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From kayousterhout <...@git.apache.org>
Subject [GitHub] spark pull request #14079: [SPARK-8425][CORE] Application Level Blacklisting
Date Tue, 13 Dec 2016 06:23:24 GMT
Github user kayousterhout commented on a diff in the pull request:

    https://github.com/apache/spark/pull/14079#discussion_r92076298
  
    --- Diff: core/src/main/scala/org/apache/spark/scheduler/BlacklistTracker.scala ---
    @@ -17,10 +17,275 @@
     
     package org.apache.spark.scheduler
     
    +import java.util.concurrent.atomic.AtomicReference
    +
    +import scala.collection.mutable.{ArrayBuffer, HashMap, HashSet}
    +
     import org.apache.spark.SparkConf
     import org.apache.spark.internal.Logging
     import org.apache.spark.internal.config
    -import org.apache.spark.util.Utils
    +import org.apache.spark.util.{Clock, SystemClock, Utils}
    +
    +/**
    + * BlacklistTracker is designed to track problematic executors and nodes.  It supports
blacklisting
    + * executors and nodes across an entire application (with a periodic expiry).  TaskSetManagers
add
    + * additional blacklisting of executors and nodes for individual tasks and stages which
works in
    + * concert with the blacklisting here.
    + *
    + * The tracker needs to deal with a variety of workloads, eg.:
    + *
    + *  * bad user code --  this may lead to many task failures, but that should not count
against
    + *      individual executors
    + *  * many small stages -- this may prevent a bad executor for having many failures within
one
    + *      stage, but still many failures over the entire application
    + *  * "flaky" executors -- they don't fail every task, but are still faulty enough to
merit
    + *      blacklisting
    + *
    + * See the design doc on SPARK-8425 for a more in-depth discussion.
    + *
    + * THREADING: As with most helpers of TaskSchedulerImpl, this is not thread-safe.  Though
it is
    + * called by multiple threads, callers must already have a lock on the TaskSchedulerImpl.
 The
    + * one exception is [[nodeBlacklist()]], which can be called without holding a lock.
    + */
    +private[scheduler] class BlacklistTracker (
    +    conf: SparkConf,
    +    clock: Clock = new SystemClock()) extends Logging {
    +
    +  BlacklistTracker.validateBlacklistConfs(conf)
    +  private val MAX_FAILURES_PER_EXEC = conf.get(config.MAX_FAILURES_PER_EXEC)
    +  private val MAX_FAILED_EXEC_PER_NODE = conf.get(config.MAX_FAILED_EXEC_PER_NODE)
    +  val BLACKLIST_TIMEOUT_MILLIS = BlacklistTracker.getBlacklistTimeout(conf)
    +
    +  /**
    +   * A map from executorId to information on task failures.  Tracks the time of each
task failure,
    +   * so that we can avoid blacklisting executors due to failures that are very far apart.
 We do not
    +   * actively remove from this as soon as tasks hit their timeouts, to avoid the time
it would take
    +   * to do so.  But it will not grow too large, because as soon as an executor gets too
many
    +   * failures, we blacklist the executor and remove its entry here.
    +   */
    +  private val executorIdToFailureList = new  HashMap[String, ExecutorFailureList]()
    +  val executorIdToBlacklistStatus = new HashMap[String, BlacklistedExecutor]()
    +  val nodeIdToBlacklistExpiryTime = new HashMap[String, Long]()
    +  /**
    +   * An immutable copy of the set of nodes that are currently blacklisted.  Kept in an
    +   * AtomicReference to make [[nodeBlacklist()]] thread-safe.
    +   */
    +  private val _nodeBlacklist = new AtomicReference[Set[String]](Set())
    +  /**
    +   * Time when the next blacklist will expire.  Used as a
    +   * shortcut to avoid iterating over all entries in the blacklist when none will have
expired.
    +   */
    +  var nextExpiryTime: Long = Long.MaxValue
    +  /**
    +   * Mapping from nodes to all of the executors that have been blacklisted on that node.
We do *not*
    +   * remove from this when executors are removed from spark, so we can track when we
get multiple
    +   * successive blacklisted executors on one node.  Nonetheless, it will not grow too
large because
    +   * there cannot be many blacklisted executors on one node, before we stop requesting
more
    +   * executors on that node, and we clean up the list of blacklisted executors once an
executor has
    +   * been blacklisted for BLACKLIST_TIMEOUT_MILLIS.
    +   */
    +  val nodeToBlacklistedExecs = new HashMap[String, HashSet[String]]()
    +
    +  /**
    +   * Un-blacklists executors and nodes that have been blacklisted for at least
    +   * BLACKLIST_TIMEOUT_MILLIS
    +   */
    +  def applyBlacklistTimeout(): Unit = {
    +    val now = clock.getTimeMillis()
    +    // quickly check if we've got anything to expire from blacklist -- if not, avoid
doing any work
    +    if (now > nextExpiryTime) {
    +      // Apply the timeout to blacklisted nodes and executors
    +      val execsToUnblacklist = executorIdToBlacklistStatus.filter(_._2.expiryTime <
now).keys
    +      if (execsToUnblacklist.nonEmpty) {
    +        // Un-blacklist any executors that have been blacklisted longer than the blacklist
timeout.
    +        logInfo(s"Removing executors $execsToUnblacklist from blacklist because the blacklist
" +
    +          s"for those executors has timed out")
    +        execsToUnblacklist.foreach { exec =>
    +          val status = executorIdToBlacklistStatus.remove(exec).get
    +          val failedExecsOnNode = nodeToBlacklistedExecs(status.node)
    +          failedExecsOnNode.remove(exec)
