HybridCache serialization issues when in-memory

[BrianVallelunga]

Description

I'm not sure if this is a bug or a misunderstanding, but when storing only locally, why is the data being serialized? I'd assume I could store any sort of object (interfaces, classes, etc) in a local, memory cache.

Reproduction Steps

My factory function returns a Task of an interface (IBloomFilter in this case). I'm passing the HybridCacheEntryFlags.DisableDistributedCache flag into the cache method as follows:

return hybridCache.GetOrCreate("BloomFilter", factory, HybridCacheEntryFlags.DisableDistributedCache)

Expected behavior

The object wouldn't go through serialization when caching locally in memory.

Actual behavior

An exception is thrown: System.NotSupportedException: Deserialization of interface or abstract types is not supported. Type 'BloomFilter.IBloomFilter'

Regression?

No response

Known Workarounds

No response

Configuration

.NET 9, HybridCache 9.2.0-preview1.25105.6

Other information

No response

[Mizuwokiru]

I haven't tested it yet but try to do this:

1. Use a type that has an attribute [ImmutableObject(true)].
2. Use DisableDistributedCache and DisableLocalCacheWrite flags. According to the code here it seems you need DisableLocalCacheWrite flag too to disable local cache serialization.

[BrianVallelunga]

Thanks @Mizuwokiru , but if I set DisableLocalCacheWrite along with DisableDistributedCache then I'm not caching anything at all, right?

[jodydonetti]

To the best of my knowledge, HybridCache tries to be consistent with IDistributedCache in not returning live references, to "avoid surprises". To do that, it serialize/deserialize the result to clone it, basically.

I remember at the beginning there was supposed to be an option to disable this behavior, but right now I don't see it in the docs.

Hope this helps.

[BrianVallelunga]

It would be nice if it could provide a true superset of IMemoryCache's abilities. While I can still use that in my code, using a single caching mechanism would be ideal.

[jodydonetti]

Hi @BrianVallelunga , if in fact there's no way to do that with HybridCache for now, you can take a look at FusionCache (creator here, shameless plug).

You can use it either directly or, if you prefer staying with the HybridCache abstraction, via the available adapter.

Hope this helps.

[snakex64]

Hello! I added a PR to fix this by adding a new "DisableLocalCacheSerialization" flag. The flag is temporarily not in the right place since it required changing the runtime repo (the enum is in the "Abstractions" project, which is not in the same repo as the actual implementation).

Like I described in the PR, I wanted to get the conversation going again before spending more time on it. Feel free to give your opinion :)

#7641

[svick]

I am wondering whether adding a flag for this is the best option. Wouldn't an attribute on the serialized type be better? ([ImmutableObject] already works for sealed classes and structs for this purpose, but I don't think it makes sense for interfaces, so I would create a new attribute type for this.)

[snakex64]

I thought about just adding the existing [ImmutableObject] in my own code but it seemed dirty to have to go through all the cache types that we have to add this, or types that I might not even own which I would be forced to wrap them. I'm also afraid to forget it in the future and start having either performance issues or weird behavior if I have objects that are not intended to be serialized/deserialized.

As opposed to having an option on each item, which can easily have a default value (I almost never use the HybridCache object directly, so I can have different default values for different context, automatically add tags based on the current DI scope (which the MemoryCache doesn't support), etc )

[svick]

@snakex64 Yeah, that makes sense. In that case, a new flag on HybridCacheEntryFlags or a new option on HybridCacheEntryOptions makes sense to me.

That then encounters the difficulty of changing both dotnet/runtime and dotnet/extensions parts. I have a plan to address that for .Net 12 (it's too late to change APIs in dotnet/runtime for .Net 11 anyway). But that means it's going to be several months before this can move forward.

@jodydonetti I see that FusionCache has a very similar feature, EnableAutoClone, but the default is the opposite than what DefaultHybridCache has. I assume that changing the default (at least in the HybridCache adapter) is an unacceptable breaking change for you? Would it make sense to have a bool? DisableLocalCacheSerialization (possibly with a different name) on HybridCacheEntryOptions? The null value would preserve the default, false would force enabling serialization (equivalent to EnableAutoClone = true) and true would force disabling serialization (EnableAutoClone = false).