Dragonfly

A novel memory store that supports Redis and Memcached commands. For more detailed status of what's implemented - see below.

Features include:

1. High throughput reaching millions of QPS on a single node.
2. TLS support.
3. Pipelining mode.
4. A novel cache design, which does not require specifying eviction policies.
5. Memory efficiency that can save 20-40% for regular workloads and even more for cache like workloads

Running

dragonfly requires Linux OS version 5.11 or later. Ubuntu 20.04.4 or 22.04 fit these requirements.

If built locally just run:

./dragonfly --logtostderr

or with docker:

docker pull ghcr.io/dragonflydb/dragonfly:latest && \
docker tag ghcr.io/dragonflydb/dragonfly:latest dragonfly

docker run --network=host --rm dragonfly

Some systems may require adding --ulimit memlock=-1 to docker run options.

We support redis command arguments where applicable. For example, you can run: docker run --network=host --rm dragonfly --requirepass=foo --bind localhost.

dragonfly currently supports the following commandline options:

• port
• bind
• requirepass
• maxmemory
• memcache_port - to enable memcached compatible API on this port. Disabled by default.
• dir - by default, dragonfly docker uses /data folder for snapshotting. You can use -v docker option to map it to your host folder.
• dbfilename
• dbnum - maximum number of supported databases for select.
• keys_output_limit - maximum number of returned keys in keys command. Default is 8192. We truncate the output to avoid blowup in memory when fetching too many keys.

for more options like logs management or tls support, run dragonfly --help.

Building from source

I've tested the build on Ubuntu 20.04+. Requires: CMake, Ninja, boost, libunwind8-dev

# to install dependencies
sudo apt install ninja-build libunwind-dev libboost-fiber-dev libssl-dev

git clone --recursive https://github.com/dragonflydb/dragonfly && cd dragonfly

# another way to install dependencies
./helio/install-dependencies.sh

# Configure the build
./helio/blaze.sh -release

cd build-opt && ninja dragonfly  # build

Roadmap and milestones

We are planning to implement most of the APIs 1.x and 2.8 (except the replication) before we release the project to source availability on github. In addition, we will support efficient expiry (TTL) and cache eviction algorithms.

The next milestone afterwards will be implementing redis -> dragonfly and dragonfly<->dragonfly replication.

For dragonfly-native replication we are planning to design a distributed log format that will support order of magnitude higher speeds when replicating.

Commands that I wish to implement after releasing the initial code:

• PUNSUBSCRIBE
• PSUBSCRIBE
• HYPERLOGLOG
• SCRIPT DEBUG
• OBJECT
• DUMP/RESTORE
• CLIENT

Their priority will be determined based on the requests from the community. Also, I will omit keyspace notifications. For that I would like to deep dive and learn exact the exact needs for this API.

Milestone - "Source Available"

API 1.0

• String family
  • SET
  • SETNX
  • GET
  • DECR
  • INCR
  • DECRBY
  • GETSET
  • INCRBY
  • MGET
  • MSET
  • MSETNX
  • SUBSTR
• Generic family
  • DEL
  • ECHO
  • EXISTS
  • EXPIRE
  • EXPIREAT
  • KEYS
  • PING
  • RENAME
  • RENAMENX
  • SELECT
  • TTL
  • TYPE
  • SORT
• Server Family
  • AUTH
  • QUIT
  • DBSIZE
  • BGSAVE
  • SAVE
  • DEBUG
  • EXEC
  • FLUSHALL
  • FLUSHDB
  • INFO
  • MULTI
  • SHUTDOWN
  • LASTSAVE
  • SLAVEOF/REPLICAOF
  • SYNC
• Set Family
  • SADD
  • SCARD
  • SDIFF
  • SDIFFSTORE
  • SINTER
  • SINTERSTORE
  • SISMEMBER
  • SMOVE
  • SPOP
  • SRANDMEMBER
  • SREM
  • SMEMBERS
  • SUNION
  • SUNIONSTORE
• List Family
  • LINDEX
  • LLEN
  • LPOP
  • LPUSH
  • LRANGE
  • LREM
  • LSET
  • LTRIM
  • RPOP
  • RPOPLPUSH
  • RPUSH
• SortedSet Family
  • ZADD
  • ZCARD
  • ZINCRBY
  • ZRANGE
  • ZRANGEBYSCORE
  • ZREM
  • ZREMRANGEBYSCORE
  • ZREVRANGE
  • ZSCORE
• Not sure whether these are required for the initial release.
  • BGREWRITEAOF
  • MONITOR
  • RANDOMKEY
  • MOVE

