SAP Note 24879 - Cluster: Trashing effect with Client copy

Symptom:

Client copy using R3trans or RSCLICOP uses a lot of time to copy a logical cluster table (for example CDPOS), without obviously getting anywhere.
By using trace, you can see that the process repeatedly
(1) Reads the physical records to a certain cluster record of the
source client
(2) Writes the physical records to the corresponding cluster
record of the target client
(3) Reads the physical records to the cluster record of the
target client
(4) Starts again at point (1)
However, this is not an infinite loop: After a certain amount of time, the process will continue with the other cluster records.

Cause and prerequisites

The cluster interface can retain a maximum of 20 cluster records in parallel in its own main storage buffer. A memory representation of a cluster record consists of 32K pages. There is a limit of 100 pages. If this limit is exceeded when importing a cluster record, cluster records are rejected from the main storage buffer until it either goes below the limit again, or until only the current cluster record remains. This discarding of a cluster record means that, if the record was changed, it is written back to disk.

For client copy, a 'Trashing effect' can occur if a cluster record contains a lot of records of a logical table and fills more than fifty 32K pages of memory. At the point where the total of initial and target cluster records in the main memory pages exceeds 100, these records will be alternately replaced from the main storage buffer:
(1) The next logical record from the source client should be read
=> The cluster record must be imported
=> The target cluster record is replaced and written
(2) The logical record should be stored with new client
=> The target cluster record must be imported
=> The initial cluster record is replaced
and so on until all logical records of the initial cluster record are processed. This then continues with the next initial cluster record (where the same problem can also occur).

Solution
Corrected with B11K016645 (2.2G)
Corrected with BINK072025 (3.0B)
If required, a patch can be created extremely easily (see "repairs in the program code")

Additional key words

Clusters, CDCLS, CDPOS, Client copy, RSCLICOP, performance