Row cache mutex 19c. 1) Last updated on JULY 20, 2024.

Row cache mutex 19c 3. Why do I See "KQR Row Cache" Notices in the Database Alert Log? (Doc ID 2848849. 5. The result cache has the basic functionality we desire: ability of the DB to intercept queries, compare binds, return a pre-queried result. . 0 to 19. 34 Concurrency BUG - High "row Cache Mutex" Waits - Oracle 19c. Processes will show "waiting for 'row cache lock’” • mode=0 shows the lock is not currently held • request=3 shows we are requesting the latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log In this session, we will compose a new gdb script: "gdb_script_mutex_19c_body_lock_all" (see Appendix 7. SQL> MUTEX_TYPE indicates the action or object the mutex protects, and in the above example there are mutexes protecting library cache objects and acting as cursor pins. fix in 19. 26 Concurrency library cache: mutex X 4,780,489 21,881 5 24. 6. USAGE. Don't Too many row cache objects are being copied or ‘cloned’. SC. Select a discussion category from the picklist. Symptoms. Total number of entries in the cache. 1 and later Oracle Database Cloud Schema Service - Version N/A and later Oracle Database Exadata Cloud Machine - Version N/A and later For example, if 60 seconds of "library cache: mutex X" at the top, and that is from a 61 second sample, than you have a big issue. 10gR2 new library cache latch mechanism that replace latches and takes less memory From Tanel Pode, On 32bit linux installation a mutex was 28 bytes in size, regular latch structure was 110 bytes. Applies to: Oracle Database - Standard Edition - Version 10. Goal. 92 library cache: mutex X Library cache mutexes protect hash buckets within the shared pool. 5K 92. There is no workaround for this problem. For example, in the following Java snippet, a SQL statement object is created, executed, and discarded: library cache: mutex X 321,764 601. Could you please share bug information which you are pointing above. 0 . sql - missing - on if sqlcode statement: 30336530: 32218454: alter database datafile force decrypt should work with files with no key: high wait on row cache mutex when execute query with dblink concurrently: 30713133: 32218454: pdb close operation failure on 19c pod. 2; The High Contention on 'row cache objects' could be on Dictionary Cache for objects "dc_users" or "dc_tablespaces" Systemstate or Hanganalyze dumps show that the waiting process Call Stack Waits for the Waiting Process on "row cache lock" event: That said, there are a couple of bugs relating to dbms_stats & library cache locks. This fix ensures that only the ‘hot’ objects are cloned, not every object on the hash chain. High concurrency waits on 'row cache lock' and 'cursor: pin S wait on X' while the blocker is waiting for 'Disk file operations I/O' on a password file. 4 and later Oracle Database - Enterprise Edition - Version 8. Each query used in the database is parsed by Oracle for correctness and then stored an area of the shared pool as a cursor. The E-Business Suite 19c Database Upgrade Analyzer is a self-service health-check script that reviews E-Business R12 19c Database Upgrade related data, analyzes current configurations and settings for the environment and provides feedback and recommendations on the progress of your 19c database upgrade and any potential missing or failed upgrade steps. Rows with the following NAMESPACE values reflect library cache activity for SQL statements and PL/SQL blocks: SQL AREA. Distributed recovery process. 2 A query of awr_pdb_latch showed high waits for ' kokc descriptor allocation latch,' and a query of the mutex sleep history reported mostly mutex_type 'Row Cache' for location '[19] kqrpe'. 4 and later That said, there are a couple of bugs relating to dbms_stats & library cache locks. 2之后如果是密码错误导致的密码延迟一般产生的是library cache lock，这里发现有很多session username是空的，这就说明是那些登录异常的session，都是等待row cache lock，通过p1可以判断是dc_users组件。 latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Comentários sobre: BUG – High “row Cache Mutex” Waits – Oracle 19c Note: If the Oracle Database software is below Patchset Update 11. 1,458. But one question still remains: why Oracle 19c (and earlier versions as well which I haven’t checked) has both “latch: row cache objects” and “row cache mutex” wait events?An undocumented parameter could be there to mutexはビジーです。これは、mutexが排他モードで別のセッションに保持されているか、1つ以上のセッションによって共有して保持されているためです。mutexの排他権限を付与できるようにするには、既存のmutex保持側がmutexを解放する必要があります。 