API 2.0

• List Family
  • BLPOP
  • BRPOP
  • BRPOPLPUSH
  • LINSERT
  • LPUSHX
  • RPUSHX
• String Family
  • SETEX
  • APPEND
  • PREPEND (dragonfly specific)
  • BITCOUNT
  • BITFIELD
  • BITOP
  • BITPOS
  • GETBIT
  • GETRANGE
  • INCRBYFLOAT
  • PSETEX
  • SETBIT
  • SETRANGE
  • STRLEN
• HashSet Family
  • HSET
  • HMSET
  • HDEL
  • HEXISTS
  • HGET
  • HMGET
  • HLEN
  • HINCRBY
  • HINCRBYFLOAT
  • HGETALL
  • HKEYS
  • HSETNX
  • HVALS
  • HSCAN
• PubSub family
  • PUBLISH
  • PUBSUB
  • PUBSUB CHANNELS
  • SUBSCRIBE
  • UNSUBSCRIBE
  • PSUBSCRIBE
  • PUNSUBSCRIBE
• Server Family
  • WATCH
  • UNWATCH
  • DISCARD
  • CLIENT LIST/SETNAME
  • CLIENT KILL/UNPAUSE/PAUSE/GETNAME/REPLY/TRACKINGINFO
  • COMMAND
  • COMMAND COUNT
  • COMMAND GETKEYS/INFO
  • CONFIG GET/REWRITE/SET/RESETSTAT
  • MIGRATE
  • ROLE
  • SLOWLOG
  • PSYNC
  • TIME
  • LATENCY...
• Generic Family
  • SCAN
  • PEXPIREAT
  • PEXPIRE
  • DUMP
  • EVAL
  • EVALSHA
  • OBJECT
  • PERSIST
  • PTTL
  • RESTORE
  • SCRIPT LOAD/EXISTS
  • SCRIPT DEBUG/KILL/FLUSH
• Set Family
  • SSCAN
• Sorted Set Family
  • ZCOUNT
  • ZINTERSTORE
  • ZLEXCOUNT
  • ZRANGEBYLEX
  • ZRANK
  • ZREMRANGEBYLEX
  • ZREMRANGEBYRANK
  • ZREVRANGEBYSCORE
  • ZREVRANK
  • ZUNIONSTORE
  • ZSCAN
• HYPERLOGLOG Family
  • PFADD
  • PFCOUNT
  • PFMERGE

Memchache API

• set
• get
• replace
• add
• stats (partial)
• append
• prepend
• delete
• flush_all
• incr
• decr
• version
• quit

Random commands we implemented as decorators along the way:

• ROLE (2.8) decorator for for master without replicas
• UNLINK (4.0) decorator for DEL command
• BGSAVE (decorator for save)
• FUNCTION FLUSH (does nothing)

Milestone "Stability"

APIs 3,4,5 without cluster support, without modules, without memory introspection commands. Without geo commands and without support for keyspace notifications, without streams. Design config support. ~10-20 commands overall... Probably implement cluster-API decorators to allow cluster-configured clients to connect to a single instance.

• HSTRLEN

Design decisions along the way

Novel cache design

Redis allows choosing 8 different eviction policies using maxmemory-policy flag.

Dragonfly has one unified adaptive caching algorithm that is more memory efficient than of Redis. You can enable caching mode by passing --cache_mode=true flag. Once this mode is on, Dragonfly will evict items when it reaches maxmemory limit.

Expiration deadlines with relative accuracy

Expiration ranges are limited to ~4 years. Moreover, expiration deadlines with millisecond precision (PEXPIRE/PSETEX etc) will be rounded to closest second for deadlines greater than 134217727ms (approximately 37 hours). Such rounding has less than 0.001% error which I hope is acceptable for large ranges. If it breaks your use-cases - talk to me or open an issue and explain your case.

For more detailed differences between this and Redis implementations see here.

Native Http console and Prometheus compatible metrics

By default Dragonfly also allows http access on its main TCP port (6379). That's right, you can use for Redis protocol and for HTTP protocol - type of protocol is determined automatically during the connection initiation. Go ahead and try it with your browser. Right now it does not have much info but in the future we are planning to add there useful debugging and management info. If you go to :6379/metrics url you will see some prometheus compatible metrics.

Important! Http console is meant to be accessed within a safe network. If you expose Dragonfly's TCP port externally, it is advised to disable the console with --http_admin_console=false or --nohttp_admin_console.