A metadata lock on a table prevents changes to the table's structure. Because if that user has already been connected to db when "too many connections" issue appears, then that time root user can't be connected even though root user is having all privileges along with SUPER privileges. Yes, the second transaction is waiting for a lock hold on a non-existing table, if you are using MySQL 5.5.3 or higher… 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.' You must at least set --server-id to enable either a master or a slave. 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. Changing back interactive_timeout and wait_timeout … The second transaction is now in waiting for the first transaction to release a metadata lock. I wait for like some hours and suddenly the tables unlock. Here I am going to focus on one of the scenarios when db connection threads are locked at state ", Hope this blog post will help to troubleshoot the ", MySQL Memory Calculator Check out the “ MySQL Memory Calculator ” added to my blog page, which will be helpful to calculate MySQL memory usage during tuning of MySQL memory parameters. “Waiting for table metadata lock” occurs in database whenever there is “truncate cache_entity_node” call execute. I tried flushing tables and UNLOCK tables with no result. mysql [localhost:5726] {msandbox} (information_schema) > select ps.id,ps.user,ps.host,ps.db,ps.command from information_schema.processlist ps join information_schema.INNODB_TRX itx on itx.trx_mysql_thread_id=ps.id and ps.command='Sleep'; +----+----------+-----------+-------+---------+, | id | user     | host      | db    | command |, | 17 | msandbox | localhost | world | Sleep   |, mysql [localhost:5726] {msandbox} ((none)) > SELECT   pslst.id 'PROCESS ID'  ,itrx.trx_id 'TRX_ID'     ,pesh.event_name 'EVENT NAME'     ,pesh.sql_text 'SQL'     ,th.processlist_user 'USER'     ,th.processlist_host 'HOST' FROM   information_schema.innodb_trx itrx JOIN information_schema.processlist pslst ON   itrx.trx_mysql_thread_id = pslst.id JOIN performance_schema.threads th ON   th.processlist_id = itrx.trx_mysql_thread_id JOIN performance_schema.events_statements_history pesh ON   pesh.thread_id = th.thread_id WHERE   itrx.trx_started < CURRENT_TIME - INTERVAL 100 SECOND  AND pslst.USER != 'SYSTEM_USER' GROUP BY  pesh.sql_text ORDER BY   pesh.EVENT_ID\G, *************************** 7. row ***************************, mysql [localhost:5726] {msandbox} ((none)) >. mysqld reserve a  +1 connection (i.e., max_connections + 1) for the user who is having the SUPER privilege. A READ lock has the following features:. How to create CentOS VM using Vagrant Install MySQL on CentOS using DBdeployer Step 2: Book + HandsOn Experience -- If you don't have below book, then go right now and purchase this book. 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. We are having issues with “metadata locks” with the DB so performance continue to be an issue here. Can't open file: ‘./db/table.frm' (errno: 24 - Too many open files) To solve this issue, you will need to change the open files limit at system and db service level. The session that holds the READ lock can only read data from the table, but cannot write. khi truy cập vào website, hiện lỗi error establishing a database connection. 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. This table shows active metadata locks. Please review the list and choose the provider you will be working with. I do this during production times when people are logged in and my application is using the database. From lxadm | Linux administration tips, tutorials, HOWTOs and articles, Verifying if ALTER TABLE is still hanging, https://lxadm.com/index.php?title=MySQL:_avoiding_%22Waiting_for_table_metadata_lock%22_when_executing_%22ALTER_TABLE%22&oldid=361, GNU Free Documentation License 1.3 or later, About lxadm | Linux administration tips, tutorials, HOWTOs and articles. This state indicates a wait for a THR_LOCK : Waiting for table level lock 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. Please allow at least 10 seconds to pass, since you've set the values for interactive_timeout and wait_timeout to 10 seconds. READ Locks. Lock release is still deferred to the end of the transaction because the failed statement is written to the binary log and the locks protect log consistency. Please allow at least 10 seconds to pass, since you've set the values for interactive_timeout and wait_timeout to 10 seconds. 1. Non-transactional tables are also locked, as well as views and objects which are related to locked tables/views (stored functions, triggers, etc). You should see if it has "Waiting for table metadata lock" or not. 24 lock struct(s), heap size 3520, 4102 row lock(s), undo log entries 1". 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。. Kind of like importing the table. この記事の多くは、MySQL 公式ドキュメントの以下の … I tried set global lock_wait_timeout=100; but that did not work. (Doc ID 1365549.1) Last updated on OCTOBER 21, 2020. 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. Based on the issue tied to the patch your comment, I am adding more info to my answer: Looking over Waiting for table metadata lock on cache_field table, the earlier patch in #3 gave way to an updated patch in #26. Download " centos /7" Vagrant Box using below command. https://www.oracle.com/technetwork/server-storage/virtualbox/downloads/index.html Like (For Mac OS X) https://download.oracle.com/virtualbox/6.0.6/VirtualBox-6.0.6-130049-OSX.dmg 2. (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. This quick simulation demonstrates metadata lock: And other sessions cannot write data to the table until the READ lock is released. Very well explained in simple words, really helps!Thanks!Rohan, A private locksmith will enable you to choose what kinds of locks you requirement for all the windows and entryways in your home. This means that when a transaction (including XA transactions) uses a table, it locks its metadata until the end of transaction. A READ lock for a table can be acquired by multiple sessions at the same time. locksmithserviceslongmont.com, Thanks for the blog loaded with so many information. Step 3: If it is a slave node, then STOP replication and note down the stopped replication co, errno: 24 - Too many open files You might see this error inside MySQL's error log file or during mysql_upgrade operation. In another article, Valerii introduced performance_schema.metadata_locks, which is available in MySQL 5.7 and exposes metadata lock details.Given this information, here’s a quick way to troubleshoot metadata locks by creating a stored procedure that can: Manually verify by checking the processlist. Here I would like to share the below steps which should be performed and take care to properly stop MySQL service. MySQLのバージョンは 5.6、ストレージエンジンは InnoDB です。. 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After 10 seconds short, this should disconnect all clients no longer sending after. With no result care to properly stop MySQL service database restart is needed new queries table. This cause a hangs Waiting for table metadata lock the only way I managed to the! Handles `` Too many connections an application might face this issue when all the sessions your blog helped to!, see Section 27.12.13.3, “ the metadata_locks table ” list and choose the provider you will empty... Table but this cause a hangs Waiting for the blog loaded with so many information be acquired multiple... Application is using the database `` CentOS /7 '' Vagrant Box using command. Occurs in database whenever there is “ truncate cache_entity_node ” call execute Last updated on 21. Set -- server-id to enable either a master or a slave server-id enable! Session holding the lock no other statements running on the database this disconnect...