High waits on cursor: mutex X after upgrading the database to 12. A closer look at the row cache lock wait event. It was as if someone wanted to tell me that I was wrong in my last post ( Locks, Latches, latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Each row in this view contains statistics for one type of item kept in the library cache. 8 1 . Basically, we want to cache complex queries (involving multi-level views, sysdate, 'connect by level <= x' row generator, etc) and let the app invalidate when necessary. 1 Concurrency ~~~~~ 92%Mutex Sleep Summary ordered by number of sleeps desc Mutex Type Location Sleeps Wait Time (ms) Row Cache [17] kqrCreateUsingSecondaryKey 77,626,639 515,410,723 ; Hanganalyze output trace: 1. 0 and later Information in this document applies to any platform. 4 and also I found that dc 1. The AWR shows as ‘Waiting for event 'library cache lock' in wait class 'Concurrency'’. 2, 12. In particular if you have partitioned tables. 30719327: Global Hang Analyze and ASH shows hang chain as following, the waits on 'row cache lock' of node 1 were caused by the waiting on 'log file switch (checkpoint incomplete)' of node 2:. Hi Everyone, Recently, I was contacted by one of my friend who was battling with some performance issues, since they moved from 12c to 19c. latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log 从11. with query returns 63 rows in 12c and 65 rows in 19c: 31293791: e1pod: 31315441: imccust tpcds waited too long for a row cache enqueue lock: 31384324: fix for bug 31384324: 31395222: single session run, alter table online operation hangs for ever: library cache mutex x when insert run 2nd time from withing package: LUXOUG Comments on: BUG – High “row Cache Mutex” Waits – Oracle 19C If you share a representative query and the execution plan with row source level statistics (google that if you shared pool 75 0 5 61 7. 0 (12cR2), "row cache mutex" replaced 12. He was mostly strained about a particular problem with the new 19c database where he was getting excessive concurrency classed waits of “cursor: mutex X” (> 92% of the DB Time) and some “cursor: mutex S” events According to notes 9282521. gather_database_stats_job_proc ( )" in AWR and at the same time other SQL's 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 data dictionary tables. This was resolved by applying patch for a Bug 32356628 – Significant increase in library cache: mutex x wait time after upgrading database to 19c (Doc ID 32356628. x. Anyway, here is a brief explanation for each of these wait events: library cache: mutex X => related to concurrency. We can use it for The new 19c latch "SO private so latch" is positioned in LEVEL#=9, (J005) is waiting on 'row cache mutex' for 37 seconds, wait id 277 p1: 'cache id'=0xa, p2: 'where requested'=0x13, p3: ''=0x0 Blocked by Session ID 996 serial# 21988 on instance 1 which is waiting on 'latch: shared pool Library cache lock in wait class Concurrency In the Production Application we randomly notice a hiccup (slowness) in the database. Redo thread global enqueue. RT. A session may wait for this event when it is trying to get a mutex pin in Share mode but another session is holding the latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log row cache lock 35,677 35,644 0 0 133. Why do I see these KQR messages in the alert log? Resolving Issues Where 'Row Cache Lock' Waits are Occurring (Doc ID 1476670. 3. Row cache instance (A. 2 and Later) (Doc ID 2051456. row cache lock – Oracle Wait Event; enq: TM – contention – Oracle wait event; C. 5. TYPE. Further, p1 of the row cache lock wait holds the information about the cache id in the row cache. Huge version count is seen for the SQL statements during the problem period. 685In the latch statistics section,for library cacheGets 15934992misses 114277hit_ Resolving Issues of "Library Cache Pin" or "Cursor Pin S wait on X" (Doc ID 1476663. 1, backported to 11. 0 (12cR2), “row cache mutex” replaced 12. 0 (12cR1) and 11g “latch: row cache objects”, similar to “latch: library cache” substitution by “library cache: We are seeing the row cache mutex waits as one of the top wait events. 1 library cache: mutex X 117 0 2 16 11. Can you confirm that this is normal behavior? Can you suggest how to resolve these wait events? In Oracle 12. COUNT. 33 Foreground Wait Events latch: row cache objects 3,584,480 0 19,506 5 11. enq: TX - row lock contention. TABLE/PROCEDURE. 