Question about HybridCache value type

[Yiling-J]

The HybridCache part of CacheLib is very intersting and I'm considering implementing similar thing in my Go cache package. I'm not expert of C++ and can't find answer in documentation, so I think ask here is the best. So my question is, does HybridCache support any type of value? From the documentation I think HybridCache will copy memory data to NVM, what if value is a struct contains pointer or vector members, will HybridCache copy pointer address? Currently my Go package is generic so value type can be anything, I think I need to limit value types to make HybridCache work in Go.

[haowu14]

Hybrid cache (and traditional cachelib) doesn't support types. It's just byte strings so no pointers allowed there.

Object-cache is only used for DRAM cache (no flash) and you can cache c++ objects.

[Yiling-J]

Thanks for the explanation! Seems like I can't find documentations about Object-cache, is that objcache2 in experimental? And Object-cache is only used for DRAM cache because it's not safe to marshal object to byte? BTW cachelib's trace and Architecture Guide are very useful! I already use the trace in my cache package benchmark and try to implement hybrid cache based on the Architecture Guide.

[haowu14]

Before Object-Cache was introduced, the users would serialize their customized datastructure into byte strings and use CacheLib. For some users, this serialization and deserialization is too expensive, especially for users with frequent updates. Therefore Object-Cache was introduced, aiming to reduce this cost.

But if we are going to move data to flash, we'd need to serialized the data anyway, so we might as well just use regular CacheLib.

[Yiling-J]

@haowu14 Actually I think Object-Cache with hybrid has one benefit, data are deserialized and insert to memory before return to client, which means hit memory part of hybrid cache will avoid the cost of deserialization. If deserialization is expensive this can improve performance compared to regular byte cache.