Reconfiguring a Scale-Out SAP HANA System

Business Example

As an SAP HANA database administrator, you must be able to reconfigure your company’s high availability scale-out SAP HANA systems. You require hands-on experience with reconfiguring multi-host SAP HANA systems.

Reconfigure a Scale-out SAP HANA System

The SAP HANA database supports high availability in a distributed system by providing for host auto-failover. If an active host fails, for example, because of a hardware failure, standby hosts can take over and ensure the continued availability of the database.

In SAP HANA cockpit 2.0, you can monitor the status of individual hosts in the Host Failover application. To start the Host Failover application, open SAP HANA cockpit 2.0 and navigate to the Aggregate Health Monitor application. In the Aggregate Health Monitor, select the SYSTEMDB@<SID> link to open the SAP HANA Cockpit Overview screen.

On the SAP HANA Cockpit Overview screen, search for the Configure Host Failover application, and select the Configure host failover link. The same application is also available from the tenant database, <SID>@<SID>, but this task is normally something you perform from SYSTEMDB.

The Configure Host Failover app shows the configured state in the configured role columns. The Actual Role column shows the current state. Use the settings button to add or remove columns.

Host roles for failover are normally configured during installation. Using the SAP HANA cockpit, you can monitor the status of individual hosts and switch the configured roles of hosts. You cannot increase or decrease the number of worker hosts and standby hosts with respect to each other.

The primary reason for changing the configured roles is to prepare for the removal of a host. In this case, change the configured role of the name server host to WORKER and the configured role of the index server host to STANDBY before stopping the database instance on the host and removing the host.

The reconfiguration is done by setting the master parameter in the landscape section of the nameserver.ini file.

With the following SQL command, you specify which three hosts are coordinator candidates:

Code Snippet

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ALTER SYSTEM ALTER CONFIGURATION ( 'nameserver.ini' , 'SYSTEM' ) 
  SET ('landscape', 'master') = 'wdflbmt7346:30001 wdflbmt7347:30001 wdflbmt7348:30001' WITH RECONFIGURE;

With the following SQL command, you specify which host is the coordinator :

Code Snippet

12
ALTER SYSTEM ALTER CONFIGURATION ( 'nameserver.ini' , 'SYSTEM' ) 
  SET ('landscape', 'active_master') = 'wdflbmt7347:30001' WITH RECONFIGURE;

In the SAP HANA Cockpit - Host Failover, you can add or remove columns in the display by choosing the gear button in the top-right corner. When adding or removing hosts from a multi-host SAP HANA system, the remove status column indicates the status of the table redistribution operation used to move data off the index server of a host that you plan to remove.

Before you can remove an active host from a single-container system, you must move the tables on the index server of this host to the index servers on the remaining hosts in the system. Once the value in the removal status column changes to REORG FINISHED or REORG NOT REQUIRED, you can physically remove the host using the SAP HANA lifecycle management tool, hdblcm(gui).

If your system is configured as a multiple-container system, you must remove tenant-specific services first and then remove the host using the SAP HANA database lifecycle manager.

Steps to Remove indexserver

call SYS.UPDATE_LANDSCAPE_CONFIGURATION('SET REMOVE','<hostname:port>');
call REORG_GENERATE(2,'NO_SPLIT’);
call REORG_EXECUTE(?);
select * from SYS.REORG_OVERVIEW order by REORG_ID DESC;

Host Removal Status

Status	Removal possible
Reorg pending	No
Reorg active	No
Reorg failed	No
Reorg finished	Yes
Reorg not required	Yes

The following statuses are possible:

<Empty>: The host has not been marked for removal.
REORG PENDING: A redistribution operation is required to move tables to other hosts.
REORG ACTIVE: A redistribution operation is in progress. For more information, you can query the system tables SYS.REORG_OVERVIEW and SYS.REORG_STEPS.
REORG FAILED: A redistribution operation was executed and failed. For more information, query the system table SYS.REORG_STEPS.
REORG FINISHED: A redistribution operation has completed. The host can be uninstalled.
REORG NOT REQUIRED: A redistribution operation is not required. The host can be uninstalled.

The assignment rules for scale-out coordinators.

During the SAP HANA installation of a multi-host system, the optimal auto-failover configuration is set up.

The optimal configuration is described in the following setup:

coordinator 1: Assigned to the node where the installation is performed.
coordinator 2: Assigned to the first additional node that is assigned to the multi-host system.
coordinator 3: Assigned to the first standby node assigned to the multi-host system. If there is no standby host configured, the second additional node that is assigned to the multi-host system is used. A setup without at least one standby node will not be a useful high-availability scenario.

Host Auto-failover Required Authorizations

Required authorizations to change host configuration

System privilege RESOURCE ADMIN
Object privilege EXECUTE on the procedure UPDATE_LANDSCAPE_CONFIGURATION

Additional Information

Additional Information	SAP Note
FAQ: SAP HANA High Availability	2057595
How-To Guides & Whitepapers For SAP HANA High Availability	2407186
HANA: How to remove the master host in a Multi-host system	2144720