I just released lettuce 3.3.1.Final and lettuce 4.0.Final. I'm going to tell you in this post more about 4.0. You can find the full details about 3.3.1.Final and 4.0.Final on Github.

lettuce 4.0 is a major release that introduces numerous changes like stateful connections, the reactive API and many more. Lettuce 4.0 includes all features from lettuce 3.3.

Highlights of lettuce 4.0.Final

  • Reactive API
  • Stateful connections
  • Cross-slot command execution
  • Node Selection API/Execution of commands on multiple cluster nodes
  • ReadFrom Settings/Redis Cluster slave reads
  • Custom commands

This release contains some breaking changes. You may want to consult the wiki at Migration from 3.x to 4.x to check the migration guide.

All Redis...Connection and Redis...AsyncConnection interfaces are deprecated and replaced by new ...Commands interfaces.

The cluster API was extended to run a command on multiple nodes and invocation to multi-key commands DEL, MGET, MSET and MSETNX perform automatic pipelining if the keys belong to different slots/masters.

A couple of changes are breaking changes, and you need most likely to adopt your code to use lettuce 4.0. lettuce 4.0 dropped Java 6 and 7 support and requires Java 8 to run. lettuce 4.0 needs Java 8 and cannot be used with Java 6 or 7.

Reactive API

Lettuce provides since its genesis two API's: Sync and async.
Now comes a third one: Reactive.
The reactive API uses rx-java and every command on the reactive API returns an Observable.

StatefulRedisConnection<String, String> connection = client.connect();
RedisReactiveCommands<String, String> reactive = stateful.reactive();

Observable observable = reactiveApi.keys("*");

// more sophisticated


The command is only executed on a subscription to the Observable.
Commands returning a collection, such as Lists or Sets, return Observables that provide the element type. The reactive API covers the same commands as the synchronous/asynchronous API's.

Read more: Reactive API

Rearchitecting the API

Before 4.0, connection resources (sockets, events) were bound to the particular API.
If one wanted to use a different API, he had to create another connection to Redis. This coupling is loosed now. By calling connect() you will no longer get a synchronous connection, you will get a StatefulRedisConnection with the access to the synchronous, asynchronous and reactive API.
All commands are executed using netty and it does not matter, from which API you come.

3.x code:

RedisConnection connection = client.connect();

4.x code:

StatefulRedisConnection stateful = client.connect();

RedisCommands commands = stateful.sync();

// still working
RedisAsyncConnection connection = client.connectAsync();

The other connect methods like connectAsync and connectSentinelAsync are
deprecated but remain unchanged.

Breaking changes in connect methods are:

  • RedisClient.connect (provides a StatefulRedisConnection)
  • RedisClient.connectPubSub (provides a StatefulRedisPubSubConnection)
  • RedisClusterClient.connectCluster (provides a StatefulRedisClusterConnection)

New connect methods:

  • RedisClient.connectSentinel (provides a StatefulRedisSentinelConnection)

New segregated command interfaces

Starting with reactive API's, another 13 interfaces will be provided with lettuce.
This change increases the count of types within the com.lambdaworks.redis package and the package gets messier again. In combination with the stateful connection the original ...Connection or ...AsyncConnection interfaces no longer reflect the real purpose. New Commands interfaces provide the same functionality and are located in api.sync and api.async packages (respective cluster.api.sync, cluster.api.async and so on for the Redis Cluster client and PubSub).

The following interfaces are deprecated and substituted by new ...Commands interfaces:

  • RedisHashesAsyncConnection
  • RedisHashesConnection
  • RedisHLLAsyncConnection
  • RedisHLLConnection
  • RedisKeysAsyncConnection
  • RedisKeysConnection
  • RedisListsAsyncConnection
  • RedisListsConnection
  • RedisScriptingAsyncConnection
  • RedisScriptingConnection
  • RedisSentinelAsyncConnection
  • RedisServerAsyncConnection
  • RedisServerConnection
  • RedisSetsAsyncConnection
  • RedisSetsConnection
  • RedisSortedSetsAsyncConnection
  • RedisSortedSetsConnection
  • RedisStringsAsyncConnection
  • RedisStringsConnection
  • RedisClusterConnection
  • RedisConnection
  • RedisClusterAsyncConnection
  • RedisAsyncConnection
  • BaseRedisConnection
  • BaseRedisAsyncConnection

See Migration from 3.x to 4.x for the migration matrix.

