here Please, you don't judge that below-suggested book is for 5.0 version whereas you are going to prepare for MySQL 5.6/5.7 DBA certification exam. 1. When this issue appears, Only the user with the SUPER privileges can be connected if any other user who has SUPER privileges is not already connected to the database and we have reached max_connections. 006725 Read_Master_Log_Pos: 4508785 Relay_Log_File: db -test-relay-bin . A) Using InnoDB Engine Status All other threads are present in the SLEEP state. It failed because the table did not exist. PROBLEM : db -test (none ) > show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: xxxxx Master_User: rep_user Master_Port: 3306 Connect_Retry: 60 Master_Log_File: db -test-02-bin . Even if you don't see any processes using your particular table (in SHOW PROCESSLIST / SHOW FULL PROCESSLIST) - MySQL may still not ALTER your table and do "Waiting for table metadata lock" - because there are some connections made to the database which didn't disconnect yet. 006725 Slave_IO_Running: Yes Slave_SQL_Running: No Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Igno, Master has purged binary logs containing GTIDs that the slave requires Problem : Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'The slave is connecting using CHANGE MASTER TO MASTER_AUTO_POSITION = 1, but the master has purged binary logs containing GTIDs that the slave requires.' The server is waiting to acquire a THR_LOCK lock or a lock from the metadata locking subsystem, where lock_type indicates the type of lock. the only solution is to kill this stmt. gigabytes or more). If you're running a busy database, the chances are that a ALTER TABLE statement executed will not really work, you will end up with MySQL processlist full of "Waiting for table metadata lock" - including your original ALTER TABLE statement, MySQL processlimit will be reached, and your website/system will no longer work. Waiting for table metadata lock. MySQLで「Waiting for table metadata lock」のエラーが発生して、詳しく知りたくなったので、関連しているオンラインDDLとともに調べ、手元で試してみたことをまとめました。. A metadata lock on a table prevents changes to the table's structure. locksmithserviceslongmont.com, Thanks for the blog loaded with so many information. We are having issues with “metadata locks” with the DB so performance continue to be an issue here. The Performance Schema metadata_locks table exposes metadata lock information, which can be useful for seeing which sessions hold locks, are blocked waiting for locks, and so forth. show processlist; Step 2: If it is the master node, then ensure to stop application write hits on the database by doing either stop an app and put in maintenance OR if we have any failover solution then move write hits on another node. I wait for like some hours and suddenly the tables unlock. I had the exact same problem. Above we can see our thread id 10 is locked at state "waiting for table metadata lock" but on processlist, we can't see any other active thread which is running for table city. 24 lock struct(s), heap size 3520, 4102 row lock(s), undo log entries 1". Here I am presenting 3 cases which will help us, how MySQL handles "too many connections" and reserve 1 connection. When your ALTER TABLE query is finished, remember to set interactive_timeout and wait_timeout values to what they previously were. Applies to: MySQL Server - Version 5.5 and later Information in this document applies to any platform. https://www.abhinavbit.com/p/mysql-memory-calculator.html Photo by Kelly Sikkema on Unsplash, How to properly shutdown MySQL before any maintenance activity We might have different scenarios once we need to stop MySQL service before performing either server or database activity like patching/upgrade. A Blog for MySQL Database Administrators. So, to solve this issue, Run mysql_upgrade command to update/upgrade system tables and then restart M, GTID Replication (Skip Transaction using empty transaction) To skip SQL thread's error in GTID replication setup, Insert empty transaction. 260199 [db_username] localhost [db_name] Query 5609 Waiting for table metadata lock ALTER TABLE cerber_log CHANGE stamp stamp DECIMAL(14,4) NOT NULL 0.000 259971 [db_username] localhost [db_name] Query 6196 Waiting for table metadata lock SELECT count(ip) FROM cerber_log WHERE ip = “184.108.40.206” AND activity IN (7) AND stamp > 15349350 0.000 A metadata lock on a table prevents changes to the table's structure. To increase the likelihood of executing your ALTER TABLE statement without MySQL restart or doing a schedule maintenance, you should substantially lower the values for interactive_timeout and wait_timeout. To check and release the lock you need to kill the session holding the lock. Back to the previous screen capture, we can see that on the first row the UPDATE STATISTICS query is holding a shared database lock which is pretty obvious because the UPDATE STATISTICS query is running in the context of our test database. A.P.E. Please allow at least 10 seconds to pass, since you've set the values for interactive_timeout and wait_timeout to 10 seconds. Waiting for table metadata lock. Manually verify by checking the processlist. Using Rails 3-2-stable when I execute a rake db:drop MySQL (and the rake task) hangs indefinitely with the message 'Waiting for table metadata lock" on … 最近遇到一个问题，老大在线上修改表结构的时候不成功，show processlist 发现大量的 Waiting for table metadata lock 线上大部分业务被阻塞，于是赶紧 kill 掉修改表结构的语句，调查原因。 在这之前我们需要 … Wait for a table prevents changes to the table metadata are having with... Status `` Waiting for table level lock the application and all the sessions be found in MySQL! 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