What is a library cache lock?
The library cache lock controls the concurrency between clients of the library cache by acquiring a lock on the object handle so that one client can prevent other clients from accessing the same object or the client can maintain a dependency for a long time (no other client can change the object).
How do I know which session is holding a particular library cache lock?
Open the tracefile and do a search for “PROCESS “. In the process section, search for the wait event by doing a search on ‘waiting for’. Use the ‘handle address’ to find the process that is holding the lock on your resource by doing a search on the address within the same tracefile.
How do I resolve row cache lock?
The solution to excessive row cache enqueue lock waits is: 1 – Serialize the DDL running on a small number of concurrent DDL tasks. 2 – If the row cache enqueue locks are for dc_sequences, consider using DBMS_SHARED_POOL. KEEP to pin your sequences.
What is library cache pin in Oracle?
Library cache pin (%) Library cache pins are used to manage library cache concurrency. Pinning an object causes the heaps to be loaded into memory (if not already loaded). PINS can be acquired in NULL, SHARE or EXCLUSIVE modes and can be considered like a special form of lock.
What causes Library cache lock?
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. 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.
What is the use of library cache?
The Library Cache is a piece of memory within the SGA that Oracle uses in order to store SQL Statements. Whenever a Process issues an SQL Statement, the text of the Statement goes into the Library Cache where the statement is parsed an validated.
What is row cache?
In order for DDL (Data Definition Language) to execute, it must acquire a row cache lock to lock the data dictionary information. The shared pool contains a cache of rows from the data dictionary that helps reduce physical I/O to the data dictionary tables and allows locking of individual data dictionary rows.
What is row cache lock wait?
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. Waits on this event usually indicate some form of DDL occuring, or possibly recursive operations such as storage management and incrementing sequence numbers.
What is concurrency wait time Oracle?
CONCURRENCY_WAIT_TIME : Concurrency wait time (in microseconds) Microsecond is to one millionth of a second so it should not cause significant delays, it is internal Oracle synchronisation mechanism based on i.e. latches, it is very simple and fast.
What is concurrency wait event in Oracle?
The library cache pin wait event is associated with library cache concurrency. It occurs when the session tries to pin an object in the library cache to modify or examine it. The session must acquire a pin to make sure that the object is not updated by other sessions at the same time.
What is row cache lock in Oracle?
What is buffer busy waits in Oracle?
The buffer busy wait event happens when a session tries to access a block in the buffer cache but it can’t because the buffer is busy, because another session is modifying the block and the contents of the block are in flux.
Why are library cache lock and pin waits needed?
Library cache lock and pin waits can hang instance, and in few cases, whole clusters of RAC instances can be hung due to library cache lock and pin waits. Why Library cache locks are needed? Library cache locks aka parse locks are needed to maintain dependency mechanism between objects and their dependent objects like SQL etc.
What is the Oracle library cache load lock?
Oracle library cache load lock tips. 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. The loads of SQL statements are serialized and locked in exclusive mode,…
How to troubleshoot library cache lock in AWR?
Analyzing AWR in the “SQL ordered by Elapsed Time” topic we can check the SQLs that have the most waits from the event cache lock lock and killing those SQLs will not resolve the contention, I say that for sure, because I tried it. Analyzing AWR in the “SQL ordered by Sharable Memory” topic also does not show the offender.
What causes library cache lock contention in SQL?
Cause: By analyzing HANG ANALYSIS, it was possible to identify Session 4102 by running SQL Analyzer possibly a Tuning Advisor from 02/20/2018 at 10am and was causing library cache lock contention. Below the SQL that Session 4102 was running: