Soenneker.Deduplication.Redis 4.0.87

Soenneker.Deduplication.Redis

Distributed, time-bounded duplicate suppression using atomic Redis markers.

Installation

dotnet add package Soenneker.Deduplication.Redis

Registration

using Soenneker.Deduplication.Redis.Registrars;

services.AddRedisDedupeAsSingleton();

This also registers Soenneker.Redis.Client; configure its Redis connection using that package’s normal configuration.

Usage

using Soenneker.Deduplication.Redis.Abstract;

public sealed class WebhookConsumer(IRedisDedupe dedupe)
{
    public async ValueTask Handle(string eventId, CancellationToken cancellationToken)
    {
        bool firstDelivery = await dedupe.TryMarkSeen(
            cacheKey: "dedupe:webhooks:stripe",
            cacheValue: eventId,
            expiration: TimeSpan.FromHours(24),
            cancellationToken);

        if (!firstDelivery)
            return;

        await ProcessWebhook(cancellationToken);
    }
}

TryMarkSeen uses Redis SET ... NX with the TTL in the same command. Concurrent callers across processes get one true result while the marker exists; later callers get false. Redis connection and command failures propagate instead of being reported as duplicates.

Lookup and removal

bool seen = await dedupe.Contains("dedupe:webhooks:stripe", eventId, cancellationToken);
bool removed = await dedupe.TryRemove("dedupe:webhooks:stripe", eventId, cancellationToken);

Contains does not refresh the TTL. TryRemove performs one atomic Redis delete and returns whether a marker was deleted.

String and ReadOnlySpan<char> overloads hash UTF-16 characters. TryMarkSeenUtf8, ContainsUtf8, and TryRemoveUtf8 hash the supplied bytes. Use the same representation for every operation on a value; the UTF-16 string "abc" and its UTF-8 bytes are different dedupe keys.

Redis keys and retention

The stored key is:

{cacheKey}:{lowercase 16-character XXH3-64 hash}

Only the 64-bit hash marker is stored as the value, but cacheKey remains visible in Redis. Choose a stable, non-secret namespace. Different inputs can theoretically collide, so use a full-key design when collision tolerance is unacceptable.

Always set an expiration for open-ended inputs unless permanent markers and their storage growth are intentional. A non-positive expiration is rejected; null creates a marker without automatic expiry.

Delivery semantics

This package is a duplicate-suppression primitive, not an exactly-once transaction. The marker and your business operation are separate: a process can fail after claiming a value but before completing the work. For durable message processing, combine it with an inbox/outbox or another transactional idempotency design. Redis eviction, data loss, manual deletion, or TTL expiry can also make a value eligible again.