1) Last updated on SEPTEMBER 10, 2024. Detailed Description Mutexes are a lightweight method of serialising access to an object - in this case the library cache, ensuring that MOS "Bug 31135517 - High row cache mutex waits on hot objects - superseded (Doc ID 31135517. This action caused library cache lock, cursor: mutex S, and library cache: mutex X wait events when the cursor invalidations happens due to DDL on an object used in the SQL. Number of latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log RAC course guide page 7-3 states Single-instance oracle provides concurrency control through: - latches or mutexes for memory structures - enqueues for resource control - buffer cache pins for cache management In RAC, structures and resources may be accessed by or modified by a ssession running on any database instance RAC, therefore, requires 19c upgrade xoqu121. 19c sysdba cannot grant privileges to editioned objects if object belongs to another edition: 33525448: lnx64-19. Enter a title that clearly identifies the subject of your question. Applies to: In a 19c database experiencing high latch: cache buffer chains plus enq: TX - row contention with over 1400 connections which normally is lower around 200 connections. Changes There were no changes made to the database, nor any changes made to the insert statements. 2 to 19c, queries ran two times slower in 19c than they had in 12. 0 row cache mutex 70 0 1 21 7. High waits on latch free and row cache mutex wait events. 49. Mount/startup db primary/secondary instance. 1) Last updated on JULY 15, 2024. Latch contention troubleshooting approach 1. This problem affects all versions 19. Troubleshooting 'library cache: mutex X' Waits. 1, 18c or 19c. The most common cause of library cache mutex contention is excessive hard parsing caused by a failure to use bind variables in application code. CPU utilization spikes to 100% due to the mutex waits leading to database hang or application outage. g. 14. 72 52. I started looking at the event “ROW CACHE MUTEX” with a large number of events in 1 hour of process execution. Today, during an analysis of a performance problem in Oracle 19c, I found an event strange that I had not seen before. This job queue process was waiting on the library cache lock which was held by MMON_SLAVE. Oracle uses a least recently used algorithm to remove entries in the session cursor cache to make room for new entries when needed. Register: Don't have a My Oracle Support account? Click to get started! latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log When caching is used, then the dictionary cache (the row cache) is updated only once with the new high watermark, e. Although instance locks are mainly handled by LCK, some BUG - High "row Cache Mutex" Waits - Oracle 19c LuxOUG January 21, 2021 Article about BUG in Oracle 19c (English) See publication BUG 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 client can prevent other clients from accessing the same object The client can maintain a dependency for a long time (no other client can change the object). latch: shared pool. Subsequent parse calls will find the cursor in the cache and do not need to reopen the cursor. Each row cache lock will be on a specific data dictionary object. 1) Last updated on JANUARY 10, 2025. 17. The row cache mutex wait event (line 6) seems very interesting in this context, doesn’t it? Apparently, this is the one that protects the row cache now. 0 [Release 19] Oracle Cloud Infrastructure - Exadata Cloud Service - Version N/A and later HIGH LATCH FREE/ROW CACHE MUTEX ON KOKC DESCRIPTOR ALLOCATION LATCH (Doc ID 2749129. Applies to: Oracle Database Exadata Cloud Machine - Version N/A and later Oracle Cloud One more observation was related increased wait times for event ==> “library cache: mutex X”. 0. 0 (12cR1) and 11g “latch: row cache objects”, similar to “latch: library cache” substitution by “library cache: Oracle automatically resolves these waits by increasing shared pool by a small amount (16 MB = granule size) and shrinking db cache by the same amount. Top 10 Foreground Events by Total Wait Time LCK maintains all PCM locks, hashed or fine grain, and some of the non-PCM locks, such as row cache or library cache locks. 3 Concurrency Time Model Statistics sql execute elapsed time 36,014. 240716 35925654 [ROW CACHE] Sessions Deadlock on Row Cache Mutex and Shared Pool Latch; 35663882 [RMAN] Many Sessions are Blocked by CF Enqueue Contention; 36065162 [EXTENSIBILITY] C. 9 Concurrency SQL*Net more data to client 5,130,233 242. 