More logging around rebalancing when rebalanceSafeCommits is true (#1360)

Follow up of #1358 

See also #1132

---------

Co-authored-by: Erik van Oosten <[email protected]>

Author: svroonland

zio-kafka-test/src/test/scala/zio/kafka/consumer/ConsumerSpec.scala

@@ -769,7 +769,8 @@ object ConsumerSpec extends ZIOSpecDefaultSlf4j with KafkaRandom {
                               clientId = clientId,
                               groupId = Some(groupId),
                               `max.poll.records` = 1,
-                              rebalanceSafeCommits = rebalanceSafeCommits
+                              rebalanceSafeCommits = rebalanceSafeCommits,
+                              maxRebalanceDuration = 60.seconds
                             )
                 consumer <- Consumer.make(settings)
               } yield consumer

zio-kafka/src/main/scala/zio/kafka/consumer/internal/Runloop.scala

@@ -111,6 +111,8 @@ private[consumer] final class Runloop private (
     ): Task[Unit] = {
       val deadline = java.lang.System.nanoTime() + maxRebalanceDuration.toNanos - commitTimeoutNanos
 
+      def timeToDeadlineMillis(): Long = (deadline - java.lang.System.nanoTime()) / 1000000L
+
       val endingTps = streamsToEnd.map(_.tp).toSet
 
       def commitsOfEndingStreams(commits: Chunk[Runloop.Commit]): Chunk[Runloop.Commit] =
@@ -130,36 +132,92 @@ private[consumer] final class Runloop private (
           ZIO.attempt(consumer.commitAsync(java.util.Collections.emptyMap(), null)).orDie
         }
 
-      def endingStreamsCompletedAndCommitsExist(newCommits: Chunk[Commit]): Task[Boolean] =
+      sealed trait EndOffsetCommitStatus
+      case object EndOffsetNotCommitted  extends EndOffsetCommitStatus { override def toString = "not committed"  }
+      case object EndOffsetCommitPending extends EndOffsetCommitStatus { override def toString = "commit pending" }
+      case object EndOffsetCommitted     extends EndOffsetCommitStatus { override def toString = "committed"      }
+
+      final case class StreamCompletionStatus(
+        tp: TopicPartition,
+        streamEnded: Boolean,
+        lastPulledOffset: Option[Long],
+        endOffsetCommitStatus: EndOffsetCommitStatus
+      ) {
+        override def toString: String =
+          s"${tp}: " +
+            s"${if (streamEnded) "stream ended" else "stream is running"}, " +
+            s"last pulled offset=${lastPulledOffset.getOrElse("none")}, " +
+            endOffsetCommitStatus
+      }
+
+      def completionStatusesAsString(completionStatuses: Chunk[StreamCompletionStatus]): String =
+        "Revoked partitions: " + completionStatuses.map(_.toString).mkString("; ")
+
+      def getStreamCompletionStatuses(newCommits: Chunk[Commit]): UIO[Chunk[StreamCompletionStatus]] =
         for {
+          committedOffsets <- committedOffsetsRef.get
+          allPendingCommitOffsets =
+            (previousPendingCommits ++ commitsOfEndingStreams(newCommits)).flatMap(_.offsets).map {
+              case (tp, offsetAndMetadata) => (tp, offsetAndMetadata.offset())
+            }
           streamResults <-
             ZIO.foreach(streamsToEnd) { stream =>
               for {
                 isDone           <- stream.completedPromise.isDone
                 lastPulledOffset <- stream.lastPulledOffset
                 endOffset        <- if (isDone) stream.completedPromise.await else ZIO.none
-              } yield (isDone || lastPulledOffset.isEmpty, endOffset)
-            }
-          committedOffsets <- committedOffsetsRef.get
-        } yield {
-          val allStreamsCompleted = streamResults.forall(_._1)
-          allStreamsCompleted && {
-            val endOffsets: Chunk[Offset] = streamResults.flatMap(_._2)
-            val allPendingCommits         = previousPendingCommits ++ commitsOfEndingStreams(newCommits)
-            endOffsets.forall { endOffset =>
-              val tp                    = endOffset.topicPartition
-              val offset                = endOffset.offset
-              def endOffsetWasCommitted = committedOffsets.contains(tp, offset)
-              def endOffsetCommitIsPending = allPendingCommits.exists { pendingCommit =>
-                pendingCommit.offsets.get(tp).exists { pendingOffset =>
-                  pendingOffset.offset() >= offset
-                }
-              }
-              endOffsetWasCommitted || endOffsetCommitIsPending
+
+                endOffsetCommitStatus =
+                  endOffset match {
+                    case Some(endOffset) if committedOffsets.contains(stream.tp, endOffset.offset) =>
+                      EndOffsetCommitted
+                    case Some(endOffset) if allPendingCommitOffsets.contains((stream.tp, endOffset.offset)) =>
+                      EndOffsetCommitPending
+                    case _ => EndOffsetNotCommitted
+                  }
+              } yield StreamCompletionStatus(stream.tp, isDone, lastPulledOffset.map(_.offset), endOffsetCommitStatus)
             }
-          }
+        } yield streamResults
+
+      @inline
+      def logStreamCompletionStatuses(completionStatuses: Chunk[StreamCompletionStatus]): UIO[Unit] = {
+        val statusStrings = completionStatusesAsString(completionStatuses)
+        ZIO.logInfo(
+          s"Delaying rebalance until ${streamsToEnd.size} streams (of revoked partitions) have committed " +
+            s"the offsets of the records they consumed. Deadline in ${timeToDeadlineMillis()}ms. $statusStrings"
+        )
+      }
+
+      def logInitialStreamCompletionStatuses: UIO[Unit] =
+        for {
+          completionStatuses <- getStreamCompletionStatuses(newCommits = Chunk.empty)
+          _                  <- logStreamCompletionStatuses(completionStatuses)
+        } yield ()
+
+      def endingStreamsCompletedAndCommitsExist(newCommits: Chunk[Commit]): UIO[Boolean] =
+        for {
+          completionStatuses <- getStreamCompletionStatuses(newCommits)
+          _                  <- logStreamCompletionStatuses(completionStatuses)
+        } yield completionStatuses.forall { status =>
+          // A stream is complete when it never got any records, or when it committed the offset of the last consumed record
+          status.lastPulledOffset.isEmpty || (status.streamEnded && status.endOffsetCommitStatus != EndOffsetNotCommitted)
         }
 
