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How To Set Event-loop Pool Size In Spring Webflux / WebClient?

In multi-reactor framework such as Vert.X we can set the number of event-loop threads, e.g.:

final VertxOptions vertxOptions = new VertxOptions();
vertxOptions.setEventLoopPoolSize(16);
final Vertx myVertx = Vertx.vertx(vertxOptions);

How to do the equivalent in Spring Boot 2 WebFlux / WebClient?

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Answer

You have two options:

  1. Override ReactiveWebServerFactory bean with a customizer that applies event loop resources config:

    @Bean
    public ReactiveWebServerFactory reactiveWebServerFactory() {
        NettyReactiveWebServerFactory factory = new NettyReactiveWebServerFactory();
        factory.addServerCustomizers(builder -> builder.loopResources(LoopResources.create("my-http", 16, true)));
    
        return factory;
    }
    
  2. Or use -Dreactor.ipc.netty.workerCount=16 environment variable. By default it's value is set to Math.max(availableProcessors(), 4). Example: java -jar your-app.jar -Dreactor.ipc.netty.workerCount=16

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source: stackoverflow.com
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