## 8.5.4  Monitoring the Network Latency
You can monitor the network latency with the SAP HANA cockpit or the SAP HANA studio.
The latency for the redo log shipping is of interest in a running system replication for the synchronous replication modes SYNC or SYNCMEM regardless of the used operation mode.
##  Note
The redo log shipping wait time for 4 KB log buffers must be less than a millisecond or in a low single-digit millisecond range - depending on the application requirements (relevant for synchronous replication modes only).
All changes to data are captured in the redo log. The SAP HANA database asynchronously persists the redo log with I/O orders of 4 KB to 1 MB size into log segment files in the log volume of the primary system. A transaction writing a commit into the redo log waits until the buffer containing the commit has been written to the log volume. This wait time for 4 KB log buffers should be less than a millisecond or in a low single-digit millisecond range. Once you configured system replication, you can check the local and the remote log write wait times in the SAP HANA cockpit or collect them in the SAP HANA studio with the SQL statement HANA\_Replication\_Overview attached to the SAP Note 1969700 .
## Network Latency in the SAP HANA Cockpit
In the SAP HANA cockpit you receive an overview of your running system replication displaying the average log buffer size between the primary and the secondary, as well as the average redo log shipping wait time. Opening the Network tab, you can also have a look at the 24 hour history of these local log write wait times and the remote log shipping wait times. For more information, see Example: Monitoring SAP HANA System Replication with the SAP HANA Cockpit .
For example:
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## Network Latency in the SAP HANA Studio
You can gather these values also with the SAP HANA studio after importing the SQL statement collection (attached to SAP Note 1969700 ) to the SAP HANA studio: System Information Import SQL Statements .
Right-click on the statements under Replication Overview and choose Execute from the context menu. You will receive information about the system replication landscape and the replication state for each service.
The log write wait times on the 'local' system (that is, on the persistence of the primary system) is returned by the mentioned SQL statement as Average local log buffer write time (ms) per service, where the index server is the one of interest.
Additionally, the mentioned SQL statement returns the redo log write latency for the shipping to the secondary, which can be slightly higher than the locally measured log write wait time. The returned value Average local log buffer write time (ms) represents the time between enqueueing and finishing a request.
Of interest is also the Local log buffer write throughput (MB/s) compared to the Log buffer shipping throughput (MB/s) in synchronous replication. If these two values differ too much, this could be an indication for network problems in a synchronous replication or a problem with the I/O on the secondary system (for SYNC). For information about ASYNC replication, see the Check Network Configuration (Long Distance) section in Replication Performance Problems .
## Related Information
Example: Monitoring SAP HANA System Replication with the SAP HANA Cockpit [page 177]
Replication Performance Problems [page 216]
SAP Note 1969700