diff --git a/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/Dispatcher.scala b/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/Dispatcher.scala
index 81a1c06f..5163f24c 100644
--- a/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/Dispatcher.scala
+++ b/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/Dispatcher.scala
@@ -117,7 +117,7 @@ object Dispatcher {
       override def revoke(partitions: Set[TopicPartition]): URIO[GreyhoundMetrics, Unit] =
         workers
           .modify { workers =>
-            val revoked = workers.filterKeys(partitions.contains)
+            val revoked   = workers.filterKeys(partitions.contains)
             val remaining = workers -- partitions
 
             (revoked, remaining)
@@ -246,13 +246,23 @@ object Dispatcher {
       queue         <- Queue.dropping[Record](capacity)
       internalState <- TRef.make(WorkerInternalState.empty).commit
       fiber         <-
-        (reportWorkerRunningInInterval(every = 60.seconds, internalState)(partition, group, clientId).forkDaemon *>
-          (if (consumeInParallel)
-              pollBatch(status, internalState, handle, queue, group, clientId, partition, consumerAttributes, maxParallelism, updateBatch, currentGaps)
-            else pollOnce(status, internalState, handle, queue, group, clientId, partition, consumerAttributes))
-              .repeatWhile(_ == true))
-          .interruptible
-          .forkDaemon
+      (reportWorkerRunningInInterval(every = 60.seconds, internalState)(partition, group, clientId).forkDaemon *>
+        (if (consumeInParallel)
+           pollBatch(
+             status,
+             internalState,
+             handle,
+             queue,
+             group,
+             clientId,
+             partition,
+             consumerAttributes,
+             maxParallelism,
+             updateBatch,
+             currentGaps
+           )
+         else pollOnce(status, internalState, handle, queue, group, clientId, partition, consumerAttributes))
+          .repeatWhile(_ == true)).interruptible.forkDaemon
     } yield new Worker {
       override def submit(record: Record): URIO[Any, Boolean] =
         queue
@@ -406,17 +416,18 @@ object Dispatcher {
                               )
         groupedRecords    = records.groupBy(_.key).values // todo: add sub-grouping for records without key
         latestCommitGaps <- currentGaps(records.map(r => TopicPartition(r.topic, r.partition)).toSet)
-        _                <- ZIO
-                              .foreachParDiscard(groupedRecords)(sameKeyRecords =>
-                                ZIO.foreach(sameKeyRecords) { record =>
-                                  if (shouldRecordBeHandled(record, latestCommitGaps)) {
-                                    handle(record).interruptible.ignore *> updateBatch(sameKeyRecords).interruptible
-                                  } else
-                                    report(SkippedPreviouslyHandledRecord(record, group, clientId, consumerAttributes))
-
-                                }
-                              )
-                              .withParallelism(maxParallelism)
+        _                <- report(InvokingHandlersInParallel(Math.max(groupedRecords.size, maxParallelism))) *>
+                              ZIO
+                                .foreachParDiscard(groupedRecords)(sameKeyRecords =>
+                                  ZIO.foreach(sameKeyRecords) { record =>
+                                    if (shouldRecordBeHandled(record, latestCommitGaps)) {
+                                      handle(record).interruptible.ignore *> updateBatch(sameKeyRecords).interruptible
+                                    } else
+                                      report(SkippedPreviouslyHandledRecord(record, group, clientId, consumerAttributes))
+
+                                  }
+                                )
+                                .withParallelism(maxParallelism)
         res              <- isActive(internalState)
       } yield res
   }
@@ -568,6 +579,8 @@ object DispatcherMetric {
     currentExecutionStarted: Option[Long]
   ) extends DispatcherMetric
 
