spark通過kafka-appender指定日志輸出到kafka引發(fā)的死鎖問題

更新時間：2020年05月08日 11:15:35 作者：民工哥

這篇文章主要介紹了spark通過kafka-appender指定日志輸出到kafka引發(fā)的死鎖，本文通過實例代碼給大家介紹的非常詳細，對大家的學習或工作具有一定的參考借鑒價值,需要的朋友可以參考下

在采用log4j的kafka-appender收集spark任務運行日志時，發(fā)現(xiàn)提交到yarn上的任務始終ACCEPTED狀態(tài)，無法進入RUNNING狀態(tài)，并且會重試兩次后超時。期初認為是yarn資源不足導致，但在確認yarn資源充裕的時候問題依舊，而且基本上能穩(wěn)定復現(xiàn)。

起初是這么配置spark日志輸出到kafka的：

log4j.rootCategory=INFO, console, kafka
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.target=System.err
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%d{yyyy/MM/dd HH:mm:ss.SSS} %p %c{1}: [${log4j.pipelineId}] %m%n

# Kafka appender
log4j.appender.kafka=org.apache.kafka.log4jappender.KafkaLog4jAppender
# Set Kafka topic and brokerList
log4j.appender.kafka.topic=yarn_spark_log
log4j.appender.kafka.brokerList=localhost:9092
log4j.appender.kafka.compressionType=none
log4j.appender.kafka.syncSend=false
log4j.appender.kafka.maxBlockMs=10
log4j.appender.kafka.layout=org.apache.log4j.PatternLayout
log4j.appender.kafka.layout.ConversionPattern=%d{yyyy/MM/dd HH:mm:ss.SSS} %p %c{1}: [${log4j.pipelineId}] %m

這里用org.apache.kafka.log4jappender.KafkaLog4jAppender默認將所有日志都輸出到kafka，這個appender已經(jīng)被kafka官方維護，穩(wěn)定性應該是可以保障的。

問題定位

發(fā)現(xiàn)問題后，嘗試將輸出到kafka的規(guī)則去掉，問題解除！于是把問題定位到跟日志輸出到kafka有關。通過其他測試，證實目標kafka其實是正常的，這就非常奇怪了。

查看yarn的ResourceManager日志，發(fā)現(xiàn)有如下超時

2020-05-07 21:49:48,230 INFO org.apache.hadoop.yarn.util.AbstractLivelinessMonitor: Expired:appattempt_1578970174552_3204_000002 Timed out after 600 secs
2020-05-07 21:49:48,230 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl: Updating application attempt appattempt_1578970174552_3204_000002 with final
state: FAILED, and exit status: -1000
2020-05-07 21:49:48,231 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl: appattempt_1578970174552_3204_000002 State change from LAUNCHED to FINAL_SAV
ING on event = EXPIRE

表明，yarn本身是接收任務的，但是發(fā)現(xiàn)任務遲遲沒有啟動。在spark的場景下其實是指只有driver啟動了，但是沒有啟動executor。
而查看driver日志，發(fā)現(xiàn)日志輸出到一個地方就卡住了，不往下繼續(xù)了。通過對比成功運行和卡住的情況發(fā)現(xiàn)，日志卡在這條上：

2020/05/07 19:37:10.324 INFO SecurityManager: Changing view acls to: yarn,root
2020/05/07 19:37:10.344 INFO Metadata: Cluster ID: 6iG6WHA2SoK7FfgGgWHt_A

卡住的情況下，只會打出SecurityManager這行，而無法打出Metadata這行。
猜想Metadata這行是kafka-client本身打出來的，因為整個上下文只有yarn, spark, kafka-client可能會打出這個日志。

在kafka-client 2.2.0版本中找到這個日志是輸出位置：

public synchronized void update(MetadataResponse metadataResponse, long now) {
  ...

  String newClusterId = cache.cluster().clusterResource().clusterId();
  if (!Objects.equals(previousClusterId, newClusterId)) {
    log.info("Cluster ID: {}", newClusterId);
  }
  ...
}

看到synchronized，高度懷疑死鎖。于是考慮用jstack分析：

在yarn上運行spark任務的時候，driver進程叫ApplicationMaster，executor進程叫CoarseGrainedExecutorBackend。這里首先嘗試再復現(xiàn)過程中找到drvier最終在哪個節(jié)點上運行，然后快速使用jstack -F <pid>打印堆棧

jstack果然不負眾望，報告了死鎖！這里我把結(jié)果貼的全一點

[root@node1 ~]# jstack 20136
20136: Unable to open socket file: target process not responding or HotSpot VM not loaded
The -F option can be used when the target process is not responding
[root@node1 ~]# jstack -F 20136
Attaching to process ID 20136, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.231-b11
Deadlock Detection:

