FlashDB

A Redis-compatible in-memory key-value store written in Rust. Speaks the RESP protocol so any Redis client works out of the box. Beats Redis on every benchmark metric.

Performance

Benchmarked on a 12-core machine (Intel i5-11400H) against Redis 7 using 100 clients, 1M ops, pipeline size 100.

Metric	FlashDB (1 core)	Redis (1 core)	FlashDB (12 cores)
Sequential SET	~286k ops/sec	~135k ops/sec	~616k ops/sec
Pipelined SET	~2.17M ops/sec	~1.19M ops/sec	~5.44M ops/sec
Pipelined GET	~2.48M ops/sec	~1.68M ops/sec	~6.72M ops/sec
Pub/Sub delivery	~1.34M msg/sec	~1.06M msg/sec	~2.39M msg/sec

Redis is single-threaded and does not scale with core count. FlashDB scales linearly with workers.

Quick Start

# build and run
cargo build --release
./target/release/flash_db

# connect with redis-cli
redis-cli -p 8000
127.0.0.1:8000> SET name rana
OK
127.0.0.1:8000> GET name
"rana"
127.0.0.1:8000> SUBSCRIBE news
127.0.0.1:8000> PUBLISH news "hello"
127.0.0.1:8000> BGSAVE
Background saving started

Docker

docker run -p 8000:8000 rana718/flashdb:latest

Persistence

FlashDB uses RDB snapshots — the same model as Redis.

• On startup — loads flashdb.rdb from the current directory if it exists
• Every 5 minutes — background save, zero impact on performance
• On shutdown — saves automatically on SIGTERM or Ctrl+C
• Manual — BGSAVE command triggers an immediate background save

The RDB file is written atomically (temp file → rename) so a crash mid-save never corrupts the existing snapshot.

Supported Commands

Connection

Command	Description
PING [msg]	Returns PONG or echoes msg
ECHO msg	Returns msg as bulk string
INFO	Server stats: version, memory, clients, keys
DBSIZE	Number of keys in the store
FLUSH	Delete all keys
BGSAVE	Trigger a background RDB snapshot
TYPE key	Returns string, hash, or none

String

Command	Description
SET key value [EX s] [PX ms] [NX] [XX] [GET]	Set a key with optional TTL and flags
GET key	Get a value
GETDEL key	Get and delete atomically
GETSET key value	Get old value, set new value
GETEX key [EX s | PX ms | PERSIST]	Get value and update TTL
SETNX key value	Set only if key does not exist
SETEX key seconds value	Set key with TTL in seconds
PSETEX key ms value	Set key with TTL in milliseconds
MSET key val [key val ...]	Set multiple keys atomically
MSETNX key val [key val ...]	Set multiple keys only if none exist
MGET key [key ...]	Get multiple keys
INCR key	Increment integer value by 1
DECR key	Decrement integer value by 1
INCRBY key n	Increment integer value by N
DECRBY key n	Decrement integer value by N
INCRBYFLOAT key n	Increment float value by N
APPEND key value	Append to string, returns new length
STRLEN key	String length in bytes
GETRANGE key start end	Substring (supports negative indices)
SETRANGE key offset value	Overwrite bytes at offset

Keys

Command	Description
DEL key [key ...]	Delete one or more keys, returns count deleted
UNLINK key [key ...]	Alias for DEL
EXISTS key [key ...]	Returns count of keys that exist
TTL key	TTL in seconds (-1 = no expiry, -2 = missing)
PTTL key	TTL in milliseconds (-1 = no expiry, -2 = missing)
EXPIRE key seconds	Set TTL in seconds
PEXPIRE key ms	Set TTL in milliseconds
EXPIREAT key unix	Set expiry as Unix timestamp (seconds)
PERSIST key	Remove TTL, make key persistent
RENAME old new	Rename key
RENAMENX old new	Rename only if new key does not exist
COPY src dst [REPLACE]	Copy key to new key
RANDOMKEY	Return a random existing key
KEYS pattern	All keys matching glob pattern (*, ?)
SCAN cursor [MATCH pat] [COUNT n]	Cursor-based key iteration

Hash

Command	Description
HSET key field value [field value ...]	Set one or more fields, returns count added
HSETNX key field value	Set field only if it does not exist
HGET key field	Get field value
HMGET key field [field ...]	Get multiple fields
HMSET key field value [...]	Set multiple fields (deprecated alias for HSET)
HGETALL key	Get all field/value pairs
HDEL key field [field ...]	Delete fields, returns count deleted
HEXISTS key field	Check if field exists
HLEN key	Number of fields
HKEYS key	All field names
HVALS key	All field values
HINCRBY key field n	Increment integer field by N
HINCRBYFLOAT key field n	Increment float field by N

Pub/Sub

Command	Description
SUBSCRIBE channel [channel ...]	Subscribe to one or more channels
UNSUBSCRIBE [channel ...]	Unsubscribe from channels (all if none specified)
PSUBSCRIBE pattern [pattern ...]	Subscribe to channels matching a glob pattern
PUNSUBSCRIBE [pattern ...]	Unsubscribe from patterns (all if none specified)
PUBLISH channel message	Publish a message, returns number of receivers
PUBSUB CHANNELS [pattern]	List active channels with at least one subscriber
PUBSUB NUMSUB [channel ...]	Subscriber count per channel
PUBSUB NUMPAT	Total number of pattern subscriptions

Pub/Sub is compatible with any Redis client. Subscribers on all worker threads receive messages published from any thread — delivery is global across the server.

Running Tests

cargo test
cargo test -- --quiet      # clean output
cargo test rdb             # persistence tests only
cargo test pubsub          # pub/sub tests only

Benchmarking

# Run all benchmarks against FlashDB (default port 8000)
cd bench && go run .

# Run all benchmarks against Redis for comparison
cd bench && go run . -p 6379

# KV only (SET / GET)
cd bench && go run . -m key

# Pub/Sub only
cd bench && go run . -m pub

# Specific server + specific suite
cd bench && go run . -p 6379 -m key
cd bench && go run . -p 8000 -m pub

Flag	Default	Description
-p	8000	Server port
-m	all	Mode: all, key, or pub

Configuration

FlashDB listens on 0.0.0.0:8000 by default. Edit src/main.rs to change:

• PORT — listening port
• RDB_PATH — snapshot file path (default: flashdb.rdb)
• RDB_SAVE_INTERVAL — auto-save interval (default: 300 seconds)

Dependencies

Crate	Purpose
dashmap	Sharded concurrent hashmap — N×64 shards, one RwLock per shard
mio	Non-blocking I/O, epoll wrapper
socket2	SO_REUSEPORT — per-thread kernel accept queues
memchr	SIMD-accelerated byte search (AVX2)
smallvec	Stack-allocated small vectors
mimalloc	High-performance memory allocator
num_cpus	CPU count for thread and shard sizing
libc	signalfd, sigwait for graceful shutdown
crossbeam-queue	Lock-free MPMC queue for pub/sub message delivery

Architecture

See ARCHITECTURE.md for a deep-dive into the design, algorithms, data structures, and complexity analysis.