New API's

  • StatefulClusterConnection
  • StatefulRedisPubSubConnection
  • StatefulClusterConnection
  • StatefulRedisSentinelConnection
  • RedisPubSubAsyncConnection and RedisPubSubConnection

API Changes

  • readOnly and readWrite changed from String return type to RedisFuture<String>. The connection state is maintained by the future completion.
  • Moved CommandOutput from com.lambdaworks.redis.protocol to com.lambdaworks.redis.output
  • Moved SetArgs from com.lambdaworks.redis.protocol to com.lambdaworks.redis
  • All connections are AutoCloseable so you can handle connections using try-with-resources.
  • RedisFutures are based on CompleteableFuture and throw now any occurred exception when accessing the value using get().

Exceptions are passed down the CompletionStages.

Client factory methods

RedisClient and RedisClusterClient provide factory methods (create) to create new instances. This is, to get flexibility by reducing the number of constructors and in preparation for reusable ClientResources which will be added with lettuce 4.1.

The constructors of RedisClient and RedisClusterClient are deprecated and will be removed in future versions.

RedisClient client = RedisClient.create();

RedisClient client = RedisClient.create("redis://localhost/");

RedisClient client = RedisClient.create(RedisURI.Builder.redis("localhost", 6379).build());

RedisClusterClient client = RedisClusterClient.create("redis://localhost/");

RedisClusterClient client = RedisClusterClient.create(RedisURI.Builder.redis("localhost", 6379).build());

Cross-slot command execution

Regular Redis Cluster commands are limited to single-slot keys, basically either single key commands or multi-key commands that share the same hash slot of their keys.

The cross slot limitation can be mitigated by using the advanced cluster API for some multi-key commands. Commands that operate on keys with different slots are decomposed into multiple commands.
The single commands are fired in a fork/join fashion. The commands are issued concurrently to avoid
synchronous chaining. Results are synchronized before the command is completed (from a user perspective).

Following commands are supported for cross-slot command execution:

  • DEL: Delete the KEYs from the affected cluster. Returns the number of keys that were removed
  • MGET: Get the values of all given KEYs. Returns the values in the order of the keys.
  • MSET: Set multiple key/value pairs for all given KEYs. Returns always OK.

Cross-slot command execution is available on the following APIs:

  • RedisAdvancedClusterCommands
  • RedisAdvancedClusterAsyncCommands
  • RedisAdvancedClusterReactiveCommands

Node Selection API/Execution of commands on multiple cluster nodes

The advanced cluster API allows to select nodes and run commands on the node selection. This API is subject to incompatible changes in a future release. The API is exempt from any compatibility guarantees made by lettuce. The current state implies nothing about the quality or performance of the API in question, only the fact that it is not "API-frozen". All commands are sent concurrently to the Redis nodes, meaning you do not have to wait until the commands have finished to trigger the next command. That behavior is independent of the API you're using. The Node Selection API is available from the synchronous and asynchronous command interfaces:


RedisAdvancedClusterAsyncCommands<String, String> async = clusterClient.connect().async();
AsyncNodeSelection<String, String> slaves = async.slaves();

AsyncExecutions<List<String>> executions = slaves.commands().keys("*");
executions.stream().forEach(result -> result.thenAccept(keys -> System.out.println(keys)));


RedisAdvancedClusterCommands<String, String> sync = clusterClient.connect().sync();
NodeSelection<String, String> sync = connection.slaves();

Executions<List<String>> executions = slaves.commands().keys("*");
executions.stream().forEach(result -> result.thenAccept(keys -> System.out.println(keys)));

Commands are dispatched to the nodes within the selection, the result (CompletionStage or the value) is available from the AsyncExecutions/Executions result holders.
This API is a technical preview, so your feedback is highly appreciated.

Read more: Redis Cluster

ReadFrom Settings/Redis Cluster slave reads

The ReadFrom setting describes how lettuce routes read operations to the members of a Redis Cluster.

By default, lettuce routes its read operations to the master node. Reading from the master returns the most recent version of the data because write operations are issued to the single master node. Reading from masters guarantees strong consistency.

