Purpose of this document is a number of frequently asked database performance questions for all oracle dbas. Hello, the database on one of 4 nodes started to hang. A row cache enqueue lock is a lock on the data dictionary rows. Oracle 11g clients can also connect to oracle 10g servers. Deadlock and resulting waited too long for a row cache enqueue lock. My starting point on library cache locks has always been this oracle support document. If the state is not waiting then they are not waiting, they are using or trying to use cpu. Below is a summary from one of my favorite metalink notes. The load lock is always obtained in exclusive mode, so that no other process can load the same object.
When a particular row is being modified by the process, either through update delete or insert operation, oracle tries to acquire lock on that row. On a similar fournode oracle rac cluster with oracle. As of oracle 10g, event 942 and event 10035 can be set to report sqls that fail during parse operations. Managing sequences in a rac environment the blog from. A rather odd performance issue happened at work a few days ago. This is because the library cache and the row cache are global in raccausing the row cache lock wait to be more pronounced. Another method to find the session holding library cache lock is described here. Helps reduce physical io to the data dictionary tables allows locking of individual data dictionary. The o10 database interface allows you to connect to oracle 10g servers using oracle 10g database client or oracle 10g instant client. Library cache lock oracle wait event oracle database. Resolving a library cache lock issue oracle study notes. If for some reason you cant use a sequence, just perform an update on that row.
Supported versions for oracle connecting to your database. If you are configuring cache connect to oracle for use with rac, use one of the following oracle client releases. Any process that is blocking others is likely to be holding one of these locks. Database hangs periodically with many sessions being blocked by each other, deadlocks can be seen as well, with different waits such as cursor. Real life rac performance tuning arup nanda lead dba starwood hotels. So, before parse locks on a library cache object can be broken, library cache pins must be acquired in exclusive mode and then only library cache objects can be dropped. Multiple tables are used to provide scalability each log source inserts into a dedicated table. When a row in oracle gets locked, the record itself is updated with the new value if any and, in addition, a lock which is essentially a pointer to transaction lock that resides in the rollback segment is placed right into the record. Real life rac performance tuning new york oracle user. Using oracle database 11g release 2 result cache in an. Its quite possible its application related, but im just trying to determine the actual cause now. Oracle will lock that row until you end your transaction commit or rollback and all other updates will wait until the lock. Does anyone have some insights as to the root cause and what to do for a troubleshooting. This application uses direct path inserts and bypasses the cache so i can see that it also scales in rac 10g rac, 6 nodes.
How to find which session is holding a particular library cache lock doc id 122793. Ask tom library cache lock for wrong passwords oracle. In exclusive mode, the foreground process will try to get the lock. Troubleshooting row cache enqueue locks check out mos document id 278316. Only when the process has acquired lock the process can modify the row otherwise the process waits for the lock. Release notes for oracle timesten inmemory database 7. Oracle database 12c release 2 support lessons learned from early adopters wrote.
The alert log file indicates waited too long for a row cache enqueue lock. This issue occurs when the database detects that a waiter has waited for a resource for longer than a particular threshold. The loads of sql statements are serialized and locked in exclusive mode, such that only one process can load an object or a piece of an object at a time. 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. If the load lock is busy the session will wait on this event until the lock becomes available. Janet bacon, mike ault, madhu tumma, murali vallath, randy. Oracle says that if the query returns less than 40 percent of the table rows in an ordered table or seven percent of the rows in an unordered table, based on the index key value described by. Row cache enqueue lock tips burleson oracle consulting. 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. Varchar22 type of user or system lock the locks on the user types are obtained by user applications. The locks on the data dictionary rows are called row cache enqueue locks. The library cache load lock oracle metric occurs when the process is waiting for the opportunity to load an object or a piece of an object into the library cache.
See oracle support articles potential reasons for waited too long for a row cache enqueue lock. The row cache holds the data dictionary entries in the shared pool. Posts about gc buffer busy written by riyaj shamsudeen. Longtime oracle dba april 2226, 2012 mandalay bay convention center las vegas, nevada, usa. What are oracle row cache lock waitspart 1 to execute, ddl data definition language must acquire a row cache lock to lock the data dictionary information the shared pool contains a cache of rows from the data dictionary. The session tries to find the load lock for the database object so that it can load the object. Oracle row cache lock wait event in rac environment.
Lobs from oracle database 10g and prior releases are still supported and will now be referred to as basicfiles. Unlike some databases, which use a lock manager to maintain a list of locks in memory, oracle database stores lock information in the data block that contains the locked row the database uses a queuing mechanism for acquisition of row locks. All of a sudden, one of the databases started to work very slowly, and a quick look in ash data showed that it was spending over 70% of its time waiting on row cache lock not to be confused with latch. Oracle s locking concept is quite different from that of the other systems. Increasing active sessions and a contention in the database with the event library cache lock wait class concurrency lets go to troubleshooting now lets investigate the awr. The message waited too long for a row cache enqueue lock. April 2226, 2012 mandalay bay convention center las vegas.
The row cache lock escalates into the row cache enqueue lock when multiple ddl statements are waiting to execute. The enqueue will be on a specific data dictionary object. The compilation of package will hang on library cache lock and library cache pin if some users are executing any procedurefunction defined in the same package. If a session is executing an sql, then library cache pins will not be available and there will be waits for library cache pins. Row cache hints and tricks with a number of sites running row cache in production, oracle has gained some significant experience in running oracle rdb systems with the row cache feature. In 10g password management and thus the applied locks were done in in row cache but in 11g it changed to library cache. Oracle database cloud exadata service version na and later information in this document applies to any platform. Jonathan lewis have another look at these sessions with event row cache lock. Each row cache lock will be on a specific data dictionary object. The library cache lock controls the concurrency between clients of the library cache by acquiring a lock on the object handle so that either. It is used primarily to serialize changes to the data dictionary and to wait for a lock on a data dictionary cache. Library cache lock scripts for rac bobby durretts dba blog.
If the lock wait exceed a predefined threshold, the ddl will abort and cause a. This fix affects both client and server, so the fix needs to be applied on both client and server. Oracle database row locks tx gerardnico the data blog. Oracle maintenance data consistency with the help of locking mechanism. Oracle 11gr2 single session library cache pin library cache lock cycle recently we observed a single session library cache lock cycle deadlock when upgrading to 12c 12. If the lock wait exceed a predefined threshold, the ddl will abort and cause a trace file to be generated. Identifier for session holding or acquiring the lock. Database performance faq diagnostics part extractread. About me oracle dba for 16 years and counting speak at conferences, write articles, 4 books, provide trainings, security audits. When a session waits on the read by other session event, it indicates a wait for another session to read the data from disk into the oracle buffer cache. The library cache lock wait is seen due to the fact that the account status gets updated internally due to incorrect login and is maintained in the library cache. While running the oracle universal installer on a unix platform to install oracle database 10g software, you are prompted to run orainstroot. And below is the full content of the note database performance faq investigating a database performance.
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