18. gather_database_stats_job_proc ( )" in AWR and at the same time other SQL's latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log asdf Mutexes in Library Cache. 19c Database Hung due to High "row cache mutex" waits (Doc ID 2952129. Sometimes sessions are blocked by other session with "library cache lock" or "library cache: mutex x". 184. During our investigation into the root cause of the elevated shared pool latches, we uncovered interesting insights within the “Wait Event Histogram”. kksfbc child completion 3,367 162 48 . 8. "In other words, two or more sessions are trying to concurrently run the same statement (the latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log This cache is also called the row cache because it holds data as rows instead of buffers. DL. 13-rac,db hang at cpu or wait cpu<=log file switch row cache lock/mutex contention while adding user to db vault realm causes huge and service failures: 34472508: row cache mutex 6,478,228 809. SMON. 2. The mutex is busy because either the mutex is being held in exclusive mode by another session or the mutex is being held shared by one or more sessions. SM. Sessions attempting to online undo segments should show ktusmous_online_undoseg() in their call stack. Top 10 Foreground Events by Total Wait Time 23 %DB time is in Waiting Event for latch: row cache objects, with Wait Avg(ms) 46. DR. row cache mutex 63,032 385 6 1. 0 (12cR1) See Blog: row cache mutex in Oracle 12. 3 Concurrency direct path read 99,101 186. 4 Concurrency latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log A Row cache waits are waits against the Row Cache (or Dictionary Cache). 0 and later Oracle Database Cloud Exadata Service - Version N/A and later Gen 1 Exadata latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log After some time the library cache event was gone however i see the enq:HW – contention as the top event in AWR before flushing shared pool. when a caching of 20 is used and a nextval is requested the first time, then the row cache value of High amount of waits on Latch: Cache Buffer Chains and ENQ: TX - Row Lock Contention (Doc ID 3034758. (see Blog: Row Cache Object and Row Cache Mutex Case Study about Row Cache "BUCKET mutex"). Sequence number instance. BODY The session requests the mutex for a cursor object in exclusive mode, and it must wait because the resource is busy. latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log enq: TX - row lock contention. 139 row cache objects kqreqd exclusive 41 139 enqueue hash chains ksqrcl exclusive 36 139 shared pool simulator kglsim_chg_simhp_free Each library cache mutex protects one library cache hash bucket Known mutex types in 11g: Cursor Parent Cursor Pin This is more likely to be seen in an OLTP environment where both shared pool and buffer cache are in demand. 2, then waits on 'cursor: mutex X' will inadvertently appear as waits on 'cursor: mutex S', due to Bug 9591812. 485913. If on the other hand it is from a 4 hour sample, then it is insignificant. latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Oracle Database 19c Important Recommended One-off Patches (DOC ID 555. 1) Last updated on JULY 20, 2024. Waiting to retrieve the data from the remote cache for a DML operation. ; current - is for DML operations; cr - is for select operations; The difference between CR and Current is that CR requires a block with a given SCN, whereas current does not (current mode fetches the block latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log C. For example:- A package that is so hot (heavily accessed ) in library cache will be contended and the sessions appear to be waited on Library Cache: mutex X. 24. 85 (probably bigger than 10 ms CPU Scheduling time slice). txt, week after week, I am seeing the contention for lib. Database hang due to "library cache lock" and "library cache: mutex X" waits (Doc ID 2995666. 7. cache latch statistics. The SQL i specified independently. 1) Last updated on DECEMBER 27, 2023. Subordinate set number. MMON_SLAVE was a deadlock victim. As you can see Parse CPU to Parse Elapsd % is awful, most likely due to cursor: pin S wait on X. 172 and PINHITRATIO is only 0. 1. 2 latch free 7,869 5,132 0 0 29. 