SAP Basis Tech Supports

Symptom

A dialog process holds semaphore 16. Transaction SM50 or SM66 or program dpmon display Other terms

TABL
Reason and Prerequisites

After a certain number of buffer accesses, a check is performed to determine whether an asynchronous buffer reorganization or a suppression run should be carried out. The criteria are as follows:
Less than 3% of free directories or free space is available orthe buffer quality measured as GRC/(GRC + GMC) since the last reorganization or suppression is less than 95%. GMC represents the number of buffer accesses that could not be processed using the buffer. GRC is the total number of buffer accesses.

If one of these criteria is met, an ADM message asks the dispatcher to asynchronously start the reorganization or suppression in a free dialog work process. The actions are carried out under semaphore protection.
The asynchronous suppression first releases all objects that have the status "loadable", "absent" or "error". If the space available is subsequently still insufficient, the system releases objects that have not been accessed for a long period of time. Then the suppression quality is calculated. Depending on the result, later suppressions may not be performed.
The asynchronous reorganization tries to reduce the buffer fragmentation. The reorganization is carried out incrementally.
The profile parameters zcsa/exchange_mode and zcsa/reorg_mode determine whether an asynchronous suppression or reorganization is performed at all. Both parameters are set to the value "on" by default.
In transaction AL12, you can choose "Utilities->Time Measurement->Generic Key Buffer” from the menu to switch the time measurement for the asynchronous actions on or off. The times are written into the developer trace of the work process that performs the asynchronous action, for example:
B dbtbxdispl: Displ: Phase 1 >10798 msec<
or
B dbtbxdispl: Reorg: Phase 3 >26 msec<

Solution

After consulting SAP, you can deactivate the automatic suppression of the table buffer in individual cases if this is justified. To do this, set the following profile parameter:
zcsa/exchange_mode = off
You can also use the parameter in the default profile.