fn insert(&self, l2_block_number: L2BlockNumber, hashed_key: H256, value: StorageValue) {
        let lock = self.0.read().expect("values cache is poisoned");
        if lock.valid_for == l2_block_number {
            lock.values.insert(
                hashed_key,
                TimestampedStorageValue {
                    value,
                    loaded_at: l2_block_number,
                },
            );
        } else {
            CACHE_METRICS.stale_values.inc();
        }
    }
Caches `value` for `key`, but only if the cache currently holds values for `l2_block_number`.
core/lib/state/src/postgres/mod.rs