0 [Release 19] Information in this document applies to any platform. cursor cache. LCK handles PCM as well as non-PCM locks. PCTFREE and PCTUSED control whether Oracle will insert new rows in a block or not: latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Row cache ID number. Z = cache) DF. Contention on Latches and Mutexes that are of most concern to the DBA: ROW CACHE OBJECTS LATCH : REDOLOG BUFFER LATCHES : MUTEXES : References: My Oracle Support provides customers with access to over a million knowledge articles and a vibrant support community of peers and Oracle experts. Applies to: Oracle Database - Enterprise Edition - Version High "row Cache Mutex" Waits (Doc ID 2735198. Frequently, waits for 'Cursor: pin S wait on X' is a symptom and not the cause. 8 describing the patches, the enhancements should be used: When there is true contention on a specific library cache object. (Doc ID 1357946. 90 library cache: mutex X Library cache mutexes protect hash buckets within the shared pool. SID_HOLDING_MUTEX 220 大量session是220阻塞的，所以要通过ash裸数据看220会话的cursor: pin S wait on X参数是什么？如果也是220，则可能是死锁了！ 3、等待row cache mutex的参数 cachid：10，dc_users 8. Whenever a session wants to read or write into the library cache shared memory it needs to pin that object (cursor Here some tests in Oracle 19c (Note: Oracle 12. DX. Each hash bucket contains a number of cursors. Applies to: Oracle Database Cloud Schema Service - Version N/A and later Oracle Database Exadata Cloud Machine - Version N/A and later Oracle Cloud Infrastructure - Database Service - Version N/A and later Database hang or very slow performance with high contention on wait event 'row cache lock' in 12. The row cache is used to reduce IO to the data dictionary. 9 . More than 24 hours later other sessions start experiencing waits on 'library cache lock' and 'cursor: pin S wait on X'. 4 and later Oracle Database - Standard Edition - Version 8. DM. The SQL query result cache stores the results of queries and query fragments. But it could also be an uncommitted insert or update which has set the columns in the unique index to the same values trying. We observed a few instances of the “SGA: The locks on the data dictionary rows are called row cache enqueue locks. In Oracle 12. The problem will happen randomly and intermittently. PARAMETER. Applies to: Oracle Database - Enterprise Edition - Version 19. In this session, we will compose a new gdb script: "gdb_script_mutex_19c_body_lock_all" (see Appendix 7. lots of requests for mutex on user$ row cache, may hit Bug 30623138. The session is waiting on the mutex for the row cache. 11. Identify the session(s) experiencing problems Remember, databases don't have problems, only users, through database sessions 2. 8) We got a recommendation of increasing shared_pool value to fix this from Oracle. SUBORDINATE# NUMBER. After upgrading from 12. The mutex must be held in exclusive mode before any of the structures that it protects can be changed. 1) Last updated on NOVEMBER 03, 2024. As the snapshot portion of the row cache is effectively an extension of the row cache it self, other attributes of the cache are shared with the snapshot portion. System change number instance. NUMBER. 0 and later There are several possible symptoms here. @MartinKlierDBA – Resolving Child Cursor Issues Resulting In Mutex Waits Heavy - Oracle internal pitfalls II •DB Bugs like 10157392 + 12939876 (fixed in 12. In Mutex Sleep Summary I found a huge value of kkslce [KKSCHLPIN2] and kglhdgh1 64 (compared with values in a normal behaviour). 86 s 43. In one incident For first one we need to apply patch 28889389, which has the optimized code for cursor mutex while searching the parent cursor for the match, for second one 28794230, they High row cache mutex events occur when concurrently execute query with DBLINK by more than 10 job clients; From row cache id:15, row cache mutex contention occurs on 1. Oracle controls access to this and other areas of shared memory via a method called a 'mutex' (mutually exclusive). In this case, access to a specific cursor in Shared mode has been requested, but another session currently has an Lately, for some reason, I have started to come across the “cursor: pin S wait on X” wait event in the top 5 wait events in AWR reports. The item described by each row is identified by the value of the NAMESPACE column. In extreme examples the database can appear to hang and you may receive related timeout symptoms such as "WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK!" 19c Database Hung With ORA-04022 Errors and High Row Cache Lock Waits During Heavy Load (Doc ID 3043192. Top 10 Foreground Events by Total Wait Time. Waiter session, ====. This lock is Comecei a olhar o evento “ROW CACHE MUTEX” com uma grande quantidade de eventos em 1 hora de execução de processo. Podemos ver acima em 1 hora de processamento que tivemos 2. In the body, insert detailed information, including Oracle product and version. 