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docs: add default threads count about NioEventLoopGroup #3221

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docs: add default threads count about NioEventLoopGroup
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19 changes: 13 additions & 6 deletions docs/advanced-usage.md
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Expand Up @@ -97,12 +97,19 @@ instance needs to be shut down once it’s not used anymore.

The basic configuration options are listed in the table below:

| Name | Method | Default |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------|------------------------|
| **I/O Thread Pool Size** | `ioThreadPoolSize` | `Number of processors` |
| The number of threads in the I/O thread pools. The number defaults to the number of available processors that the runtime returns (which, as a well-known fact, sometimes does not represent the actual number of processors). Every thread represents an internal event loop where all I/O tasks are run. The number does not reflect the actual number of I/O threads because the client requires different thread pools for Network (NIO) and Unix Domain Socket (EPoll) connections. The minimum I/O threads are `3`. A pool with fewer threads can cause undefined behavior. | | |
| **Computation Thread Pool Size** | `comput ationThreadPoolSize` | `Number of processors` |
| The number of threads in the computation thread pool. The number defaults to the number of available processors that the runtime returns (which, as a well-known fact, sometimes does not represent the actual number of processors). Every thread represents an internal event loop where all computation tasks are run. The minimum computation threads are `3`. A pool with fewer threads can cause undefined behavior. | | |
| Name | Method | Default |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------|-------------|
| **I/O Thread Pool Size** | `ioThreadPoolSize` | `See below` |
| The number of threads in the I/O thread pools. Every thread represents an internal event loop where all I/O tasks are run. The number does not reflect the actual number of I/O threads because the client requires different thread pools for Network (NIO) and Unix Domain Socket (EPoll) connections. The minimum I/O threads are `2`. | | |
| **Computation Thread Pool Size** | `comput ationThreadPoolSize` | `See below` |
| The number of threads in the computation thread pool. Every thread represents an internal event loop where all computation tasks are run. The minimum computation threads are `2`. | | |

#### Default thread pool size

Unless configured otherwise by the settings above, the number of threads (for both computation and I/O) is determined in the following order:
* if there is an environment variable setting for `io.netty.eventLoopThreads` we use it as default setting
* otherwise we take the number of available processors, retrieved by `Runtime.getRuntime().availableProcessors()` _(which, as a well-known fact, sometimes does not represent the actual number of processors)_
* in any case if the chosen number is lower than the minimum, which is `2` threads, then we use the minimum.

### Advanced settings

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12 changes: 5 additions & 7 deletions src/main/java/io/lettuce/core/AbstractRedisClient.java
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Expand Up @@ -60,28 +60,26 @@
import io.netty.channel.EventLoopGroup;
import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.util.concurrent.EventExecutorGroup;
import io.netty.util.concurrent.Future;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

/**
* Base Redis client. This class holds the netty infrastructure, {@link ClientOptions} and the basic connection procedure. This
* class creates the netty {@link EventLoopGroup}s for NIO ({@link NioEventLoopGroup}) and EPoll (
* {@link io.netty.channel.epoll.EpollEventLoopGroup}) with a default of {@code Runtime.getRuntime().availableProcessors() * 4}
* threads. Reuse the instance as much as possible since the {@link EventLoopGroup} instances are expensive and can consume a
* huge part of your resources, if you create multiple instances.
* class creates different Netty {@link EventLoopGroup}s depending on the {@link NativeTransports} used.
* <p>
* You can set the number of threads per {@link NioEventLoopGroup} by setting the {@code io.netty.eventLoopThreads} system
* property to a reasonable number of threads.
* You can set the number of threads by using the {@link ClientResources} configuration. For more details, check the
* documentation of the {@link DefaultClientResources} class.
* </p>
*
* @author Mark Paluch
* @author Jongyeol Choi
* @author Poorva Gokhale
* @author Tihomir Mateev
* @since 3.0
* @see ClientResources
* @see DefaultClientResources
*/
public abstract class AbstractRedisClient implements AutoCloseable {

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