[BUG] RemoveByTagAsync does not work when SkipMemoryCacheWrite = true

[sebbarg]

Describe the bug

When setting SkipMemoryCacheWrite = true (and optionally also SkipMemoryCacheRead = true), RemoveByTagAsync does not remove tagged entries from level 2 cache.

To Reproduce

    [Test, Explicit]
    public async Task ItShould()
    {
        const bool bypassMemory = true;

        var services = new ServiceCollection();

        services.AddLogging(logging =>
        {
            logging.AddConsole();
            logging.SetMinimumLevel(LogLevel.Debug);
        });

        services.AddFusionCache()
            .WithSerializer(
                new FusionCacheSystemTextJsonSerializer()
            )
            .WithDistributedCache(
                new RedisCache(new RedisCacheOptions { Configuration = _redisContainer!.GetConnectionString() })
            );

        var serviceProvider = services.BuildServiceProvider();

        var cache = serviceProvider.GetRequiredService<IFusionCache>();
        var tags = new[] { "foo" };

        var id = Guid.NewGuid();
        var key = $"TheKey:{id}";
        var value = await GetProductFromDbAsync(id); // This is just a simulation that creates a simple POCO

        // Create cache entry with tags
        await cache.SetAsync(key, value,
            setupAction =>
            {
                setupAction.SkipMemoryCacheRead = bypassMemory;
                setupAction.SkipMemoryCacheWrite = bypassMemory;
            },
            tags);

        // Ensure it's retrievable
        var record2 = await cache.GetOrDefaultAsync<PocoA?>(key,
            setupAction =>
            {
                setupAction.SkipMemoryCacheRead = bypassMemory;
                setupAction.SkipMemoryCacheWrite = bypassMemory;
            });
        Assert.That(record2, Is.Not.Null);

        // For good measure
        await Task.Delay(200);

        await cache.RemoveByTagAsync("foo",
            new FusionCacheEntryOptions
            {
                SkipMemoryCacheRead = bypassMemory,
                SkipMemoryCacheWrite = bypassMemory
            });

        // For good measure
        await Task.Delay(200);

        // Ensure it's gone
        var record3 = await cache.GetOrDefaultAsync<PocoA?>(key,
            setupAction =>
            {
                setupAction.SkipMemoryCacheRead = bypassMemory;
                setupAction.SkipMemoryCacheWrite = bypassMemory;
            });

        // THIS FAILS
        Assert.That(record3, Is.Null);
    }

Expected behavior

Tagged cache entries in L2 cache are removed.

Versions

I've encountered this issue on:

• FusionCache 2.1
• .NET version 9

Additional context

I enable this automatically in order to test that deserialization works. I don't use this in production.

[jodydonetti]

Hi @sebbarg , when calling RemoveByTag("my-tag") tagged entries are not necessarily removed, and even if so, not directly when calling the method.

For more on the design decisions and the tradeoffs, take a look here.

Let me know if it makes sense, thanks.