Docstoc

SAP Note 552289

Document Sample
SAP Note 552289 Powered By Docstoc
					          SAP Note 552289 -      FAQ: R/3 Lock management

Note Language: English          Version: 4 Validity:    Valid Since 06.02.2009


Summary

Symptom
This note contains answers to frequently asked questions (FAQ).

More Terms
Lock management, lock table, enqueue, enqu/table_size

Cause and Prerequisites


Solution
[1] Question: How large can and should the lock table be configured?
[2] Question: What does the started wait time in the syslog mean for
           locks?
[3] Question: How does communication take place in lock management?
[4] Question: What are "black" and "blue" locks?


[1] Question: How large can and should the lock table be
configured?
As of Release 4.0, the default size for the lock table is 4 MB. This value
is sufficient for medium-sized systems. As of Release 4.6, it becomes
apparent that a size of 10 to 20 MB is required for some background jobs,
and a size of 32 to 200 MB may be required for large systems, but this is
the exception. Since a lock table that is too small causes transaction
terminations, but the resources for the lock table are relatively low, you
should initially specify a size of 20 MB. In general, no further changes to
the layout of the shared memories are required when you use this size
(except for AIX 32-bit). You can make this setting by using the profile
parameter: enque/table_size = 20000
You can monitor the lock table in transaction SM12 by choosing the menu
option "Extras -> Statistics".
The lock table is a shared memory, not a database table.


[2] Question: What does the started wait time in the syslog
mean for
           locks?
Usually, locks can be set in the R/3 system only if they are available. If
an object is already locked, the system rejects lock requests and issues
the error message " ... locked by user ...". This prevents deadlock
situations, which you may be familiar with in databases. However, a job
should not terminate in background processing if a lock is unavailable at
that moment. In this case, the system requests the locks with the addition
"and wait". The wait time incurred is then logged in the syslog. You can
use the profile parameter enque/delay_max to set the maximum wait time.


[3] Question: How does communication take place in lock
management?
This question is especially important for troubleshooting because it
indicates where errors may occur. In the central instance, all work
processes can access the lock table directly. Therefore, the ENQ work
process is not required, and no communication takes place.

29.09.2009                                                        Page 1 of   2
           SAP Note 552289 -      FAQ: R/3 Lock management

An application server sets and deletes locks via the message server.
Therefore, communication takes place as follows: work process -> dispatcher
-> message server -> dispatcher -> ENQ work process. The lock table is read
using RFC, that is: work process -> gateway -> gateway -> dialog process.
In this case, the ENQ process is not used either. However, central
instances with few dialog processes may be overloaded quickly because
dialog work processes are required for RFC communication accordingly. The
same also applies to pure background servers or update servers. Therefore,
the number of dialog work processes must always be at least as high as the
number of remaining processes.


[4] Question: What are "black" and "blue" locks?
Black locks are normal transaction locks. Blue locks are inherited by the
update system and are deleted with the corresponding update request. Blue
locks are also saved in the file system and are restored when the system is
restarted.



Header Data
Release Status:              Released for Customer
Released on:                 24.02.2009     10:36:52
Master Language:             German
Priority:                    Recommendations/additional info
Category:                    FAQ

Primary Component:      BC-CST-EQ Enqueue




The Note is release-independent




Related Notes
 Number       Short Text
 1118297      XI runtime: QRFC processing of messages
 923610       Memory param recommendations for Bank Analyzer 4.2 and 5.0
 852524       Deletion of reservations from APO




29.09.2009                                                       Page 2 of   2