Thursday, 5 February 2015

Technical Round SAP HANA Interview Questions and Answers (Part3)

Below are some important SAP HANA interview questions which are asked in most MNC company interviews for beginners or professionals.
21. What are the different replication scenarios?
Different replication scenarios are:
Load, Replicate, Stop, Suspend and Resume.

Starts an initial load of replication data from the source system. The procedure is a one-time event. After it is completed, further changes to the source system database will not be replicated.
 For the initial load procedure, neither database triggers nor logging tables are created in the source system. Default settings use reading type 3 (DB_SETGET) with up to 3 background jobs in parallel to load tables in parallel or subsequently into the HANA system.

Combines an initial load procedure and the subsequent replication procedure (real time or scheduled).
 Before the initial load procedure will start, database trigger and related logging table are created for each table in the source system as well as in SLT replication server.

Stops any current load or replication process of a table.
 The stop function will remove the database trigger and related logging tables completely. Only use this function if you do want to continue a selected table otherwise you must initially load the table again to ensure data consistency.

Pauses a table from a running replication. The database trigger will not be deleted from the source system. The recording of changes will continue and related information is stored in the related logging tables in the source system.
 If you suspend tables for a long time the size of logging tables may increase and adjust the table space if required.

Restarts the application for a suspended table. The previous suspended replication will be resumed (no new initial load required).

22. What happens if the replication is suspended for a long period of time or system outage of SLT or HANA system?
The size of the logging tables increases.

23. How to avoid unnecessary logging information from being stored?
Pause the replication by stopping the schema-related jobs.

24. Will the table size in SAP HANA database and in the source system the same?
No. As HANA database supports compression, the table size in SAP HANA may be decreased.

25. When to go for table partitioning?
If the table size in HANA database exceeds 2 billion records, split the table by using portioning features by using “Advanced replication settings” (transaction IUUC_REPL_CONT, tab page IUUC_REPL_TABSTG).

26. Where do you define transformation rules?
By using “Advanced replication settings” (transaction IUUC_REPL_CONT, tab page IUUC ASS RULE MAP)

27. Are there any special considerations if the source system is non-SAP system?
The concept of trigger-based replication is actually meant for SAP source systems. The main differences are:
There will be a database connection between non-SAP source and SLT system instead of RFC.
Source must have primary key
Tables DD02L,  DD02T which contains metadata are just initially loaded but not replicated.
The read modules reside on SLT system.
Tables with database specific formats may need transformation rules before they are replicated.
Only SAP supported databases  are supported as non-SAP source systems.

28. Does SLT for SAP HANA support data compression like SAP HANA database?
Yes, this is automatically covered by the RFC connection used for data replication from the SAP source system.

29. Will the table size in SAP HANA database and in the source system the same?
No as HANA database supports compression.

30. How can you ensure that data is consistent in source system and HANA system?
Since any changes in the source system is tracked in dedicated logging tables, the replication status for each changed data record is transparent. A entry of logging table is deleted after a successful commit statement from HANA database and this procedure ensures the data consistency between source system and HANA system.
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