+  case class InvokingHandlersInParallel(numHandlers: Int) extends DispatcherMetric
+
   case class SkippedPreviouslyHandledRecord(record: Record, group: Group, clientId: ClientId, attributes: Map[String, String])
       extends DispatcherMetric
 
diff --git a/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/EventLoop.scala b/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/EventLoop.scala
index fd291da0..62f9c638 100644
--- a/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/EventLoop.scala
+++ b/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/EventLoop.scala
@@ -296,7 +296,7 @@ object EventLoop {
       val offsetsAndMetadataToCommit = OffsetsAndGaps.toOffsetsAndMetadata(committable)
       consumer
         .commitWithMetadata(offsetsAndMetadataToCommit)
-        .tap(_ => report(CommittedOffsetsAndMetadata(offsetsAndMetadataToCommit)))
+        .tap(_ => ZIO.when(offsetsAndMetadataToCommit.nonEmpty)(report(CommittedOffsetsAndMetadata(offsetsAndMetadataToCommit))))
         .catchAll { t =>
           report(FailedToCommitOffsetsAndMetadata(t, offsetsAndMetadataToCommit)) *> offsetsAndGaps.setCommittable(committable)
         }
@@ -331,7 +331,8 @@ object EventLoop {
                        .commitWithMetadataOnRebalance(OffsetsAndGaps.toOffsetsAndMetadata(committable))
                        .catchAll { _ => offsetsAndGaps.setCommittable(committable) *> DelayedRebalanceEffect.zioUnit }
       runtime     <- ZIO.runtime[Any]
-    } yield tle.catchAll { _ => zio.Unsafe.unsafe { implicit s =>
+    } yield tle.catchAll { _ =>
+      zio.Unsafe.unsafe { implicit s =>
         runtime.unsafe
           .run(offsetsAndGaps.setCommittable(committable))
           .getOrThrowFiberFailure()
@@ -407,6 +408,14 @@ object EventLoopMetric {
 
   case class FailedToUpdatePositions(t: Throwable, clientId: ClientId, attributes: Map[String, String] = Map.empty) extends EventLoopMetric
 
+  case class FailedToUpdateGapsOnPartitionAssignment(
+    t: Throwable,
+    clientId: ClientId,
+    group: Group,
+    partitions: Set[TopicPartition],
+    attributes: Map[String, String] = Map.empty
+  ) extends EventLoopMetric
+
   case class FailedToFetchCommittedGaps(t: Throwable, clientId: ClientId, attributes: Map[String, String] = Map.empty)
       extends EventLoopMetric
 
diff --git a/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/OffsetsAndGaps.scala b/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/OffsetsAndGaps.scala
index 2704b5d6..b2e68bca 100644
--- a/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/OffsetsAndGaps.scala
+++ b/core/src/main/scala/com/wixpress/dst/greyhound/core/consumer/OffsetsAndGaps.scala
@@ -11,16 +11,19 @@ trait OffsetsAndGaps {
 
   def gapsForPartition(partition: TopicPartition): UIO[Seq[Gap]]
 
-  def update(partition: TopicPartition, batch: Seq[Offset]): UIO[Unit]
+  def update(partition: TopicPartition, batch: Seq[Offset], prevCommittedOffset: Option[Offset]): UIO[Unit]
 
   def update(record: ConsumerRecord[_, _]): UIO[Unit] =
-    update(RecordTopicPartition(record), Seq(record.offset))
+    update(RecordTopicPartition(record), Seq(record.offset), None)
 
   def update(records: Chunk[ConsumerRecord[_, _]]): UIO[Unit] = {
     val sortedBatch = records.sortBy(_.offset)
-    update(RecordTopicPartition(sortedBatch.head), sortedBatch.map(_.offset) ++ Seq(sortedBatch.last.offset + 1))
+    update(RecordTopicPartition(sortedBatch.head), sortedBatch.map(_.offset) ++ Seq(sortedBatch.last.offset + 1), None)
   }
 
+  def update(partition: TopicPartition, batch: Seq[Offset]): UIO[Unit] =
+    update(partition, batch, None)
+
   def setCommittable(offsets: Map[TopicPartition, OffsetAndGaps]): UIO[Unit]
 
   def contains(partition: TopicPartition, offset: Offset): UIO[Boolean]
@@ -40,7 +43,7 @@ object OffsetsAndGaps {
         override def gapsForPartition(partition: TopicPartition): UIO[Seq[Gap]] =
           ref.get.map(_.get(partition).fold(Seq.empty[Gap])(_.gaps.sortBy(_.start)))
 
-        override def update(partition: TopicPartition, batch: Seq[Offset]): UIO[Unit] =
+        override def update(partition: TopicPartition, batch: Seq[Offset], prevCommittedOffset: Option[Offset]): UIO[Unit] =
           ref.update { offsetsAndGaps =>
             val sortedBatch            = batch.sorted
             val maxBatchOffset         = sortedBatch.last