Waiting for query cache lock To fix this error, you can try the following solutions: 2) There’s a mutex around the code that handles query cache write, which means only 1 connection writes to the cache at a time. When the duration of the lock wait time is extended, this results in a slow down of SQL 2、即便query_cache_size = 0，但 query_cache_type 非 0 的话，在实际环境中，可能会频繁发生 Waiting for query cache lock； 3、一开始就设置 query_cache_type = 0 的话，没有办法 I loaded up the normal SHOW FULL PROCESSLIST; and saw that there were alot of "Waiting for query cache lock" processes running. Waiting for query cache lock Waiting to take a query cache A wait for a “library cache pin” implies some other session holds that PIN in an incompatible mode. Locks that have been requested but not yet granted (shows which sessions are waiting for which metadata locks). This is quite a problem, because for example, also the adding to The query cache stores results of SELECT queries so that if the identical query is received in future, the results can be quickly returned. Source has sent all binlog to replica; waiting for more updates 이때의 상태는 Waiting for query cache lock 으로 표시된다. An easy way to review/monitor your The lock contention problems would still be an issue, but you would see the limit hit when "SHOW PROCESSLIST" lists an excessive number of "Waiting for query cache lock" proceses. Learn how to detect an issue with mysql query caching, by finding “waiting for query cache lock” appearing 1 I increased our servers query_cache_size to 2gb, hoping for performance benefits. It caches SQL statements and the corresponding result sets. This is implemented as a table lock, outside the storage 文章浏览阅读1k次。文章描述了MySQL客户端在加锁后出现宕机问题，导致业务中断。通过查看错误日志和分析`show processlist`输出，发现大量`Waiting for query cache lock`状态，推测查 For appeals, questions and feedback about Oracle Forums, please email oracle-forums-moderators_us@oracle. This may even happen during a bug fix patch release. com. in/emfhKYmU 𝐹𝑜𝑙𝑙𝑜𝑤 Oracle Database -- Resolving "library cache pin" wait event Problem Altering a procedure is taking too long. Application 2、即便query_cache_size = 0，但 query_cache_type 非 0 的话，在实际环境中，可能会频繁发生 Waiting for query cache lock； 3、一开始就设置 query_cache_type = 0 的话，没有办法 The library cache lock controls the concurrency between clients of the library cache by acquiring a lock on the object handle so that either: One 文章浏览阅读513次。本文详细解析了MySQL Query Cache的工作原理、优化参数及其在不同场景下的适用情况，包括如何合理设置query_cache_size、query_cache_type等参数以避免性能 Query GDB shows that 'row cache lock' (from request till release) is completely held within 'library cache lock' holding. Optimize your database performance—read the full guide now! MySQL thread status: Waiting for query cache lock. The bigger the QC, the Waiting for query cache lock This state occurs while a session is waiting to take the query cache lock. in/eGzyXUUb 𝐹𝑜𝑙𝑙𝑜𝑤 Lock timeout detection is a database manager feature that prevents applications from waiting indefinitely for a lock to be released. timeout property. For this problem, I have tried various things that I Then the Query Cache Lock lock mechanism will cause very frequent locked conflicts, and wait for the Query Cache Lock unlocked to this table, causing the Query Cache Lock to unlock, resulting in Oracle Cloud Infrastructure - Database Service - Version N/A and later: Library Cache Lock and Library Cache Pin wait on Sessions While Executing PL/SQL Package in P Hello everybody Today on my environment I killed a session while compiling a procedure that was taking too much time. Hi , i want to know about wait events of library cache pin and library cache lock in my environment i have faced this issue but i am not able to get session whos is waiting for library cache . The following discussion provides some information on how Many of these wait events are tied to the internal implementation of Oracle and therefore are subject to change or deletion without notice. So a query insert/send operations typically How we resolved a performance degradation caused by pileup of queries stuck in "Waiting for query cache lock" state in #MySQL and #MariaDB. 4 and later: 'library cache lock' Waits: Causes and Solutions query_cache_type = OFF slow_query_log = 1 # log slow queries, for debuging long_query_time = 1 # log queries as slow when their duration > 1 sec innodb_buffer_pool_size = A lock wait occurs when a transaction tries to obtain a lock on a resource that is already held by another transaction. This feature was intended as a way to improve The error “waiting for cache lock ubuntu var/lib/dpkg/lock-frontend” occurs due to the involvement of the dpkg package manager in another running process. (Or if the blocker does have a lock wait, we want to know who is at the root of But, No cache directive query still wait for query cache lock on query_cache_type=2 (DEMAND) mode server. 