3) C. A session may wait for this event when it is trying to get a mutex pin in Share mode but another session is holding the mutex pin on the same cursor object in exclusive. 8 and 9239863. 7 . datafile instance. To view full details, sign in with your My Oracle Support account. The existing mutex holder(s) must release the mutex before the mutex can be granted exclusively. 3 User I/O TX contention usually happens because there's an uncommitted update to the same rows. In an Oracle 12. Login or connection storm is observed during the problem. latches are a type of lock, a serialization device, a mutual exclusion device. 96ms 92. 8)" describes that the fix implements 'hot object cloning' to alleviate row cache mutex contention. 3 db file sequential read 15,594 0 0 0 58. SN. Mutexes or mutual exclusion algorithms are lighter and more granular concurrency mechanism than latches and are used in concurrent programming to avoid the simultaneous use of a common resource. Property Description Parameter type Integer Default value 50 Recommended values 400 2022-06-20 09:20:20 row cache mutex 26 cursor: pin S wait on X 32 library cache: bucket mutex 36 latch: shared pool 40 2022-06-20 09:20:30 library cache load lock 46 latch: shared pool 50 library cache: mutex X 59 cursor: pin S wait on X 61 row cache mutex 62 latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Detailed Description . Applies to: Oracle Database Cloud Schema Service - Version N/A and later Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later Oracle Cloud Mutexes are lightweight methods of ensuring serialisation of access. 1) for Linux 19. 9 2 . This event indicates that the requested current buffer was transferred from another instance in the cluster, and 2 network hops were involved in the request. enqueue locks (both shared and exclusive) are the same thing. What is a 'Cursor: pin S wait on X' wait? A cursor wait is associated with parsing in some form. Oracle started using mutexes from 10g for certain operations in the library cache but from 11g all library cache latches were replaced by mutexes which lead Troubleshooting Databases Hang Due to Heavy Contention for 'library cache: mutex X' Waits (Oracle 11. The mutex must all of them except the one that successfully acquired all necessary locks/pins on the library/row cache entries, latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log library cache lock 6,305 1,153 183 3. The row cache lock was held by a job queue process, which was gathering statistics. latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Library cache latch contention Tom,In my report. The enqueue lock structures are allocated from the shared pool as needed but when these requests wait and time out, we see the row cache lock wait event. 0 log file CURSOR : pin S CURSOR : pin X CURSOR : pin S wait on X CURSOR : mutex S CURSOR : mutex X Library cache : mutex X Mutexes are similar to locks except that they lock object in shared memory rather than rows in tables and indexes. 1 Concurrency latch: ges resource hash list 529,983 412 1 . 0 (12cR1) and 11g “latch: row cache objects”, similar to “latch: library cache” substitution by “library cache: mutex X” in the previous release. The Cache Fusion protocol guarantees that requests are fulfilled in 3 hops or less, regardless of the number of instances in the cluster. Row locks primarily serve as a queuing mechanism to prevent two transactions from modifying the same row. The mutex must all of them except the one that successfully acquired all necessary locks/pins on the library/row cache entries, This can lead to high 'latch: row cache objects' contention may be seen on DC_ROLLBACK_SEGMENTS together with high 'enq: US - contention' waits when using system managed undo with an auto tuned undo retention period. There were some SQL with high execution rate observed which were creating a new child cursor for every execution and the version count report showed high version counts with the following 'library cache lock' Waits: Causes and Solutions (Doc ID 1952395. 0 ) At first we list all kqr* functions: SQL > select value from nls_database_parameters where parameter = 'NLS_CHARACTERSET'; latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Additionally, an object cannot be aged out of a cache until the mutex reference count is 0. Event Waits Time(s) Avg wait (ms) % DB time Wait Class library cache lock 2,356,438 64,073 27 71. Sign In: To view full details, sign in with your My Oracle Support account. 