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Use

 <region_name>: collision rate (<percentage>%), <number_of> collisions, <number_of> accesses on region <region_ID>


Explanation

The rate of lock collisions is high. Tasks that run in different threads are attempting to access a global storage area in parallel. The synchronization required for this often leads to an increased collision rate.

Note:

One exception to this in SAP liveCache databases is high collision rates in the OMSVDIR and CNSTVIEW regions (<region_id>). This is normal for certain actions, such as a simultaneous CIF queue transfer.


User Response

 You need to act if the collision rate rises above 10%. Generally, the risk of collisions rises with the number of processors used (MaxCPUs general database parameter). In multiprocessor systems, you should therefore check whether the database system can fulfill the needs of the applications with fewer CPUs.

If high collision rates occur in multiprocessor central systems (database system and application running on the same computer), check whether the computer's CPU is overloaded, and whether the database threads are blocked by other applications. In this case, the database threads containing user tasks should have received REAL TIME PRIORITY in the operating system. To avoid operating system blocks however, the value of MaxCPUs must be at least one lower than the number of actual CPUs.

More Information

Relevant  DB-Analyzer Files
Helpful with ...
DBAN_REGIONS.csv Information about accesses to critical sections
DBAN_RW_LOCKS.csvInformation about accesses to critical sections (reader-writer locks) 

 

 

SAP Note
Helpful with ...
1681336 - SAP MaxDB: Synchronization objectsFind more information about the use of reader/writer locks.
1680854 -  Database Analyzer: LOGQUE<nr>: collision rate ...Note explains how this DB-Analyzer file can be used to interpret collision rates on log queues. 
1153461 - Altering MaxDB task schedulingDescribes relevant parameters to influence region use.
Expert Sessions (Link to trainings)
Content / Helpful with ...
Session 27: SAP MaxDB Multi Tasking Description of "cooperative" multi-tasking and how tasks interact 
Documentation (links)Helpful with ...

Database Administration
General Database Parameters, Traces

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