文章浏览阅读533次。本文针对线上detail页面加载缓慢的问题进行定位，发现SQL查询虽然使用了主键，但在MySQL的查询缓存中出现了写竞争，导致大量线程阻塞。通过调 Oracle Database Cloud Schema Service - Version N/A and later: Resolving Issues of "Library Cache Pin" or "Cursor Pin S wait on X" This wait event happens when a session tries to access a block in the buffer cache but it can't because the buffer is busy, that is another session is modifying the block and the contents of When you see a thread in the Waiting for table flush state, that should mean that the FLUSH TABLES [WITH READ LOCK] statement was issued and was still running when the query The length of time in milliseconds the persistence provider should wait to obtain a lock on the database tables may be specified using the javax. This message typically appears when you try to run package management Library cache lock We can explore library cache locks when gather statistics reaches the breakpoint on qostobkglrel and split partition is waiting on the library cache lock: set pagesize 20 In the world of database management, MySQL Query Cache has played a crucial role for years. The library cache is a memory area within Actions in this state include flushing the binary log or InnoDB log, and some cleanup of the query cache. A library cache pin will be obtained on a database object that is currently cached In some situations it may happen that your session is hanging and is waiting for a 'Library cache lock'. I am facing performance issue in my application. In the first run, that report only took 19 minutes, and it took over 2 hours in the other runs, including the last. This was fairly consistent as I refreshed the list But, No cache directive query still wait for query cache lock on query_cache_type=2 (DEMAND) mode server. When working with Ubuntu, you might have encountered the frustrating message Waiting for cache lock. event, 1, 40) event, The AWR shows as ‘Waiting for event "library cache lock" in wait class "Concurrency"’. 20, and removed in MySQL 8. 5 or newer stephane gault's insight: 文章浏览阅读524次。本文分析了MySQL查询缓存导致的系统性能问题，并详细解释了查询缓存的工作原理及存在的问题，最后给出了关闭查询缓存的解决方案。 Enable the slow query log to troubleshoot bad queries Increasing the query_cache size over 128M may reduce performance Adjust your join queries to always utilize indexes Increase table_cache But LOCK TABLES acquires a different type of lock. They don't But, No cache directive query still wait for query cache lock on query_cache_type=2 (DEMAND) mode server. Now usually if a single query is causing many others to lock then it should There is now a 50ms timeout for a SELECT statement waiting for the query cache lock. I checked processlist and I get 'Waiting for The “library cache pin” wait event in an Oracle database occurs when a session is waiting to acquire a shared lock on an object in the library cache. 7. Cursor: Pin S Wait On X and library cache lock Sometimes your MySQL query cache is a deprecated feature due to various issues, therefore it is best to disable it. lock. How we resolved a performance degradation caused by pileup of queries stuck in "Waiting for query cache lock" state in MySQL and MariaDB. entries in the query_cache for the given table are purged when write occurs to that table. 7, such as checking, invalidating, storing, and sending query results. The error waiting for cache lock: could not get lock /var/lib/dpkg/lock-frontend is caused by a file lock conflict. In addition, any insert, update, delete or other modifications to a table causes any relevant entries in the query Note: Although query cache is deprecated as of MySQL 5. So, I started focusing on MySQL configuration variables Tags: I am running a simple query on a simple table on the same machine as the server running 5. 4GHz、3GB RAM的服务器上运行一个从2000万行表中检索7000行数据的简单查 But, No cache directive query still wait for query cache lock on query_cache_type=2 (DEMAND) mode server. I see a system lock for 2 State: storing result in query cache 2 State: Sending data 1 State: Waiting for master to send event 关闭query cache 后： 1067 State: 1 State: Waiting for master to send event 1 State: 11210:20081211:102722 Query failed:Lock wait timeout exceeded; try restarting transaction [1205] Tags: None How to resolve library cache lock in oracle First, we can identify all the sessions which are waiting on the Library cache lock using the below sql This state occurs while a session is waiting to take the query cache lock. If the timeout expires, the statement executes without using the query cache. It's a metadata lock, which uses a different timeout option, lock_wait_timeout. SQL Server Performance Tuning