Caching ISM configurations in the relayer

[tkporter]

Problem

ISMs tend to be pretty static, we can afford to cache ISM configurations for a given address

Solution

To have fewer RPCs when building metadata, cache ISM configs

[daniel-savu]

The goal of this task is twofold:

1. Since we want caches to be short lived, find a robust LRU cache library (maybe lru-rs) that ideally also supports TTLs for invalidating entries. Otherwise, implement wrapper logic to add / check TTLs when writing to the cache and when checking if there's a hit.

   • to test cache effectiveness, either the library or the wrapper should expose metrics that can be plugged into prometheus. Relayer metrics all expose call counts for all evm RPC methods used - those should see a dramatic drop as well.

2. Given the cache store, optimize the PendingMesage::prepare step for ISM metadata builders as much as possible

   • the cache map schema would look something like (contract_address, method, serialized_params) -> (serialized_call_result, entry_ttl), where method can be a string that's hardcoded in each MetadataBuilder implementation (e.g. validators_and_threshold for the MultisigISM)
   • MetadataBuilder would likely need two new methods to keep things generic:

   cache_call_result<T: Serialize, U: Serialize>(contract_address, method, serializable_params: T, call_result: U, ttl: <likely expressed as the timestamp of expiry>);
   
   get_cached_call_result<T: Deserialize>(contract_address, method, serialized_params) -> T;

   • These main calls to be cached, though there may be other easy wins (which should be cached as well in this task):
     • the validators_and_threshold call (here)
     • highest_known_leaf_index and get_merkle_leaf_id_by_message_id (here)
     • get_merkle_leaf_id_by_message_id (here)
     • get_offchain_verify_info (here)
     • modules_and_threshold (here)
     • in MessageMetadataBuilder, these calls

The implementation should be as generic as possible, to make it easy to add caching to other ISMs / network calls made by the agent in the future. TTLs can be hardcoded to 5 minutes.

[Mantas-M]

On it 🫡

[Mantas-M]

@daniel-savu Just a small clarification, you want to cache the entire ISMs during the building process? 🤔 Asking as doing so requires, everything of each InterchainSecurityModule implementation to be Serializable