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DELTA merge is an operation to move the data from WRITE optimized DELTAmemory to READ optimized and Compressed MAIN memory. This can be done automatically by HANAusing Smart Merge technology or manually using MERGE DETLA OF sql statement or using right click option on HANA studio.
The Delta Merge Operation is an operation on a table column store data structure.
The purpose of the delta merge operation is to move changes collected in the delta storage to the read-optimized main storage.
After the delta merge operation, the content of the main storage is persisted to disk and its compression recalculated and optimized if necessary.
A further result of the delta merge operation is truncation of the delta log (ie redo operations)
It is important to understand that even if a column store table is unloaded or partly loaded, the whole table is loaded into memory to perform the delta merge.
During the delta merge operation, every partition of a partitioned table is treated internally as a standalone table with its own data and delta store.
