Hana Data Structure has two components namely Main Storage & Delta Storage.
|Data Structure||Access Pattern||Compression|
|Main Storage||Optimized for read access||Advanced|
|Delta Storage||Optimized for write access||Basic|
- Read operations are performed on both structures, while write operations only affect the delta.
The main storage contains the main part of the data (data compression).
Write operations on compressed data in the main storage would however be costly. Therefore, write operations do not directly modify compressed data in the main storage. Instead, all changes are written to a separate data structure called the delta storage.
The delta storage structure itself exists only in memory and is not persisted to disk.
Delta merge Operation
The purpose of the delta merge operation is to move changes collected in the delta storage to the read-optimized main storage.