Introduction
In the upcoming weeks, we will be posting new videos to the
SAP HANA Academy to show new features and functionality introduced with
SAP HANA 2.0 Support Package Stack (SPS) 03.
The topic of this blog is
high availability.
For the previous versions of this blog, see
For the full SAP HANA 2.0 SPS 03 blog list, see
What's New?
SAP HANA System Replication Playlist
On the SAP HANA Academy, there is a
full playlist covering all aspects of system replication:
SAP HANA Academy - SAP HANA System Replication playlist
SAP HANA System Replication
Multitarget System Replication
As of SPS 03, the primary system can now replicate data changes to more than one secondary system. Different disaster recovery scenarios apply, depending on whether just the primary or the whole data center experiences a failure.
For the documentation, see
Invisible Takeover
In a regular takeover scenario, all connections to the clients on the primary system are lost and there is no awareness of any previous client connection on the secondary host.
SPS 03 introduces invisible takeovers, which enables the client to keep the connections to the primary system and to restore its sessions on the secondary system. However, only read transactions are supported. When the ongoing transaction is a write transaction, the session won't be recovered.
his is configured through the use of the enable_session_recovery parameter.
For the documentation, see
Secondary Time Travel
It is now possible to start the secondary system in online mode on a previous point in time. Secondary time travel can be used to quickly access again data, which was deleted in the original system.
Time travel on the secondary host is only possible in the operation modes logreplay or logreplay_readaccess.
The retention time is set with the timetravel_max_retention_time parameter in global.ini, section system_replication. For time travel to work, log and snapshots are kept online in the data area and you need to set the parameter carefully to avoid log full or disk full situations.
hdbnsutil -sr_timetravel --startTime=<startTime>
[--callTakeoverHooks=on|off].
For the documentation, see
Alert 106 - ASYNC replication in-memory buffer overflow
Alert 106 is raised when the local in-memory buffer in the ASYNC replication mode is running full indicating possible network issues with the connection to the secondary system.
For the documentation, see
Host Auto-Failover Parameters
Host Auto-Failover is a built-in, fully automated high availability solution for recovering from the failure of an SAP HANA host, introduced in SAP HANA 1.0 SPS 09.
SPS 03 adds two new parameters for host auto-failover.
- enable_master_failover - defaults to true; when set to false the check of the nameserver master candidates is disabled
- startup_error_restart_retries - defaults to 4; defines the number of retries if a service fails in the startup procedure
For the documentation, see
getTakeoverRecommendation.py
The
getTakeoverRecommendation.py Python script evaluates the status of the primary system and of the system replication to help decide if a takeover is justified.
For the documentation, see
References
SAP HANA Documentation
SAP Notes
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