[BUG] Combining Jitter and FailSafeThrottleDuration leads to wrong or at least unexpected behavior

[fabianmenges]

Describe the bug

I'm using a 2 level cache, MemoryCache + Redis with the FailSafe option enabled.

• I don't want my DefaultFailSafe value to be cached at all - which means i need to set the FailSafeThrottleDuration to TimeSpan.Zero.
• I still want to add jitter for the caching duration of non-default values.
  It seems like jitter is also applied to to the FailSafeThrottleDuration - which is unexpected and in my case undesired behavior.

To Reproduce

In my opinion this should not throw an exception (but it does):

    public async ValueTask Test() {
        var expectedNegOne = await _cache.GetOrSetAsync<int>("111derp",
            (ctx, ct) => Task.FromResult(ctx.Fail("test")),
            failSafeDefaultValue: -1,
            options => options
                .SetDuration(TimeSpan.FromMinutes(value: 180))
                .SetJittering(TimeSpan.FromMinutes(value: 30))
                .SetFailSafe(isEnabled: true, throttleDuration: TimeSpan.Zero)
        );
        await Task.Delay(TimeSpan.FromSeconds(value: 5));
        var expectedOne = await _cache.GetOrSetAsync<int>("111derp",
            (ctx, ct) => Task.FromResult(ctx.Modified(value: 1)),
            failSafeDefaultValue: -1,
            options => options
                .SetDuration(TimeSpan.FromMinutes(value: 180))
                .SetJittering(TimeSpan.FromMinutes(value: 30))
                .SetFailSafe(isEnabled: true, throttleDuration: TimeSpan.Zero)
        );

        if (expectedNegOne != -1) {
            throw new Exception("Expected -1");
        }
        if (expectedOne != 1) {
            throw new Exception("Expected 1");
        }
    }

Expected behavior

I would have expected the code above to perform identically to this code:

    public async ValueTask Test() {
        var expectedNegOne = await _cache.GetOrSetAsync<int>("111derp",
            (ctx, ct) => Task.FromResult(ctx.Fail("test")),
            failSafeDefaultValue: -1,
            options => options
                .SetDuration(TimeSpan.FromMinutes(value: 180))
                .SetFailSafe(isEnabled: true, throttleDuration: TimeSpan.Zero)
        );
        await Task.Delay(TimeSpan.FromSeconds(value: 5));
        var expectedOne = await _cache.GetOrSetAsync<int>("111derp",
            (ctx, ct) => Task.FromResult(ctx.Modified(value: 1)),
            failSafeDefaultValue: -1,
            options => options
                .SetDuration(TimeSpan.FromMinutes(value: 180))
                .SetFailSafe(isEnabled: true, throttleDuration: TimeSpan.Zero)
        );

        if (expectedNegOne != -1) {
            throw new Exception("Expected -1");
        }
        if (expectedOne != 1) {
            throw new Exception("Expected 1");
        }
    }

Versions

I've encountered this issue on:

• FusionCache version 1.4.1
• .NET version net8.0
• OS version Ubuntu 24.04.1 LTS (Noble Numbat)
• Using Redis (should not play a role - I have not tested it without redis)

[jodydonetti]

Hi @fabianmenges , I think you're right: jittering should not be considered when doing fail-safe throttling.

I'll think about it a bit more and, if nothing comes up, I'll do the change.

Will update you, meanwhile thanks for bringing this up!