The ReadFrom setting can be set to one of the following presets:

  • MASTER Default mode. Read from the current master node.
  • MASTER_PREFERRED Read from the master, but if it is unavailable, read from slave nodes.
  • SLAVE Read from slave nodes.
  • NEAREST Read from any node of the cluster with the lowest latency.

Custom read settings can be implemented by extending the com.lambdaworks.redis.ReadFrom class.

Read more: ReadFrom Settings

Custom commands

Lettuce covers nearly all Redis commands. Redis development is an ongoing process, and some commands are not covered by lettuce meaning there are use cases that require invocation of custom commands or custom outputs. lettuce 4.x allows you to trigger own commands. That API is used by lettuce itself to dispatch commands and requires some knowledge of how commands are constructed and dispatched within lettuce.

StatefulRedisConnection<String, String> connection = redis.getStatefulConnection();

RedisCommand<String, String, String> command = new Command<>(CommandType.PING,
                                            new StatusOutput<>(new Utf8StringCodec()));

AsyncCommand<String, String, String> async = new AsyncCommand<>(command);

// async instanceof CompletableFuture == true

Read more: Custom commands, outputs and command mechanics

Codec API improvements

The RedisCodec API was aligned to a consistent interchange type and migrated to an interface.
The RedisCodec interface accepts and returns ByteBuffer for data interchange. A ByteBuffer is not opinionated about the source of the underlying bytes and such it does not require users to duplicate existing data as it was enforced by a byte[]. Lettuce provides UTF-8 and byte[] codecs and allows users to create and use their own codecs. XML, JSON and Java-serialization are good examples for codecs.

This release also brings a value compressor which allows you to compress values using GZIP or Deflate compressions. Value compression is transparent and can be used with any codec.

RedisCommands<String, Object> connection = client.connect(
           CompressionCodec.valueCompressor(new SerializedObjectCodec(), GZIP)).sync(); 

RedisCommands<String, String> connection = client.connect(
              CompressionCodec.valueCompressor(new Utf8StringCodec(), DEFLATE)).sync(); 

Read more: Codecs

Updated dependencies

  • rxjava 1.0.14 (new)
  • Google Guava 17.0 -> 18.0
  • netty 4.0.28.Final 4.0.30.Final
  • commons-pool2 2.2 -> 2.4.2


  • Migrate RedisFuture to CompletionStage #48
  • Drop support for Java 6 and Java 7 #50
  • Pipelining for certain cluster commands #66
  • Reactive support #68
  • Provide a stateful Redis connection and decouple sync/async API from connection resources #75
  • Move segregated API interfaces to own packages #76
  • Improve HLL command interface #77
  • Advanced Cluster API (async) #78
  • Provide a sync API for Redis Sentinel #79
  • Remove Java 6/7 parts of JavaRuntime and use netty's SslContextBuilder #85
  • Support geo commands in lettuce 4.0 #87
  • Run certain commands from the advanced cluster connection on multiple hosts #106
  • Allow limiting the request queue size #115
  • Improve Codec API #118
  • Allow to read from master/slave/nearest node when using Redis Cluster #114
  • Documentation of custom commands #122
  • Implement a CompressionCodec for GZIP and Deflate compression #127
  • Implement synchronous multi-node execution API #129
  • Use LinkedHashMap instead of HashMap for Map outputs #133 (thanks to @longkerdandy)
  • Implement client factory methods (RedisClient.create, RedisClusterClient.create) #136


  • CI: Build ran into OutOfMemoryError: Java heap space #84
  • Use Sucess instead of Void in the reactive API #128
  • GEOADD passes long/lat parameters in the wrong order to Redis #134 (thanks to @IdanFridman)
  • Strip username from URI userinfo when creating a RedisURI with a username #131 (thanks to @jsiebens)
  • GeoArgs not evaluated when calling georadiusbymember(...) #142
  • Guava's CacheBuilder missing in shaded jar #143


  • Documentation for 4.0 #83
  • Improve performance in 4.0 #91
  • Update Dependencies for lettuce 4.0 #116
  • Documentation of custom commands #122
  • Client-specific client options and reduce visibility of AbstractClient.setOptions #135

For complete information on lettuce see the websites:


Maven coordinates:




Any feedback is appreciated or file an issue on GitHub.