Module cache 

64-shard query cache with three-tier invalidation.

Each shard is a parking_lot::RwLock<HashMap<QueryKey, CachedResult>>. Sharding reduces lock contention: concurrent reads to different query types never contend. The shard count is configurable (must be a power of two).

PN3 raw-byte retention

For queries with PERSISTENT = true, ShardedCache::insert_query serialises both the input key and the output value via postcard at insert time and stores the raw bytes alongside the typed value. This makes streaming the cache to disk in [iter_persistent] allocation-free after the fact — no re-serialisation is needed during save.

Entries whose serialised size exceeds QueryDbConfig::max_entry_size_bytes are not stored (soft skip — insert returns Ok(())). The caller’s computed value is unaffected because QueryDb::get returns the value directly without going through the cache for that invocation.

For PERSISTENT = false queries the raw bytes are set to empty slices and [iter_persistent] skips them.

Structs

CachedResult

A cached query result with dependency metadata for three-tier validation.

ShardedCache

64-shard query cache.