I would expect the performance to be the same in both cases and close to a cache that doesn't have a cache store.
Do you have eviction enabled? that might increase contingency on the cache store.
No, no eviction.
The entries have set lifetimes, but no expiration is reached in the test.
async FileCacheStore: 4s
async JdbmCacheStore: 47s
sync JdbmCacheStore: 60s
If the jdbm store does not yet exist, it is as fast as the file store.
If it exists, it is 10x slower.