我们目前使用的是低于log4j的jar
log4j-core-2.6.2、log4j-flume-ng-2.6.2

<Flume name="aggregatorApp" compress="false" type="Avro"
ignoreExceptions="true" batchSize="10" blocking="false" >
<Agent host="${flumeHostPrimary}" port="${flumePortPrimary}" />
<Agent host="${flumeHostSecondary}" port="${flumePortSecondary}" />
<FlumeEventFactory logType="APPLICATION"/>
<PatternLayout header="app" pattern="[%-5p] %d %c %X{correlationId} - %m" />

<AsyncLogger name="com.xyz.abc" level="debug"
additivity="false" blocking="false">
<AppenderRef ref="IDRESTSERVICELOG" />
<AppenderRef ref="aggregatorApp" level="INFO" />
<AppenderRef ref="CONSOLE" level="INFO"/>
</AsyncLogger>

当flume代理启动并运行时，应用程序运行平稳，日志事件成功发布到flume代理
如果flume代理停止运行一段时间，应用程序线程就会出现以下异常
 

Exception in thread "elasticsearch[_client_][generic][T#3]" java.lang.OutOfMemoryError: GC overhead limit exceeded
2019-02-01 07:43:23,618 [ContainerBackgroundProcessor[StandardEngine[Catalina]]] WARN  org.apache.catalina.valves.StuckThreadDetectionValve- Thread "http-apr-8080-exec-7" (id=167) has been active for 20,392 milliseconds (since 2/1/19 7:42 AM) to serve the same request for htpps://xyz//directories/v1.0/search and may be stuck (configured threshold for this StuckThreadDetectionValve is 20 seconds). There is/are 1 thread(s) in total that are monitored by this Valve and may be stuck.
2019-02-01 07:46:18,619 [ContainerBackgroundProcessor[StandardEngine[Catalina]]] ERROR org.apache.catalina.core.ContainerBase- Unexpected death of background thread ContainerBackgroundProcessor[StandardEngine[Catalina]]
java.lang.OutOfMemoryError: GC overhead limit exceeded
Exception in thread "http-apr-8080-exec-42" java.lang.OutOfMemoryError: GC overhead limit exceeded
Exception in thread "http-apr-8080-exec-50" Exception in thread "ContainerBackgroundProcessor[StandardEngine[Catalina]]" Exception in thread "I/O dispatcher 23" 
Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "ContainerBackgroundProcessor[StandardEngine[Catalina]]"
Exception in thread "http-apr-8080-exec-38" Exception in thread "http-apr-8080-exec-46" Exception in thread "http-apr-8080-exec-53" Exception in thread "I/O dispatcher 17" 
Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "http-apr-8080-exec-31"

以上异常在重载期间发生（每个请求记录1mb日志）注意：我们正在进行负载测试
由于应用程序日志记录量很大，但flume appender不能以同样的速度使用。我们怀疑log4j环缓冲区已满，这会阻塞应用程序线程并产生内存不足异常。
考虑到log4j appenders有问题，我们尝试了几次行动，
-dlog4j2.asyncqueuefullpolicy=discard-dlog4j2.enable.threadlocals=true-dlog4j2.enable.direct.encoders=true
但上述系统属性没有任何用处。我们错过什么了吗？