Change log table delete u0096 datamart delta works?

[Former Member]

Hello BW Experts,

Data comes from Source system to ODS and then to the Cube. ODS is used from a long time ( 6 years ). And the change log is huge. We are contemplating on deleting the ODS change log. If the delta load from ODS to Cube ( Datamart )is based on the change log, deleting it would disable the delta capability???

Suggestions appreciated.

Thanks,

BWer

[edwin_harpino]

hi BWer,

deleting change log won't disabled the delta capability, but you should delete the change log for data that not change anymore (old data) since delta/changes to infocube based on change log. hope this helps.

[Former Member]

Hi dear,

there is an OSS Note that describes what you want to know...

643880 'Background Information Deleting Data from Change Log'

"Changelogs help to make ODS DataSources delta capable and are stored as a PSA table (indeed the Changelog is the PSA-Table of the Export-DataSource of the ODS !)

Deleting data from the Changelog of an ODS object is allowed if these requests, which are no longer required for the delta update and also are no longer used for an initialization from the Changelog, have already been loaded into further DataTargets.

Since the Changelog data can become extremely large, you may want to reduce the amount of data volume and delete data for a specific period of time as part of your data management strategy. As your ODS objects grow, Changelog files also grow (approximately by a factor 2). It is recommended to retain temporary, limited history according to your business needs.

Note: Deciding not to purge Changelogs files before an upgrade can have a negative impact on the runtime of the Alpha Conversion phase. Runtime of the upgrade can increase because the conversion process has to read all ODS objects along with their associated Changelogs.

Points to be Aware of Before Deleting Changelogs:

***You cannot reprocess old delta requests

Once you delete Changelogs, the PSA request (ODSR_... requests), which are generated in the PSA when the request is activated in the ODS and contains the delta information, will no longer exist. Therefore, you will not be able to reload any old delta requests that are associatedwith the Changelogs which were removed from the system.

***New data targets cannot be built from the change log

If Changelogs do not exist, new data targets can be created but will be built from the ACTIVE table using "FULL Upload" method but it is not recommended because this option has not gone through a complete testing cycle. Therefore, SAP cannot 100% guarantee the integrity of the data in all data loading scenarios.

***Rebuilding of ODSR_... Requests

If you delete the Changelog then rebuilding from the Changelog is also no longer possible for the deleted requests.

***You can no longer rollback the activated requests from the ODS object"

Hope it helps!

BYe,

Roberto

[former_member188975]

Hi,

Deleting the ChangeLog will not disable the delta functionality. It is a common practice. Delta load is based on the Changelog, but the entries originate from ODS data activation.

Also see:

http://help.sap.com/saphelp_nw04/helpdata/en/6d/1fd53be617d524e10000000a11402f/content.htm

Hope this helps...