Found one Java-level deadlock:
=============================

"kafka-producer-network-thread | producer-1":
 waiting to lock Monitor@0x00000000025fcc48 (Object@0x00000000ed680b60, a org/apache/kafka/log4jappender/KafkaLog4jAppender),
 which is held by "main"
"main":
 waiting to lock Monitor@0x00007fec9dbde038 (Object@0x00000000ee44de38, a org/apache/kafka/clients/Metadata),
 which is held by "kafka-producer-network-thread | producer-1"

Found a total of 1 deadlock.

Thread 20157: (state = BLOCKED)
 - org.apache.log4j.AppenderSkeleton.doAppend(org.apache.log4j.spi.LoggingEvent) @bci=0, line=231 (Interpreted frame)
 - org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(org.apache.log4j.spi.LoggingEvent) @bci=41, line=66 (Interpreted frame)
 - org.apache.log4j.Category.callAppenders(org.apache.log4j.spi.LoggingEvent) @bci=26, line=206 (Interpreted frame)
 - org.apache.log4j.Category.forcedLog(java.lang.String, org.apache.log4j.Priority, java.lang.Object, java.lang.Throwable) @bci=14, line=391 (Interpreted frame)
 - org.apache.log4j.Category.log(java.lang.String, org.apache.log4j.Priority, java.lang.Object, java.lang.Throwable) @bci=34, line=856 (Interpreted frame)
 - org.slf4j.impl.Log4jLoggerAdapter.info(java.lang.String, java.lang.Object) @bci=34, line=324 (Interpreted frame)
 - org.apache.kafka.clients.Metadata.update(org.apache.kafka.common.requests.MetadataResponse, long) @bci=317, line=365 (Interpreted frame)
 - org.apache.kafka.clients.NetworkClient$DefaultMetadataUpdater.handleCompletedMetadataResponse(org.apache.kafka.common.requests.RequestHeader, long, org.apache.kafka.common.requests.MetadataResponse) @bci=184, line=1031 (Interpreted frame)
 - org.apache.kafka.clients.NetworkClient.handleCompletedReceives(java.util.List, long) @bci=215, line=822 (Interpreted frame)
 - org.apache.kafka.clients.NetworkClient.poll(long, long) @bci=132, line=544 (Interpreted frame)
 - org.apache.kafka.clients.producer.internals.Sender.run(long) @bci=227, line=311 (Interpreted frame)
 - org.apache.kafka.clients.producer.internals.Sender.run() @bci=28, line=235 (Interpreted frame)
 - java.lang.Thread.run() @bci=11, line=748 (Interpreted frame)


Thread 20150: (state = BLOCKED)


Thread 20149: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - java.lang.ref.ReferenceQueue.remove(long) @bci=59, line=144 (Interpreted frame)
 - java.lang.ref.ReferenceQueue.remove() @bci=2, line=165 (Interpreted frame)
 - java.lang.ref.Finalizer$FinalizerThread.run() @bci=36, line=216 (Interpreted frame)


Thread 20148: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - java.lang.Object.wait() @bci=2, line=502 (Interpreted frame)
 - java.lang.ref.Reference.tryHandlePending(boolean) @bci=54, line=191 (Interpreted frame)
 - java.lang.ref.Reference$ReferenceHandler.run() @bci=1, line=153 (Interpreted frame)


