HOST: Measuring Network Latency

Operating SystemPerformanceWindows

Symptoms: Network traffic slowing – user responses are slow and some data may be lost.

Impact: Medium

Slow SQL responses will degrade the user experience, resulting in poor efficiency of your organization’s operations. Specifically, network latency can also lead to data loss and corruption as well as network jitter.

Expected behavior :

There is no standard metric for network latency. Many aspects of the environment will affect network latency.

Reliable connections consistently report back the same network latency over and over again. Using AimBetter’s algorithm, the alert displays when average network latency deviates more than the threshold level permitted.

Possible causes of network latency

High network traffic – system   Priority: Medium
Unusual levels of network load may be coming from external operations moving data around the network (backups, restores, etc from networked data stores)
Recommended action :
Identify the source of the load (using built-in OS tools such as PerfMon) and if it is recurrent, try to reschedule to a time of low user demand. Where possible, concentrate non-SQL Server related activities onto a separate network. Also, schedule high-volume activities to time frames of lowest user demand.

SQL queries with high disk I/O requiring data traffic to storage  Priority: Medium
This problem is specifically relevant to environments with networked storage.
Recommended action :
If possible, log storage disks should be physically linked to the server, or over a separate network. To otherwise minimize traffic, see our recommendations regarding page file optimization here.

Network errors or inefficient network structure  Priority: Medium

Recommended action :
Investigate all hardware components, with your Network Management team.
See our recommendations regarding network levels here.


This alert means that network traffic is taking longer times to complete. The alert displays when average network latency exceeds the threshold you have set. Network latency depends on the speed of the transmission and is affected by the delays in the transmission by devices along the way (e.g., routers and modems). Low latency indicates high network efficiency. Network latency has a strong correlation with network jitter. If traffic has to move over a shared network using remote storage, it could cause substantial increases in traffic, resulting in network latency causing jitter.

In the case of data storage on networked devices, it is necessary to take the following into account: SQL Server typically has a high demand for disk I/O activity. If insufficient data resides in a buffer pool cache to satisfy queries, the system has to pull data from disk. Further, since the data in databases is constantly changing these updates need to be written to disk. Another process that can consume a lot of I/O is the TempDB database which is a temporary working area for SQL Server to organize data drawn from tables. This database also resides on disk and could be changing and growing. If this traffic has to move over a shared network using remote storage, it could cause substantial increases in traffic, resulting in network latency which could lead to jitter.

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