Graal Native Image¶

This section explains how to use Lettuce with Graal Native Image compilation.

Why Create a Native Image?¶

The GraalVM native-image tool enables ahead-of-time (AOT) compilation of Java applications into native executables or shared libraries. While traditional Java code is just-in-time (JIT) compiled at run time, AOT compilation has two main advantages:

First, it improves the start-up time since the code is already pre-compiled into efficient machine code.
Second, it reduces the memory footprint of Java applications since it eliminates the need to include infrastructure to load and optimize code at run time.

There are additional advantages such as more predictable performance and less total CPU usage.

Building Native Images¶

Native images assume a closed world principle in which all code needs to be known at the time the native image is built. Graal's SubstrateVM analyzes class files during native image build-time to determine what bytecode needs to be translated into a native image. While this task can be achieved to a good extent by analyzing static bytecode, it’s harder for dynamic parts of the code such as reflection. When using reflective access or Java proxies, the native image build process requires a little bit of help so it can include parts that are required during runtime.

Lettuce ships with configuration files that specifically describe which classes are used by Lettuce during runtime and which Java proxies get created.

Starting as of Lettuce 5.3.2, the following configuration files are available:

META-INF/native-image/io.lettuce/lettuce-core/native-image.properties
META-INF/native-image/io.lettuce/lettuce-core/proxy-config.json
META-INF/native-image/io.lettuce/lettuce-core/reflect-config.json

Those cover Lettuce operations for RedisClient and RedisClusterClient.

Depending on your configuration you might need additional configuration for Netty, HdrHistogram (metrics collection), Reactive Libraries, and dynamic Redis Command interfaces.

HdrHistogram/Command Latency Metrics¶

Lettuce uses HdrHistogram and LatencyUtils to accumulate metrics. You can use your application without these. If you want to use Command Latency Metrics, please add the following lines to your own reflect-config.json file:

  {
    "name": "org.HdrHistogram.Histogram"
  },
  {
    "name": "org.LatencyUtils.PauseDetector"
  }

Dynamic Command Interfaces¶

You can use Dynamic Command Interfaces when compiling your code to a GraalVM Native Image. GraalVM requires two information as Lettuce inspects command interfaces using reflection and it creates a Java proxy:

Add the command interface class name to your reflect-config.json using ideally allDeclaredMethods:true.
Add the command interface class name to your proxy-config.json

**`reflect-config.json`**

[
  {
    "name": "com.example.MyCommands",
    "allDeclaredMethods": true
  },
]

**`proxy-config.json`**

[
  ["com.example.MyCommands"]
]

Reactive Libraries¶

If you decide to use a specific reactive library with dynamic command interfaces, please add the following lines to your reflect-config.json file, depending on the presence of Rx Java 1-3:

  {
    "name": "rx.Completable"
  },
  {
    "name": "io.reactivex.Flowable"
  },
  {
    "name": "io.reactivex.rxjava3.core.Flowable"
  }

Limitations¶

For now, native images must be compiled with --report-unsupported-elements-at-runtime to ignore missing Method Handles and annotation synthetization failures.

Netty Config¶

To properly start up the netty stack, the following reflection configuration is required for netty and the JDK in reflect-config.json:

  {
    "name":"io.netty.util.internal.shaded.org.jctools.queues.BaseMpscLinkedArrayQueueColdProducerFields",
    "fields":[{"name":"producerLimit","allowUnsafeAccess" :  true}]
  },
  {
    "name":"io.netty.util.internal.shaded.org.jctools.queues.BaseMpscLinkedArrayQueueConsumerFields",
    "fields":[{"name":"consumerIndex","allowUnsafeAccess" :  true}]
  },
  {
    "name":"io.netty.util.internal.shaded.org.jctools.queues.BaseMpscLinkedArrayQueueProducerFields",
    "fields":[{"name":"producerIndex", "allowUnsafeAccess" :  true}]
  },
  {
    "name":"io.netty.util.internal.shaded.org.jctools.queues.MpscArrayQueueConsumerIndexField",
    "fields":[{"name":"consumerIndex", "allowUnsafeAccess" :  true}]
  },
  {
    "name":"io.netty.util.internal.shaded.org.jctools.queues.MpscArrayQueueProducerIndexField",
    "fields":[{"name":"producerIndex", "allowUnsafeAccess" :  true}]
  },
  {
    "name":"io.netty.util.internal.shaded.org.jctools.queues.MpscArrayQueueProducerLimitField",
    "fields":[{"name":"producerLimit","allowUnsafeAccess" :  true}]
  },
  {
    "name":"java.nio.Buffer",
    "fields":[{"name":"address", "allowUnsafeAccess":true}]
  },
  {
    "name":"java.nio.DirectByteBuffer",
    "fields":[{"name":"cleaner", "allowUnsafeAccess":true}],
    "methods":[{"name":"<init>","parameterTypes":["long","int"] }]
  },
  {
    "name":"io.netty.buffer.AbstractReferenceCountedByteBuf",
    "fields":[{"name":"refCnt", "allowUnsafeAccess":true}]
  },
  {
    "name":"io.netty.buffer.AbstractByteBufAllocator",
    "allPublicMethods": true,
    "allDeclaredFields":true,
    "allDeclaredMethods":true,
    "allDeclaredConstructors":true
  },
  {
    "name":"io.netty.buffer.PooledByteBufAllocator",
    "allPublicMethods": true,
    "allDeclaredFields":true,
    "allDeclaredMethods":true,
    "allDeclaredConstructors":true
  },
  {
    "name":"io.netty.channel.ChannelDuplexHandler",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name":"io.netty.channel.ChannelHandlerAdapter",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.channel.ChannelInboundHandlerAdapter",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.channel.ChannelInitializer",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.channel.ChannelOutboundHandlerAdapter",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.channel.DefaultChannelPipeline$HeadContext",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.channel.DefaultChannelPipeline$TailContext",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.channel.socket.nio.NioSocketChannel",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name": "io.netty.handler.codec.MessageToByteEncoder",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  },
  {
    "name":"io.netty.util.ReferenceCountUtil",
    "allPublicMethods": true,
    "allDeclaredConstructors":true
  }

Functionality¶

We don’t have found a way yet to invoke default interface methods on proxies without MethodHandle. Hence the NodeSelection API (masters(), all() and others on RedisAdvancedClusterCommands and RedisAdvancedClusterAsyncCommands) do not work.