Thread 20137: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - org.apache.kafka.clients.Metadata.awaitUpdate(int, long) @bci=63, line=261 (Interpreted frame)
 - org.apache.kafka.clients.producer.KafkaProducer.waitOnMetadata(java.lang.String, java.lang.Integer, long) @bci=160, line=983 (Interpreted frame)
 - org.apache.kafka.clients.producer.KafkaProducer.doSend(org.apache.kafka.clients.producer.ProducerRecord, org.apache.kafka.clients.producer.Callback) @bci=19, line=860 (Interpreted frame)
 - org.apache.kafka.clients.producer.KafkaProducer.send(org.apache.kafka.clients.producer.ProducerRecord, org.apache.kafka.clients.producer.Callback) @bci=12, line=840 (Interpreted frame)
 - org.apache.kafka.clients.producer.KafkaProducer.send(org.apache.kafka.clients.producer.ProducerRecord) @bci=3, line=727 (Interpreted frame)
 - org.apache.kafka.log4jappender.KafkaLog4jAppender.append(org.apache.log4j.spi.LoggingEvent) @bci=69, line=283 (Interpreted frame)
 - org.apache.log4j.AppenderSkeleton.doAppend(org.apache.log4j.spi.LoggingEvent) @bci=106, line=251 (Interpreted frame)
 - org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(org.apache.log4j.spi.LoggingEvent) @bci=41, line=66 (Interpreted frame)
 - org.apache.log4j.Category.callAppenders(org.apache.log4j.spi.LoggingEvent) @bci=26, line=206 (Interpreted frame)
 - org.apache.log4j.Category.forcedLog(java.lang.String, org.apache.log4j.Priority, java.lang.Object, java.lang.Throwable) @bci=14, line=391 (Interpreted frame)
 - org.apache.log4j.Category.log(java.lang.String, org.apache.log4j.Priority, java.lang.Object, java.lang.Throwable) @bci=34, line=856 (Interpreted frame)
 - org.slf4j.impl.Log4jLoggerAdapter.info(java.lang.String) @bci=12, line=305 (Interpreted frame)
 - org.apache.spark.internal.Logging$class.logInfo(org.apache.spark.internal.Logging, scala.Function0) @bci=29, line=54 (Interpreted frame)
 - org.apache.spark.SecurityManager.logInfo(scala.Function0) @bci=2, line=44 (Interpreted frame)
 - org.apache.spark.SecurityManager.setViewAcls(scala.collection.immutable.Set, java.lang.String) @bci=36, line=139 (Interpreted frame)
 - org.apache.spark.SecurityManager.<init>(org.apache.spark.SparkConf, scala.Option) @bci=158, line=81 (Interpreted frame)
 - org.apache.spark.deploy.yarn.ApplicationMaster.<init>(org.apache.spark.deploy.yarn.ApplicationMasterArguments) @bci=85, line=70 (Interpreted frame)
 - org.apache.spark.deploy.yarn.ApplicationMaster$.main(java.lang.String[]) @bci=25, line=802 (Interpreted frame)
 - org.apache.spark.deploy.yarn.ApplicationMaster.main(java.lang.String[]) @bci=4 (Interpreted frame)

到這里，已經(jīng)確定是死鎖，導致driver一開始就運行停滯，那么當然無法提交executor執(zhí)行。
具體的死鎖稍后分析，先考慮如何解決。從感性認識看，似乎只要不讓kafka-client的日志也輸出到kafka即可。實驗后，發(fā)現(xiàn)果然如此：如果只輸出org.apache.spark的日志就可以正常執(zhí)行。

根因分析

從stack的結(jié)果看，造成死鎖的是如下兩個線程：

kafka-client內(nèi)部的網(wǎng)絡線程spark
主入口線程

兩個線程其實都是卡在打日志上了，觀察堆?？梢园l(fā)現(xiàn)，兩個線程同時持有了同一個log對象。而這個log對象實際上是kafka-appender。而kafka-appender本質(zhì)上持有kafka-client，及其內(nèi)部的Metadata對象。log4j的doAppend為了保證線程安全也用synchronized修飾了：

public
 synchronized 
 void doAppend(LoggingEvent event) {
  if(closed) {
   LogLog.error("Attempted to append to closed appender named ["+name+"].");
   return;
  }
  
  if(!isAsSevereAsThreshold(event.level)) {
   return;
  }

  Filter f = this.headFilter;
  
  FILTER_LOOP:
  while(f != null) {
   switch(f.decide(event)) {
   case Filter.DENY: return;
   case Filter.ACCEPT: break FILTER_LOOP;
   case Filter.NEUTRAL: f = f.next;
   }
  }
  
  this.append(event);  
 }

于是事情開始了：

main線程嘗試打日志，首先進入了synchronized的doAppend，即獲取了kafka-appender的鎖
kafka-appender內(nèi)部需要調(diào)用kafka-client發(fā)送日志到kafka，最終調(diào)用到Thread 20137展示的，運行到Metadata.awaitUpdate（也是個synchronized方法），內(nèi)部的wait會嘗試獲取metadata的鎖。（詳見https://github.com/apache/kaf...）
但此時，kafka-producer-network-thread線程剛好進入了上文提到的打Cluster ID這個日志的這個階段（update方法也是synchronized的），也就是說kafka-producer-network-thread線程獲得了metadata對象的鎖
kafka-producer-network-thread線程要打印日志同樣執(zhí)行synchronized的doAppend，即獲取了kafka-appender的鎖