microsoft/garnet · error · Exception

LatencyMonitor requires MetricsSamplingFrequency to be set

Error message

LatencyMonitor requires MetricsSamplingFrequency to be set

What it means

Latency tracking (LatencyMonitor) depends on the periodic metrics sampling task, which is driven by MetricsSamplingFrequency in seconds. If you enable latency monitoring but leave the sampling frequency at 0, the sampling task never runs, so the check at GetSettings refuses to start rather than silently producing no latency data.

Source

Thrown at libs/server/Servers/GarnetServerOptions.cs:755

                logger?.LogInformation("[Store] Hash index max size is optimized for up to ~{distinctKeys} distinct keys", PrettySize(AdjustedIndexMaxCacheLines * 4L));
            }
            logger?.LogInformation("[Store] Using log mutable percentage of {MutablePercent}%", MutablePercent);

            if (DeviceType == DeviceType.Default)
                DeviceType = Devices.GetDefaultDeviceType();
            DeviceFactoryCreator ??= new LocalStorageNamedDeviceFactoryCreator(
                deviceType: DeviceType,
                ioBackend: DeviceIoBackend,
                numCompletionThreads: DeviceCompletionThreads,
                throttleLimit: DeviceThrottleLimit > 0 ? DeviceThrottleLimit : null,
                logger: logger);
            if (DeviceType == DeviceType.Native && OperatingSystem.IsLinux())
                logger?.LogInformation("Using device type {deviceType} (io-backend={ioBackend}, completion-threads={ct}, throttle-limit={tl})", DeviceType, DeviceIoBackend, DeviceCompletionThreads, DeviceThrottleLimit > 0 ? DeviceThrottleLimit.ToString() : "device-default");
            else
                logger?.LogInformation("Using device type {deviceType} (throttle-limit={tl})", DeviceType, DeviceThrottleLimit > 0 ? DeviceThrottleLimit.ToString() : "device-default");

            if (LatencyMonitor && MetricsSamplingFrequency == 0)
                throw new Exception("LatencyMonitor requires MetricsSamplingFrequency to be set");

            // Read cache related settings
            if (EnableReadCache)
            {
                if (!EnableStorageTier)
                    throw new Exception("Read cache requires storage tiering to be enabled");
                kvSettings.ReadCacheEnabled = true;

                if (ReadCachePageCount != 0)
                    kvSettings.ReadCachePageCount = ReadCachePageCount;

                kvSettings.ReadCachePageSize = 1L << ReadCachePageSizeBits();
                kvSettings.ReadCacheMemorySize = ParseSize(ReadCacheMemorySize, out _);

                if (kvSettings.ReadCacheMemorySize > 0)
                {
                    var pageCount = kvSettings.ReadCacheMemorySize / kvSettings.ReadCachePageSize;
                    if (kvSettings.PageCount > pageCount)

View on GitHub (pinned to 951b0fc683)

Solutions

1. Set a positive --metrics-sampling-freq (seconds), e.g. --metrics-sampling-freq 1, alongside --latency-monitor.
2. If you do not actually need latency tracking, drop --latency-monitor.
3. Document the pairing in your deployment config so the two flags are always set together.

Example fix

# before (fails)
garnet-server --latency-monitor

# after
garnet-server --latency-monitor --metrics-sampling-freq 1

if (options.LatencyMonitor && options.MetricsSamplingFrequency == 0) {
    throw new InvalidOperationException("LatencyMonitor requires MetricsSamplingFrequency > 0");
}

When it happens

Trigger: Starting with --latency-monitor but with --metrics-sampling-freq unset or 0. Thrown at GarnetServerOptions.cs:754-755.

Common situations: Enabling latency monitoring in isolation without also turning on the metrics sampling cadence; assuming --latency-monitor self-schedules.

Related errors

• VectorSetReplayTaskCount should be in range [0,{Environment.
• VectorSetQuantizationTaskCount should be in range [0,{Enviro
• MutablePercent must be between 10 and 95
• Store Log Memory size or PageCount must be specified
• Index size {IndexMemorySize} should not be less than index m

AI-assisted analysis of microsoft/garnet@951b0fc683 (2026-08-13). Data as JSON: /api/errors/10247dadd0541c98. Report an issue: GitHub.