Full ERROR Message Example

Failed to register winmm.dll. Performance will be negatively impacted on this node.

What does this ERROR message mean?

On Windows systems, the multimedia timer services (winmm) allows an application to schedule periodic timer events — that is, the application can request and receive timer messages at application-specified intervals. Cassandra uses winmm.dll to control Windows kernel timer and scheduling resolution to a different value than its default of 15.6ms.

When the DLL is registered, the setting windows_timer_interval from cassandra.yaml can be tweaked, by lowering the default Windows value it is possible to achieve a much tighter latency and better throughput, however some virtualized environments may see a negative performance impact from changing this setting below their system default.

Why does this ERROR occur?

During Cassandra initialisation, in a Windows environment, Cassandra needs to register the Dynamic-link library winmm.dll. If this registration fails, a further error will be thrown advising that system timer on Windows was not tweaked from its default of 15ms.

How do you fix this ERROR?

Check the following possibilities:

1. Verify that winmm.dll exists in your Windows system
2. Confirm winmm.dll is located in C:\Windows\System32 folder.
3. Add the DLL path to system PATH variable.