kvcache

kvcache

kvcache implements a simple key/value datastore for a particular use case:

• Keys and values are just bytes
• Keys are small (10-50 bytes) and values are large (kilobytes)
• Keys and values only need to be accessed for a fixed time window

General implementation notes:

• Key/value pairs have a fixed expiration duration
• Key/value pairs are immutable, once written (until expired)
• Key/value pairs are stored on disk in a rotating set of fixed-size append-only logs
• The keys are associated with offsets into the log by an in-memory hashtable (can be reconstructed from an index written alongside each log)

Future optimizations

• The DB mutex is a huge lock -> bottleneck
  • Shard the memCache, refCache to use more granular locks
  • Pull some ideas from the lock-free hash table literature
• Now that RefMap is gone, I think we can get rid of the SHA-1 key hashing and just use keys everywhere.