    +          if (failedExecsOnNode.isEmpty) {
    +            nodeToBlacklistedExecs.remove(status.node)
    +          }
    +        }
    +      }
    +      val nodesToUnblacklist = nodeIdToBlacklistExpiryTime.filter(_._2 < now).keys
    +      if (nodesToUnblacklist.nonEmpty) {
    +        // Un-blacklist any nodes that have been blacklisted longer than the blacklist
timeout.
    +        logInfo(s"Removing nodes $nodesToUnblacklist from blacklist because the blacklist
" +
    +          s"has timed out")
    +        nodeIdToBlacklistExpiryTime --= nodesToUnblacklist
    +        _nodeBlacklist.set(nodeIdToBlacklistExpiryTime.keySet.toSet)
    +      }
    +      updateNextExpiryTime()
    +    }
    +  }
    +
    +  private def updateNextExpiryTime(): Unit = {
    +    val execMinExpiry = if (executorIdToBlacklistStatus.nonEmpty) {
    +      executorIdToBlacklistStatus.map{_._2.expiryTime}.min
    +    } else {
    +      Long.MaxValue
    +    }
    +    val nodeMinExpiry = if (nodeIdToBlacklistExpiryTime.nonEmpty) {
    +      nodeIdToBlacklistExpiryTime.values.min
    +    } else {
    +      Long.MaxValue
    +    }
    +    nextExpiryTime = math.min(execMinExpiry, nodeMinExpiry)
    +  }
    +
    +
    +  def updateBlacklistForSuccessfulTaskSet(
    +      stageId: Int,
    +      stageAttemptId: Int,
    +      failuresByExec: HashMap[String, ExecutorFailuresInTaskSet]): Unit = {
    +    // if any tasks failed, we count them towards the overall failure count for the executor
at
    +    // this point.
    +    val now = clock.getTimeMillis()
    +    val expiryTime = now + BLACKLIST_TIMEOUT_MILLIS
    +    failuresByExec.foreach { case (exec, failuresInTaskSet) =>
    +      val allFailuresOnOneExecutor =
    +        executorIdToFailureList.getOrElseUpdate(exec, new ExecutorFailureList)
    +      allFailuresOnOneExecutor.dropFailuresWithTimeoutBefore(now)
    +      allFailuresOnOneExecutor.addFailures(stageId, stageAttemptId, failuresInTaskSet)
    +      val newTotal = allFailuresOnOneExecutor.numUniqueTaskFailures
    +
    +      // If this pushes the total number of failures over the threshold, blacklist the
executor.
    +      // If its already blacklisted, we avoid "re-blacklisting" (which can happen if
there were
    +      // other tasks already running in another taskset when it got blacklisted), because
it makes
    +      // some of the logic around expiry times a little more confusing.  But it also
wouldn't be a
    +      // problem to re-blacklist, with a later expiry time.
    +      if (newTotal >= MAX_FAILURES_PER_EXEC && !executorIdToBlacklistStatus.contains(exec))
{
    +        logInfo(s"Blacklisting executor id: $exec because it has $newTotal" +
    +          s" task failures in successful task sets")
    +        val node = failuresInTaskSet.node
    +        executorIdToBlacklistStatus.put(exec, BlacklistedExecutor(node, expiryTime))
    +        updateNextExpiryTime()
    +
    +        // In addition to blacklisting the executor, we also update the data for failures
on the
    +        // node, and potentially put the entire node into a blacklist as well.
    +        val blacklistedExecsOnNode = nodeToBlacklistedExecs.getOrElseUpdate(node, HashSet[String]())
    +        blacklistedExecsOnNode += exec
    +        // If the node is already in the blacklist, we avoid adding it again with a later
expiry
    +        // time.
    +        if (blacklistedExecsOnNode.size >= MAX_FAILED_EXEC_PER_NODE &&
    +            !nodeIdToBlacklistExpiryTime.contains(node)) {
    +          logInfo(s"Blacklisting node $node because it has ${blacklistedExecsOnNode.size}
" +
    +            s"executors blacklisted: ${blacklistedExecsOnNode}")
    +          nodeIdToBlacklistExpiryTime.put(node, expiryTime)
    +          _nodeBlacklist.set(nodeIdToBlacklistExpiryTime.keySet.toSet)
    +        }
    +      }
    +    }
    +  }
    +
    +  def isExecutorBlacklisted(executorId: String): Boolean = {
    +    executorIdToBlacklistStatus.contains(executorId)
    +  }
    +
    +  /**
    +   * Get the full set of nodes that are blacklisted.  Unlike other methods in this class,
this *IS*
    +   * thread-safe -- no lock required on a taskScheduler.
    +   */
    +  def nodeBlacklist(): Set[String] = {
    +    _nodeBlacklist.get()
    +  }
    +
    +  def isNodeBlacklisted(node: String): Boolean = {
    +    nodeIdToBlacklistExpiryTime.contains(node)
    +  }
    +
    +  def handleRemovedExecutor(executorId: String): Unit = {
    +    // We intentionally do not clean up executors that are already blacklisted in
    +    // nodeToBlacklistedExecs, so that if another executor on the same node gets blacklisted,
we can
    +    // blacklist the entire node.  We also can't clean up executorIdToBlacklistStatus,
so we can
    +    // eventually remove the executor after the timeout.  Despite not clearing those
structures
    +    // here, we don't expect they will grow too big since you won't get too many executors
on one
    +    // node, and the timeout will clear it up periodically in any case.
    +    executorIdToFailureList -= executorId
    +  }
    +
    +
    +  /**
    +   * Tracks all failures for one executor (that have not passed the timeout).  Designed
to
    +   * efficiently remove failures that are older than the timeout, and query for the number
of unique
    --- End diff --
    
    I think the "Designed to efficiently..." part of this comment is old and from when there
were more optimized data structures below? (so just remove it)


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