rdb-alpha

A Redis-protocol-compatible in-memory key-value store built from scratch in Python — no dependencies beyond the standard library.

Works with redis-cli, any Redis client library, and the included test suite.

Supported commands

Category	Commands
Basic	PING, ECHO, SET [EX], GET, DEL, EXISTS
Expiry	EXPIRE, TTL
Counters	INCR, DECR
Lists	LPUSH, RPUSH, LPOP, RPOP, LLEN, LRANGE
Hashes	HSET, HGET, HGETALL, HDEL
Admin	KEYS, DBSIZE, FLUSHALL, SAVE, INFO

Usage

# Start the server (default: 127.0.0.1:6380)
python server.py

# Custom host/port
python server.py --host 0.0.0.0 --port 6380

# Disable persistence
python server.py --dump ""

# Connect with redis-cli
redis-cli -p 6380 PING
redis-cli -p 6380 SET name "Biswajeet" EX 3600
redis-cli -p 6380 GET name
redis-cli -p 6380 KEYS "*"

Run tests

# In one terminal
python server.py

# In another
python test_server.py

How it works

• RESP3 protocol — the same wire format Redis uses; any Redis client connects unmodified
• Passive expiry — keys are evicted lazily on access, O(1) per operation
• JSON snapshots — SAVE writes an atomic snapshot; auto-save runs every 60s
• Async TCP — asyncio.start_server handles concurrent clients on a single thread
• Zero dependencies — stdlib only (asyncio, json, fnmatch, signal)

Design decisions

Why RESP3 over a custom protocol? Compatibility — any Redis client in any language works without modification.

Why passive expiry? O(1) per access, no background scan loop. Same trade-off Redis makes.

Why JSON for persistence? Human-readable and dependency-free. A natural extension is a compact binary format (like Redis RDB) for production use.