Using Wait Statistics SQL Server performance tuning is a critical part of maintaining the health and efficiency of a It looks like some sort of dead lock, but I cannot understand why. This can occur when InnoDB waits for a table-level lock during execution of LOCK TABLES. This meant that transaction was not really It seems Query_cache_table should introduce a rw-lock which should be acquired in read mode on query processing and in write mode on table invalidation. In the last one, when that final report started, the query cache had about 160k low Resolving "Waiting for Cache Lock" Issue on Ubuntu Systems: A Guide Ubuntu and other Debian-based Linux distributions are renowned for their stability, ease of use, and extensive software The Server Query Cache (QC) is a well-known feature of MariaDB Server. They don't I also have examples where there are multiple (killed) Waiting for query cache lock threads and a single DROP closing tables The mariadbd consumes 100% CPU but I'm not sure what A result found in the query cache is being sent to the client. If there are errors due to lock time-out or performance issues due to lock waits, the recommendation is to review the transactions Query profiling shows "Waiting for query cache lock" but query_cache_size is 0 We have a statement based replication server that has been experiencing slowdowns and during the event SHOW FULL So the unstable response times did not come from a bad execution plan, but rather from contention/excessive waiting somewhere in the server. Upon profiling most of the time is Learn what MySQL query cache is and some basic understanding for how it works. While Aurora MySQL doesn't allow usage of MyISAM tables to store persistent data, they are used to store internal 标签：Mysql InnoDB Waiting 线上数据库中，如果是InnoDB的话，配备足够的innodb buffer pool后，就把query cache关闭掉（query_cache_size 和 query_cache_type 同时设置为 0），大量的更新+查询 In this article, Jaime will show you a quick way of troubleshooting metadata locks by using performance_schema and a stored procedure in Prior to MySQL 5. They don't When concurrent sessions try to update optimizer statistics for the same object, all of them except the one that successfully acquired all necessary locks/pins on the library/row cache entries, wait on this Find the 'lock' folder within your moodledata directory and manually remove all the contents via FTP. 9 We have a statement based replication server that has been experiencing slowdowns and during the event SHOW FULL PROCESSLIST showed the replication query stuck on "Waiting for query cache Learn about the thread states associated with the query cache in MySQL 5. In the source code, server only checks if there's SQL_NO_CACHE directive. 5. This table shows all queries in the query cache. 1. This can happen for any statement that needs to perform some query cache operation, such as an A result found in the query cache is being sent to the client. I will explain how to solve Concurrency Wait Event ( library cache lock and Cursor: Pin S Wait On X ) in Oracle in this article. This can happen for any statement that needs to perform some query cache operation, such as an Waiting for table level lock But what I also noticed, what that ALL of these queries with "table level lock", was only queries which had something to do with my table called users. (hence both locks can be held at the same time, and 'library cache 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. Enq: TX – Row lock contention This type of event is application level locking problem that occurs Proxy_cache_lock logic means that when NGINX receives couple of request simultaneously, it sends only one upstream and the rest waiting till the first one returns and insert to 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. How we resolved a performance degradation caused by pileup of queries stuck in "Waiting for query cache lock" state in #MySQL and #MariaDB. The respective SQL statement is one of the frequently When concurrent sessions try to update optimizer statistics for the same object, all of them except the one that successfully acquired all necessary locks/pins on the library/row cache entries, wait on this To avoid these kinds of situations, the user locks (READ lock or WRITE lock) the table, which puts other users on wait. It is taking 22sec to return ~7000 rows from a 20 million row table. to 5. https://lnkd. " 「Waiting for query cache lock」は、文字通りセッションのクエリキャッシュロック取得待ちイベントを示します。 つまり Aurora ではSQLス Thanks for posting, part of our hosting move or new client host tuning is that we first tune the mysql engine. For example, the MyISAM storage engine uses file @Advait for anyone reaching here, your best bet would be to either wait for the process to finish or kit it. This should resolve the error, or at the very least allow you to regain access to the Moodle site to 服务器上，发现sql状态Waiting for query cache lock，如下图： query cache 的lock是一个全局的锁，所以当你的写入并发和读取并发都很大的时候，这个锁是一个主要竞争点。 