Query on SQL Script - HANA Basics

[Former Member]

Hi

While practicing the Tutorial ,I came across below SQL statement,can any body explain what this statement exactly does or any pointers to understand the after effects of execution of the below statement would be helpful.

UPDATE "EFASHION_TUTORIAL"."SHOP_FACTS" MERGE DELTA INDEX

Thanks

Santosh

[lbreddemann · Accepted solution]

Hello Santosh,

the column store tables are highly read optimized data structures internally.

Unfortunately, these data structures are not so well suited for changing data in them.

To overcome this every column store table has a so called delta log that allows to capture data changes like update, insert and deletes in a very fast manner.

The problem here is just that the delta log in turn is not so well performing during read operations as the main structure is.

So, what's needed here is to get the data from the delta log to the so called main index.

This is what a delta log merge operation does.

The command you mentioned triggers this merge operation for a specific table.

regards,

Lars

[Former Member]

Thanks Lars and Neha for your responses , It cleared my doubts.

But if there is any document which helps to understand the merging mechanism clearly it would add more value to the existing documents.

Thanks Once again

Santosh

[Former Member]

Hi Santosh,

If you already load the data into SAP HANA and now you want to update the same table with data then only the change record will merge into the table. More simpler way you can say that merging the updated/delta record into the table.

Regards,

Neha

[Former Member]

Hi,

Excellent explanation provided by Lars :-).

Just to add, Delta merge is also automatically done by the system based on some thresholds settings.

The merge operations always trigger a re-write (of the table) in the main memory.

Regards, Rahul