on 11-23-2013 1:24 PM
What is delta merge in HANA?
Hi Rohit,
As HANA is a Column based In Memory database, and in this each column is divided into two parts:
Dictionary Encoding and Attribute Vector.
Dictionary Encoding stores only unique records in sorted way and their sequence number as Implicit Value ID
While Attribute Vector records position of all the records and their corresponding Implicit Value ID.
Because of this write operations in Column Store are very expensive.
So to overcome this SAP introduced the Concept of Delta Storage also called differential buffer.
In HANA, both Main Storage and Delta Storage are used for read operations.
But write operations are performed only on Delta Storage.
So any new record that you enter is written and stored in Delta Storage.
After sometime we merge Main Storage and Delta Storage so that Main Storage has all the records.
This merge process is called Delta Merge
To learn more please see the video tutorials at OpenSAP:
https://open.sap.com/courses/1/wiki/welcome?module_item_id=55
Also refer to the following guide for different Merge types available in HANA:
http://scn.sap.com/docs/DOC-27558
Regards,
Vivek
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