Interview Questions On SAP HANA

• 1. Define Five-minute rule ?

It is a rule of thumb for deciding whether a data item should be kept in memory, or stored on disk and read back into memory when required. The rule is “randomly accessed disk pages of cache are re-used every 5 minutes”.

• 2. Define multi-core CPU ?

Multiple CPU’s on one chip or in one package is called multi-core CPU. 

• 3. Define Stall ?

Waiting for data to be loaded from main memory into the CPU cache is called as Stall.

• 4. What is SAP In-Memory Appliance (SAP HANA) ?

HANA is an in-memory technique to store data that is particularly suited for handling very large amounts of tabular, or relational, data with extra ordinary performance. Common databases store tabular data row-wise. Reorganizing the data in memory column-wise brings a tremendous speed increase when accessing a subset of the data in each table row.

• 5. What are the components or products of HANA ?

SAP HANA contains the following components.

 1. SAP HANA DATABASE

2. SAP HANA Studio SAP HANA CLIENT

3. SAP HANA INFORMATION COMPOSER

4. DIAGNOSTIC AGENT 7.3

5. SAP HANA client package for MS excel

6. SAP HANA UI for Information Access (INA)

7. SAP HANA AFL 1.0

8. Software Update Manager for SAP HANA

9. SAP LT Replication Add On

10. SAP LT Replication Server

11. SAP HANA Direct Extractor Connection (DXC)

12. SAP Data Services 4.0

• 6. What are the different editions available in HANA appliance software ?

Platform Edition:

Platform edition is intended for customers who want to use ETL-based replication and already have a license for SAP BO Data Services.

Enterprise Edition:

Enterprise edition is intended for customers who want to use either trigger-based replication or ETL-based replication and do not already have all of the necessary licenses for SAP BO Data Services.

• 7. What is columnar and Row-Based Data Storage ?

A database table contains data in the form of rows and columns. However Computer memory is organized as a linear structure. To store a table in linear memory, there are two options. A row-based storage stores a table as a sequence of records, each of which contains the fields of one row.  In a columnar storage the entries of a column are stored in contiguous memory locations. The SAP HANA database allows specifying whether a table is to be stored column-wise or row-wise. It is also possible to alter an existing table from columnar to row-based and vice versa. Search operations in tabular data can be accelerated by organizing data in columns instead in rows.

• 8. What are the advantages of Column based tables ?

The advantages of column based tables are: 

1. Calculations are typically executed on single or a few columns only.
2. The table is searched based on values of a few columns.
3. The table has a large number of columns.
4. The table has a large number of rows and columnar operations are required (aggregate, scan, etc.).
5. High compression rates can be achieved because the majority of the columns contain only few distinct values (compared to number of rows). 
• 9. What are the advantages of Row-based tables ?

The advantages of Row based tables are:

1. The application needs to only process a single record at one time (many selects and/or updates of single records).
2. The application typically needs to access a complete record (or row).
3. The columns contain mainly distinct values so that the compression rate would be low.
4. Neither aggregations nor fast searching are required.
5. The table has a small number of rows (e. g. configuration tables). 
• 10. Which case the data to be stored in columnar storage ?

To enable fast on-the-fly aggregations, ad-hoc reporting, and to benefit from compression mechanisms it is recommended that transaction data to be stored in a column-based table.

• 11. What is paralelization ?

Column-based storage makes it easy to execute operations in parallel using multiple processor cores. In a column store data is already vertically partitioned means that operations on different columns can easily be processed in parallel. If multiple columns need to be searched or aggregated, each of these operations can be assigned to a different processor core. In addition operations on one column can be parallelized by partitioning the column into multiple sections that can be processed by different processor cores

• 12. What are the different Compression Techniques ?

The compression techniques are:

1. Run-length encoding

2. Cluster encoding

3. Dictionary encoding

• 13. Why materialized aggregates are not required ?

With a scanning speed of several gigabytes per millisecond, in-memory column stores, make it possible to calculate aggregates on large amounts of data on the fly with high performance. This is expected to eliminate the need for materialized aggregates in many cases.

• 14. What are the advantages of Eliminating materialized aggregates ?

The advantages are:

1. Simplified data model
2. Simplified application logic
3. Higher level of concurrency and With the fly Aggregation we have aggregated values up to date
• 15. What are the different types of replication techniques ?

The replication techniques are:

1. ETL based replication using BODS

2. Trigger based replication using SLT

3. Extractor based data acquisition using DXC

• 16. Define SLT ?

SLT stands for SAP Landscape Transformation which is a trigger based replication. SLT replication server is the replication technology to pass data from source system to the target system. The source can be either SAP or non-SAP. Target system is SAP HANA system which contains HANA database.

• 17. What is Configuration in SLT ?

The information to create the connection between the source system, SLT system, and the SAP HANA system is specified within the SLT system as a Configuration. You can define a new configuration in Configuration & Monitoring Dashboard (transaction LTR).

• 18. What is Configuration and Monitoring Dashboard ?

It is an application that runs on SLT replication server to specify configuration information (such as source system, target system, and relevant connections) so that data can be replicated. It can also use it to monitor the replication status (transaction LTR).

Status Yellow: It may occur due to triggers which are not yet created successfully.

Status Red: It may occur if master job is aborted (manually in transaction SM37).

• 19. What is advanced replication settings ?

A transaction that runs on SLT replication server to specify advanced replication settings like

1. Modifying target table structures,
2. Specifying performance optimization settings
3. Define transformation rules

• 20. Define Latency ?

It is the length of time to replicate data (a table entry) from the source system to the target system.

• 21. Define logging table ?

A table in the source system that records any changes to a table that is being replicated. This ensures that SLT replication server can replicate these changes to the target system.

• 22. What are Transformation rules ?

A rule specified in the Advanced Replication settings transaction for source tables such that data is transformed during the replication process. Example you can specify rule to

1. Convert fields
2. Fill empty fields
3. Skip records
• 23. When to change the number of Data Transfer job ?

If the speed of the initial load/replication latency time is not satisfactory If SLT replication server has more resources than initially available, we can increase the number of data transfer and/or initial load jobs. After the completion of the initial load, we may want to reduce the number of initial load jobs.

• 24. What are the jobs involved in replication process ?

The replication process is consist following jobs:

1. Master Job (IUUC_MONITOR_)

2. Master Controlling Job (IUUC_REPLIC_CNTR_)

3. Data Load Job (DTL_MT_DATA_LOAD__<2digits>)

4. Migration Object Definition Job (IUUC_DEF_MIG_OBJ_<2digits>)

5. Access Plan Calculation Job (ACC_PLAN_CALC__<2digits>)

• 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).