Persist

• A log-structured key-value storage engine, written in C, inspired by Riak's Bitcask paper
• Designed to store variable-length key-value pairs
• Supports the following operations: put, get, delete

How it works

• Key-value pairs are represented as byte-arrays, and stored on disk for persistence
• Keys are additionally stored in an in-memory hashtable (keydir) for quick lookups
• All writes are append-only operations, to minimize IOs
• Deletes create tombstones, which are cleaned up by the merge operation
• Each persist directory contains a .metadata file to keep track of the latest file being written to

Usage

• make persist - creates the persist binary
• open <dirname> - opens a persist directory
• put <key> <value> - stores key-value pair
• get <key> - retrieves the value for a key
• delete <key> - deletes key-value pair
• merge - removes stale entries from the directory
• exit - stops the storage engine

Credit

• Images taken shamelessly from the Bitcask paper and from Arpit Bhayani's blog