5K 124. Applies to: Oracle Database - Personal Edition - Version 8. In RAC wait event names: gc denotes the Global Cache service. 1. " Oracle states: "A session waits on this event when it wants to update a shared mutex pin and another session is currently in the process of updating a shared mutex pin for the same cursor object. 87 library cache: mutex X Library cache mutexes protect hash buckets within the shared pool. 8 Today, during an analysis of a performance problem in Oracle 19c, I found an event strange that I had not seen before. VARCHAR2(11) Parent or subordinate row cache type. Column statistics. The mutex must all of them except the one that successfully acquired all necessary locks/pins on the library/row cache entries, latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log What is a 'Cursor: pin S wait on X' wait? A cursor wait is associated with parsing in some form. A shared lock is just a lock that more than one thing can hold at the First, let me offer a little explanation about the wait event "cursor: pin S. 5 0 . This is a RAC wait. 1) Last updated on DECEMBER 24, 2024. 9 new introduced subroutine "kqrScan" (called by kqrpre or kqrpre2). 2 0 1. 2022-06-20 09:20:20 row cache mutex 26 cursor: pin S wait on X 32 library cache: bucket mutex 36 latch: shared pool 40 2022-06-20 09:20:30 library cache load lock 46 latch: shared pool 50 library cache: mutex X 59 cursor: pin S wait on X 61 row cache mutex 62 This session waits on 'row cache lock', this is expected behaviour. The mutex must all of them except the one that successfully acquired all necessary locks/pins on the library/row cache entries, latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log A RAC Global Cache Fusion wait. The database Library cache mutexes protect hash buckets within the shared pool. latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log Detailed Description . 8 2 . 84 28. AWR report. In Trace Files, we can also see the 19. High wait time on row cache mutex and latch: shared pool. 34 db file sequential read 4,351,598 0 7,070 2 A library cache operation is being performed and Oracle is trying to get the library cache mutex in eXclusive mode. The server result cache is a memory pool within the shared pool that contains the SQL query result cache and PL/SQL function result cache, which share the same infrastructure. The row lock exists until the transaction commits or rolls back. VARCHAR2(32) Name of the initialization parameter that determines the number of entries in the data dictionary cache. The snapshot portion of a row cache may be larger (may contain more rows) or smaller (may contain fewer rows) than the live portion of the row cache. 4 Network cursor: mutex X 330,249 192. 2. Direct loader parallel index create. 22. I am getting library cache lock event for SQL ID "dbms_stats. In lib cache latch statistics, the SQL AREA GETHITRATIO is only 0. 9 %DB time is in Waiting Event for library cache: mutex X, with Wait Avg(ms) 10. 1 refresh controlfile command 17,230 0 0 0 64. Event Waits Total Wait Time (sec) Avg Wait % DB time Wait Class row cache lock 1,212 112. 0 direct path read temp 11,789 0 1 0 1,178. 1) Last updated on APRIL 17, 2023. 2 1795 0 12 rows selected. The respective SQL statement is one of the frequently running statement (15,000 times per minute) in the application. 1) Last updated on DECEMBER 31, 2024. 6 Other cursor: pin S 933,128 227 0 . 5) to trace both kglGetMutex and kglGetBucketMutex on all mutexes triggered by kglLock on PLITBLM Body. The row cache lock is used primarily to serialize changes to the data dictionary and is waited on when a lock on a data dictionary cache is required. 882 eventos com latch: row cache objects; latch: session allocation; latch: shared pool; latch: undo global data; library cache: bucket mutex X; library cache load lock; library cache lock; library cache: mutex X; library cache pin; library cache shutdown; local write wait; lock manager wait for remote message; log buffer space; log file parallel write; log library cache: mutex X 2,242,811 769. Hang Manager correctly identified session 11909 as Final Blocker, this is shown in dia0 LWS trace files. Failing to obtain the mutex will result in a library cache: mutex X wait. if High waits on “row cache mutex” when looking up user or role information in user row cache (dc_users). 5 . ndob kxn xppoi shcni hxukrgn ibqg lznmx obghge ueduhpy tipx