+      def logFinalStreamCompletionStatuses(completed: Boolean, newCommits: Chunk[Commit]): UIO[Unit] =
+        if (completed)
+          ZIO.logInfo("Continuing rebalance, all offsets of consumed records in the revoked partitions were committed.")
+        else
+          for {
+            completionStatuses <- getStreamCompletionStatuses(newCommits)
+            statusStrings = completionStatusesAsString(completionStatuses)
+            _ <-
+              ZIO.logWarning(
+                s"Exceeded deadline waiting for streams (of revoked partitions) to commit the offsets of " +
+                  s"the records they consumed; the rebalance will continue. " +
+                  s"This might cause another consumer to process some records again. $statusStrings"
+              )
+          } yield ()
+
       def commitSync: Task[Unit] =
         ZIO.attempt(consumer.commitSync(java.util.Collections.emptyMap(), commitTimeout))
 
@@ -179,17 +237,23 @@ private[consumer] final class Runloop private (
       //
       // Note, we cannot use ZStream.fromQueue because that will emit nothing when the queue is empty.
       // Instead, we poll the queue in a loop.
-      ZIO.logDebug(s"Waiting for ${streamsToEnd.size} streams to end") *>
-        ZStream
-          .fromZIO(blockingSleep(commitQueuePollInterval) *> commitQueue.takeAll)
-          .tap(commitAsync)
-          .forever
-          .takeWhile(_ => java.lang.System.nanoTime() <= deadline)
-          .scan(Chunk.empty[Runloop.Commit])(_ ++ _)
-          .takeUntilZIO(endingStreamsCompletedAndCommitsExist)
-          .runDrain *>
-        commitSync *>
-        ZIO.logDebug(s"Done waiting for ${streamsToEnd.size} streams to end")
+      for {
+        _ <- logInitialStreamCompletionStatuses
+        completedAndCommits <-
+          ZStream
+            .fromZIO(blockingSleep(commitQueuePollInterval) *> commitQueue.takeAll)
+            .tap(commitAsync)
+            .forever
+            .takeWhile(_ => java.lang.System.nanoTime() <= deadline)
+            .scan(Chunk.empty[Runloop.Commit])(_ ++ _)
+            .mapZIO(commits => endingStreamsCompletedAndCommitsExist(commits).map((_, commits)))
+            .takeUntil { case (completed, _) => completed }
+            .runLast
+            .map(_.getOrElse((false, Chunk.empty)))
+        _ <- logFinalStreamCompletionStatuses(completedAndCommits._1, completedAndCommits._2)
+        _ <- commitSync
+        _ <- ZIO.logDebug(s"Done waiting for ${streamsToEnd.size} streams to end")
+      } yield ()
     }
 
     // During a poll, the java kafka client might call each method of the rebalance listener 0 or 1 times.