microsoft/garnet · error · TsavoriteException

LogSettings.LogDevice needs to be specified (e.g., use Devic

Error message

LogSettings.LogDevice needs to be specified (e.g., use Devices.CreateLogDevice, AzureStorageDevice, or NullDevice)

What it means

Constructor validation: logSettings.LogDevice must be non-null. The allocator persists and recovers via this IDevice; without one there is nowhere to read/write the log. The message suggests concrete factories: Devices.CreateLogDevice, AzureStorageDevice, or NullDevice (the last for in-memory-only / ephemeral use).

Source

Thrown at libs/storage/Tsavorite/cs/src/core/Allocator/AllocatorBase.cs:587

                    throw new TsavoriteException($"{nameof(rcs.PageSizeBits)} must be between {LogSettings.kMinPageSizeBits} and {LogSettings.kMaxPageSizeBits}");
                if (rcs.PageCount > MemoryUtils.ArrayMaxLength)
                    throw new TsavoriteException($"{nameof(rcs.PageCount)} must be less than or equal to the maximum array length ({MemoryUtils.ArrayMaxLength})");
                if (rcs.MemorySize != 0 && (rcs.MemorySize < 1L << LogSettings.kMinMemorySizeBits || rcs.MemorySize > 1L << LogSettings.kMaxMemorySizeBits))
                    throw new TsavoriteException($"{nameof(rcs.MemorySize)} must be between {1L << LogSettings.kMinMemorySizeBits} and {1L << LogSettings.kMaxMemorySizeBits}");
                if ((rcs.MemorySize != 0) && (rcs.MemorySize < (1L << rcs.PageSizeBits) * 2))
                    throw new TsavoriteException($"{nameof(logSettings.MemorySize)} must be at least twice the page size ({1L << rcs.PageSizeBits})");
                if (rcs.SecondChanceFraction < 0.0 || rcs.SecondChanceFraction > 1.0)
                    throw new TsavoriteException($"{rcs.SecondChanceFraction} must be >= 0.0 and <= 1.0");
            }

            if (logSettings.MaxInlineKeySize < LogSettings.MinMaxInlineSize || logSettings.MaxInlineKeySize > LogSettings.MaxInlineKeySizeLimit)
                throw new TsavoriteException($"{nameof(logSettings.MaxInlineKeySize)} must be between {LogSettings.MinMaxInlineSize} and {LogSettings.MaxInlineKeySizeLimit}");
            if (logSettings.MaxInlineValueSize < LogSettings.MinMaxInlineSize || logSettings.MaxInlineValueSize > LogSettings.MaxInlineValueSizeLimit)
                throw new TsavoriteException($"{nameof(logSettings.MaxInlineValueSize)} must be between {LogSettings.MinMaxInlineSize} and {LogSettings.MaxInlineValueSizeLimit}");

            this.logger = logger;
            if (logSettings.LogDevice == null)
                throw new TsavoriteException("LogSettings.LogDevice needs to be specified (e.g., use Devices.CreateLogDevice, AzureStorageDevice, or NullDevice)");

            EvictCallback = evictCallback;

            FlushCallback = flushCallback;
            PreallocateLog = logSettings.PreallocateLog;
            flushEvent.Initialize();

            IsNullDevice = logSettings.LogDevice is NullDevice;

            if (epoch == null)
            {
                this.epoch = new LightEpoch();
                isEpochOwned = true;
            }
            else
                this.epoch = epoch;

            logSettings.LogDevice.Initialize(1L << logSettings.SegmentSizeBits, epoch);

View on GitHub (pinned to 951b0fc683)

Solutions

Assign a real device: `LogDevice = Devices.CreateLogDevice(path)`.
For ephemeral/in-memory stores use `LogDevice = new NullDevice()`.
For Azure-backed storage use AzureStorageDevice as the message suggests.

Example fix

// before
var s = new LogSettings { PageSizeBits = 25 /* LogDevice never set */ };
// after
var s = new LogSettings { LogDevice = Devices.CreateLogDevice("./data"), PageSizeBits = 25 };
// or, in-memory only
var s = new LogSettings { LogDevice = new NullDevice() };

Defensive patterns

Strategy: type-guard

Validate before calling

if (logSettings.LogDevice is null)
    throw new ArgumentException("LogSettings.LogDevice is null. Use Devices.CreateLogDevice(path), AzureStorageDevice, or new NullDevice().");

Type guard

static bool HasLogDevice(LogSettings s) => s?.LogDevice is not null;

// usage
if (!HasLogDevice(logSettings)) logSettings.LogDevice = Devices.CreateLogDevice(DefaultPath);

Try / catch

try { new TsavoriteKV<K,V>(logSettings, ...); }
catch (TsavoriteException ex) when (ex.Message.Contains("LogDevice needs to be specified"))
{ /* assign logSettings.LogDevice (CreateLogDevice/AzureStorageDevice/NullDevice) and recreate */ }

Prevention

Always assign LogDevice in the same object initializer that builds LogSettings.
Use NullDevice explicitly for in-memory tests rather than relying on a null default.
Centralize device creation in one factory so LogDevice is never left null.

When it happens

Trigger: Constructing TsavoriteKV/TsavoriteLog with `LogSettings.LogDevice = null` (e.g. forgetting to assign it, or a factory call that returned null on a bad path).

Common situations: Building LogSettings from a config object whose LogDevice field was never populated; conditional device creation where the branch returned null; tests that intended NullDevice but assigned nothing.

Related errors

AI-assisted analysis of microsoft/garnet@951b0fc683 (2026-08-13). Data as JSON: /api/errors/cb70681615e6a354. Report an issue: GitHub.