特别是当 But, No cache directive query still wait for query cache lock on query_cache_type=2 (DEMAND) mode server. The users on the waiting After getting in touch with AWS support and long investigations we discovered that the max_tmp_table was set to 32 and since we had a large number of concurrent requests on a view Waiting for a load lock indicates that there is a blocker with a higher or incompatible mode. Waiting for query cache lock is a state that occurs If the query_cache_type system variable is set to 1, or ON, all queries fitting the size constraints will be stored in the cache unless they contain a SQL_NO_CACHE Learn what MySQL query cache is and some basic understanding for how it works. 3 a statement that opened a table only held meta data locks till the end of the statement and not the end of the transaction. Metadata locking is not a replacement for the table definition cache, and its mutexes and locks differ from the LOCK_open mutex. persistence. Learn how to detect an issue with mysql query caching, by finding “waiting for query cache lock” appearing Then the Query Cache Lock lock mechanism will cause very frequent locked conflicts, and wait for the Query Cache Lock unlocked to this table, causing the Query Cache Lock to unlock, resulting in Waiting for query cache lock This state occurs while a session is waiting to take the query cache lock. Termux: pkg update shows "Waiting for cache lock" and it doesn't seem to stop Asked 3 years, 2 months ago Modified 1 year, 8 months ago System lock Requesting or waiting for an external lock for a specific table. Learn На практике сталкивались с тем, что при query_cache_size более 512M все чаще появляются процессы, кратковременно подвисающие в состоянии «waiting for query cache Oracle Database Exadata Express Cloud Service - Version N/A and later Oracle Database Backup Service - Version N/A and later Information in this document applies to any The QUERY_CACHE_INFO plugin creates the QUERY_CACHE_INFO table in the INFORMATION_SCHEMA database. Lock requests that have been The keycache->cache_lock mutex controls access to the key cache for MyISAM tables. Checking the wait events for the session shows that the session is waiting on the storing result in query cache 服务器将查询结果存储在查询缓存中。 Waiting for query cache lock 当会话等待获取查询缓存锁时会出现此状态。 这可能发生在任何需要执行某些查询缓存操作的语句中，例 Oracle Database Cloud Schema Service - Version N/A and later: How to Mark Hot for the query which are contending with Library Cache Lock and Cursor pin waits. I have 20 How we resolved the performance degradation caused by pileup of queries stuck in “Waiting for table flush” state in MySQL. The storage engine determines what kind of external lock to use. They don't The query holding the lock who is blocking does not have the wait. Querying this WRITE locks normally have higher priority than READ locks to ensure that updates are processed as soon as possible. Try running the query without query cache. Upon profiling most of the time is But cacheable queries take out an “exclusive lock” on MySQL’s query cache. They don't 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. This means that if one session obtains a READ lock and then another session I will explain Enq: TX – Row lock contention Wait Event in Oracle Database in this post. 1 community version of MySQL in Windows 2008 server. After changing all tables to InnoDB, run MySQLTuner again and adjust InnoDB buffer pool mysql query cache 今天发现一个坑，数据库负载突然升高，并出现大量的waiting for query cache lock，进程锁死。线上配置为query_cache_size =50M，query_cache_type 的值为 2。通 The Row Cache or Data Dictionary Cache is a memory area in the shared pool that holds data dictionary information to reduce physical I/O on the Explore the causes and solutions for Oracle row cache lock wait events. In the end some queries time out, I receive notifications about lock wait timeout For production systems with lots of writes, you may as well turn OFF the query_cache. This information enables you to understand metadata lock dependencies between sessions. 2) Also note that Waiting for query cache lock means that some other thread acquired the cache lock, and prevents this query to write to cache. Simultaneous SELECT and INSERT in one database seems to cause a dead lock with query cache update by INSERT ON DUPLICATE Library cache resource types waited for over the life of the instance set linesize 152 column average_wait format 9999990. They don't 博客内容涉及MySQL查询性能问题，特别是关于'等待查询缓存锁定'的状态消耗了大量时间。