Quarkus BackPressure配置

Question

我使用quarkus smallrye reactive messaging和kafka获得了以下堆栈跟踪：

2020-07-24 01:38:31,662 ERROR [io.sma.rea.mes.kafka] (executor-thread-870) SRMSG18207: Unable to dispatch message to Kafka: io.smallrye.mutiny.subscription.BackPressureFailure: Could not emit tick 211 due to lack of requests
        at io.smallrye.mutiny.operators.multi.builders.IntervalMulti$IntervalRunnable.run(IntervalMulti.java:83)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
        at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:2046)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1578)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1452)
        at org.jboss.threads.DelegatingRunnable.run(DelegatingRunnable.java:29)
        at org.jboss.threads.ThreadLocalResettingRunnable.run(ThreadLocalResettingRunnable.java:29)
        at java.lang.Thread.run(Thread.java:748)
        at org.jboss.threads.JBossThread.run(JBossThread.java:479)

因此，我已经阅读了https://smallrye.io/smallrye-mutiny/#_how_do_i_control_the_back_pressure。

根据文档，我添加了BackPressure控件。

之前：

@Outgoing( "eqs-crossing-xxx" )
    public Multi< EQSAlert > eqsCrossingXXX_XXX(){

        final String series = CrossingEnum.XXX_XXX.getSeries();
        final String equipment = CrossingEnum.XXX_XXX.getEquipment();

        final String vehicleRegex = vehicleRegexService.getRegexBySeries( series );

        log.info( "Incoming request for {} - {}",  series, equipment);
        log.info( "Vehicle regex : {}", vehicleRegex );

        return Multi
                .createFrom()
                .ticks()
                .every(
                        Duration.ofSeconds( poolingInterval )
                )
                .concatMap(i -> {
                    final Multi<CrossingState> crossingStateBySeriesAndEquipment = CrossingState.getCrossingStateBySeriesAndEquipment(client, series, equipment);

                    return crossingStateBySeriesAndEquipment.flatMap(crossingState ->
                            crossingState.isActive() ?
                                    EQSAlert.getEQSAlertBySeriesAndEquipment(
                                            client,
                                            series,
                                            vehicleRegex,
                                            equipment
                                    )
                                    :
                                    Multi.createFrom().empty()
                    );
                });
    }

之后：

@Outgoing( "eqs-crossing-xxx" )
    public Multi< EQSAlert > eqsCrossingXXX_XXX(){

        final String series = CrossingEnum.XXX_XXX.getSeries();
        final String equipment = CrossingEnum.XXX_XXX.getEquipment();

        final String vehicleRegex = vehicleRegexService.getRegexBySeries( series );

        log.info( "Incoming request for {} - {}",  series, equipment);
        log.info( "Vehicle regex : {}", vehicleRegex );

        return Multi
                .createFrom()
                .ticks()
                .every(
                        Duration.ofSeconds( poolingInterval )
                )
                .onOverflow()
                .buffer(10)
                .concatMap(i -> {
                    final Multi<CrossingState> crossingStateBySeriesAndEquipment = CrossingState.getCrossingStateBySeriesAndEquipment(client, series, equipment);

                    return crossingStateBySeriesAndEquipment.flatMap(crossingState ->
                            crossingState.isActive() ?
                                    EQSAlert.getEQSAlertBySeriesAndEquipment(
                                            client,
                                            series,
                                            vehicleRegex,
                                            equipment
                                    )
                                    :
                                    Multi.createFrom().empty()
                    );
                });
    }

现在一切都好了。

我这篇文章的目的是为了理解为什么我需要这样做？

https://smallrye.io/smallrye-mutiny/apidocs/io/smallrye/mutiny/subscription/BackPressureStrategy.html

为什么缓冲区不能容纳你？

如您所见，我每隔5秒执行一次简单的sql函数调用(poolingInterval)。该函数返回一些记录(通过池化决不会超过10条)

所以交通量非常低

我可以说几句话来理解缓冲区管理吗？

谢谢

Answer 1

您的下游每单位时间只能消耗一定数量的项目。这取决于你在做什么。默认情况下，Kafka限制为5个并发写入(您可以配置)。

因此，如果你排放更多，以一种无界的-没有反压力感知-的方式，下游无法跟上。添加10个项目的缓冲区可能会处理小的凹凸，但这可能还不够。

drop更激进；如果下游跟不上，这些项目就会被简单地丢弃。dropPreviousItems正在丢弃已收到的项目。