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Triggering a Delta Merge (When Using the SAP HANA Database)Locate this document in the navigation structure

Use

If you are using an SAP HANA database, data modifications are initially saved in a delta storage that is optimized for write access. However, most of the data is saved in a highly compressed format in the main storage, which is optimized in terms of required memory space and read performance. A delta merge is used to transfer modifications from the delta storage to the main storage. First, an asynchronous check is performed for see whether a delta merge is required. If a threshold value is exceeded, the merge is carried out in the delta storage. When a read access is executed, the data is read from the main storage and the delta storage and the results are merged together.

Procedure

The check and the delta merge - if data has been changed during Data Warehouse load processes - are either performed automatically by the system or must be triggered manually. This depends on the relevant object type:

Object Type

Delta Merge

Standard DataStore Object

SAP HANA-Optimized DataStore Object

After activation, an automatic check is run to see whether a delta merge can be performed. This also applies to DataStore objects that belong to a semantically partitioned object.
 

Persistent Staging Area (PSA)

After data has been written to the PSA, an automatic check is run to see whether a delta merge can be performed.

Write-Optimized DataStore Object

Standard InfoCube

SAP HANA-Optimized InfoCube

The check and the delta merge are not performed automatically. This also applies to objects that belong to a semantically partitioned object.

The data transfer process (DTP) has an Update tab that contains the Trigger Delta Merge checkbox. This controls the delta merge, once the DTP request has been processed. This checkbox is selected in the default setting.

Note

In certain exceptional cases, performing a delta merge after processing a DTP request is not recommended, due to load balancing issues. In cases like this, we recommend deselecting the checkbox in the DTP and using the Trigger Delta Merge process type to trigger the delta merge. For example, data from multiple sources is loaded into an object. The delta merge check is only performed at the end of the entire loading process.

If you use process type Trigger Delta Merge, proceed as follows:

You are in the plan view of the process chain where you want to include the process. Process type Trigger Delta Merge is available in process category Load Process and Post-Processing.

  1. Drag and drop process type Trigger Delta Merge to a suitable position in the process chain.

  2. A dialog box appears. To create a new process variant, choose Create.

  3. In the next screen, enter a name and a description for the process variant and choose Continue.

  4. On the process variant maintenance screen, specify the type and name of the object for the delta merge.

  5. Save your entries and return to the plan view for the process chain.

  6. Link the process to the required loading processes.

More information: Creating Process Chains.

Note

Make sure that the DTP or process type always triggers a delta merge. If no delta merge takes place, the data remains in delta storage. Over time this will result in storage problems and have a negative impact on read performance.