作者在一台2. You can see not only which lock a session is waiting for, but which session currently holds that lock. 1) Last updated on SEPTEMBER 17, 2025 Applies to: Oracle Database - Enterprise Edition Learn how to use SQL Server Wait Statistics to help diagnose performance problems. The following query will list waiters and the holder of the resource along with the The extension keeps spinning around, causing a Blocking waiting for file lock on package cache. 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. Waiting for query cache lockis a connection status specific toMySQL 5. 5 and currently the load on server is 150 When I do show process list I see a lot of queries with status Waiting for query cache lock And But, No cache directive query still wait for query cache lock on query_cache_type=2 (DEMAND) mode server. I end up with a state where every query is stuck in a waiting state. Locks map to Instance Locks. To kill it, first find it: ps -ef | grep apt Then I checked my MySQL process log, and I noticed a huge list of queries with: Waiting for table level lock But what I also noticed, what that ALL of these queries with "table level lock", was I have configured mariadb with following config: query_cache_size = 0 query_cache_type = 0 But still mariadb hangs after a while with CPU 100%. we found that a sample query for update object, acquired intent lock 17000 times and had to yield those many times. After sometime the query performance would drastically decrease. Once I dug in deeper, I found the @dezlov the dead lock "Waiting for query cache lock" is usually coming from write contention on the query cache, because it's too big and mysql spend more time to invalidate that 记录MySQL因Waiting for query cache lock导致业务宕机的处理，早上10点，业务反馈服务器502无法访问，查询所有的WEB服务器、缓存、数据库都是可以连接的。 但是MySQL查询一致卡 I am using MySQl 5. Additionally, when Currently our DB locks very often when a process runs, so all other processes are waiting until the current process finishes. A good candidate for contention issues was Resolving Issues Where 'enq: TX - row lock contention' Waits are Occurring (Doc ID 1476298. Since a collection scan is a long-running query it will yield multiple times A lock wait occurs when a transaction tries to obtain a lock on a resource that is already held by another transaction. The How about adding a serial column on the cache and then doing SELECT serialid FROM cache ORDER BY serialid DESC LIMIT 1; DELETE FROM cache WHERE serialid < {selected_id}? For example, the thread is going to request or is waiting for an internal or external system lock for the table. 2、即便query_cache_size = 0，但 query_cache_type 非 0 的话，在实际环境中，可能会频繁发生 Waiting for query cache lock； 3、一开始就设置 Around 10 hours ago we upgraded our server from 5. storing result in query cache Saving the result of a query into the query cache. Query Cache는 싱글 코어에서 동작하도록 설계 되어, 현재의 멀티 코어 시스템에서 Oracle Database - Personal Edition - Version 8. 00 select substr (e. 0. Technical questions should be asked in the appropriate category. This document describes how to find the session that is holding the lock that you are In viewing the process list, it seems that the degradation corresponds to frequent TRUNCATE TABLE statements which run on the test db (to reset the db state for the next test). Now, after more than a couple of hours that session is still there MySQL Threads waiting for Query Cache lock? What causes the waits on the Query cache? #mysqldba #mysql #performance #opensource I've a simple query that is taking way to much time to process, the query is very simple and the WHERE clause has just simple comparators but the query takes between 15 to 20 secs to Locks are held in the database to ensure data consistency. 0, it is still a powerful tool if you’re using supported How can I calculate the total time my MySQL database is spending Waiting for query cache lock ? I've found two specific very simple tables that adding a 2) Also note that Waiting for query cache lock means that some other thread acquired the cache lock, and prevents this query to write to cache. Waiting for query cache lock Waiting to take a query cache Tags: I am running a simple query on a simple table on the same machine as the server running 5. This can happen for any statement that needs to perform some query cache operation, such as an INSERT or DELETE that This will show you a list of all current processes, their SQL query and state. When the duration of the lock wait time is extended, this results in a slow down of SQL Waiting for cache lock, Programmer All, we have been working hard to make a technical sharing website that all programmers love. yyzq ncw tgbapg dzgof mem hhkdx nhlk yetlk tcps sjqnvo mejw eihae jsjx oihmi knggfc