SAP HANA: Interview Questions 11 through 20

11. What are Transformation rules?  
Transformation rule is a rule specified in the Advanced Replication settings transaction for source tables such a way that the data is transformed during the replication process.  

For example one can specify rule to Convert fields, Fill empty fields and Skip records.

12. When a new configuration is setup what happens?  
The database connection is automatically created along with GUID and Mass transfer id (MT_ID). 

Configurations with the same schema name can be created which is ensured by schema GUID. 

The naming of SLT jobs and the system can uniquely identify a schema where the Mass transfer ID is used. 
  

13. What are the factors that influence the change/increase in the number of jobs? 
 The factors that influence the change or increase in the number of jobs are number of configurations managed by the SLT replication server, number of tables to be loaded/ replicated for each configuration, expected speed of initial load, expected replication latency time.  

As a thumb rule, one BDG job should be used for each 10 tables in replication to achieve acceptable latency times.  

14. When is the number of Data Transfer jobs changed?  
The number of data Transfer jobs changes when the speed of the initial load/replication latency time is not satisfactory, if SLT replication server has more resources than that is initially available.  

The number of initial load jobs may be reduced after the completion of the initial load. 

15. Mention the jobs involved in replication process?  
The main jobs involved in the replication process are stated as below: 

• Master Job (IUUC_MONITOR_<MT_ID>) 

• Master Controlling Job (IUUC_REPLIC_CNTR_<MT_ID>) 

• Data Load Job (DTL_MT_DATA_LOAD_<MT_ID>_<XX>) 

• Migration Object Definition Job (IUUC_DEF_MIG_OBJ_<XX>) 

• Access Plan Calculation Job (ACC_PLAN_CALC_<MT_ID>_<XX>)  

16. State the relation between the number of data transfer jobs in the configuration settings and the available BGD work processes? 
 In SLT replication server each job occupies 1 BGD work processes and for each configuration, the parameter Data Transfer Jobs would restrict the maximum number of data load job for each mass transfer ID (MT_ID). 

At least 4 background jobs are required for a mass transfer ID requires to be available.  

They are One master job, One master controller job, At least one data load job, One additional job either for migration/access plan calculation/to change configuration settings in “Configuration and Monitoring Dashboard”. 

17. If the parameter set for “data transfer jobs” to 04 in a configuration “SCHEMA1”, a mass transfer ID 001 is assigned. In such a case what jobs should be in the system?  
The jobs should be 1 Master job (IUUC_MONITOR_SCHEMA1), 1 Master Controller job (IUUC_REPL_CNTR_001_0001) and at most 4 parallel jobs for MT_ID 001 (DTL_MT_DATA_LOAD_001_ 01/~02/~03/~04). 

If at the same time lots of tables are selected for load / replication, there could be a chance that there are not enough background jobs available to start the load procedure for all tables immediately.  

In such a case the number of initial load jobs can be increased, or else tables will be handled sequentially. 

For tables with large volume of data the transaction “Advanced Replication Settings (IUUC_REPL_CONT)” to further optimize the load and replication procedure for dedicated tables can be used. 
  

18. After the SLT replication is over what happens?
 After the replication is over, the SLT replication server creates 1 user, 4 roles, 2 stored procedures, and 8 tables: 

• 1 User 

• 1 Privilege 

• 4 Roles 

• <REPLICATION SCHEMA>_DATA_PROV 

• <REPLICATION_SCHEMA>_POWER_USER 

• <REPLICATION_SCHEMA>_USER_ADMIN 

• <REPLICATION_SCHEMA>_SELECT 

• 2 Stored procedures 

• RS_GRANT_ACCESS, RS_REVOKE_ACCESS 

• 8 Tables 

• DD02L, DD02T, RS_LOG_FILES, RS_MESSAGES, RS_ORDER, RS_ORDER_EXT, RS_SCHEMA_MAP, RS_STATUS 

19. State the different replication scenarios?  
The different replication scenarios are Load, Replicate, Stop, Suspend and Resume. 

Before any application table is selected, the initial load of the tables DD02L, DD02T & DD08L must be completed as they contain the metadata information. 

Load: This starts an initial load of replication data from the source system.  

The complete procedure is a one-time event.  

Once completed, further changes to the source system database will not be replicated.  

Also for the initial load procedure, neither database triggers nor logging tables are created in the source system.  

The 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.  

Replicate: This combines an initial load procedure and the subsequent replication procedure (real time or scheduled). 

Before the start of initial load procedure, trigger of database and related logging table are created for each table in the source system as well as in SLT replication server.  

Stop Replication: This stops any current load or replication process of a table. 

The stop function removes the database trigger and related logging tables completely.  

This function is used only if you want to continue a selected table otherwise it must be initially loaded again to ensure data consistency.  

Suspend: This pauses a table from a running replication.  

Also the database trigger will not be deleted from the source system.  

The recording of changes would continue and the related information would be stored in the related logging tables in the source system. 

If tables are suspended for a long time the size of logging tables may increase and adjust the table space if required.  

Resume: This restarts the application for a suspended table.  

The previous suspended replication will be resumed (no new initial load required).
   

20. If the replication is suspended for a long period of time or system outage of SLT or HANA system what would happen?  
The size of the logging tables would increase.