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logreplay Operation Mode for HANA System Replication

17 Aug 2017 9:46 am || 0

The following table compares the original operation mode delta_datashipping with the operation mode logreplay available as of SAP HANA >= SPS 11:

Operation mode SAP HANA Version Description Advantages
delta_datashipping no restriction Synchronization between primary and secondary site is implemented via regular delta data shippings from primary to secondary site.
  • Memory footprint of secondary site can be smaller as column store tables don't have to be loaded during system replication
  • As a consequence it is possible to set the global_allocation_limit (SAP doc 1999997) and run an additional non-production system on the same machine.
  • History tables are generally supported (for logreplay modes the restrictions described in SAP doc 2480889 apply)
logreplay >= 1.00.110 Synchronization between primary and secondary site is implemented purely based on redo logs
  • Delta data shipping no longer required
  • Reduced network traffic between primary and secondary site
  • Reduced network bandwidth requirements between primary and secondary site
  • Reduced takeover times (shorter log replay, no persistence garbage collection, no file ID mapping and disk LOB initialization, no adjustment of resource container dispositions; see SAP doc 2222217)
  • No propagation of logical persistence corruptions on disk level (e.g. introduced by the bug described in SAP doc 2375691)
logreplay_readaccess >= 2.00

Synchronization between primary and secondary site is implemented purely based on redo logs

Secondary site can be used for read-only accesses (on column store tables)

  • Same advantages like "logreplay" above
  • Query load can be moved away from primary site

The operation mode can be defined with the following parameter:

global.ini -> [system_replication] -> operation_mode

In 3-tier environments the following details can be considered for the logreplay mode:

  • If the tertiary system is down, the logs are only saved on the secondary system, not on the primary system.
  • If the secondary system is down and you want to use the tertiary system as secondary system, usually a full sync is required, because the logs retained on primary site are meant for the secondary site and so they may not be compatible with the tertiary system.