During COMMITs the changes of the transaction are persisted to disk and made visible for other transactions.
Factors can influence the time of COMMIT operations such as Disk I/O write performance to logs, Synchronous system replication mode, Synchronous table replication, High amount of active versions, Integrated liveCache and SAP HANA bugs.
|Disk I/O write performance to logs||During COMMITs the change information is written to the log files. If writing down the data is slow, the COMMIT times can increase.|
|Synchronous system replication mode||If a synchronous system replication mode is activated, changes are propagated to the replication side during a COMMIT, and the local session has to wait for an acknowledgement. If you suffer from long COMMIT times in a system with activated synchronous system replication, you should at first check if a switch to a less critical system replication mode (e.g. SYNC -> SYNCMEM or SYNCMEM -> ASYNC) improve the performance. If yes, you can analyze if there are unnecessary replication delays, e.g. due to limited network bandwidth or high latency times.|
|Synchronous table replication|| |
If a transaction performs changes on a table with activated optimistic synchronous table replication (OSTR), the replicas need to be refreshed during COMMIT. This can have an adverse impact on the COMMIT performance.
|High amount of active versions||The COMMIT performance can be significantly impacted by a high amount of active versions.|
|Integrated liveCache|| |
If a SAP HANA integrated liveCache is used, the SAP HANA COMMIT performance can be impacted by related COMMITs on liveCache side.
The time for the 'Kernel-Commit' method is part of the SAP HANA COMMIT time. Other related times like 'Flush-Cache', 'Commit-Invalidate-Callback' and 'Validate-Callback' have to be considered on top of the SAP HANA COMMIT time.
During a liveCache COMMIT a potentially large amount of data has to be flushed, so in case of high COMMIT times you should always consider the amount of flushed data to judge if it is more an I/O issue or a data volume issue.
|SAP HANA bugs|| |
The following SAP HANA bugs can be responsible for increased COMMIT times:
If COMMITs take very long, a termination with error "snapshot timestamp synchronization failed" is possible.