Github user HeartSaVioR commented on a diff in the pull request:
https://github.com/apache/spark/pull/21200#discussion_r185200004
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/EpochPollRunnable.scala
---
@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.streaming.continuous
+
+import java.util.concurrent.BlockingQueue
+import java.util.concurrent.atomic.AtomicBoolean
+
+import org.apache.spark.{SparkEnv, TaskContext}
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.sql.sources.v2.reader.streaming.PartitionOffset
+
+/**
+ * The epoch marker component of [[ContinuousQueuedDataReader]]. Populates
the queue with
+ * (null, null) when a new epoch marker arrives.
+ */
+class EpochPollRunnable(
+ queue: BlockingQueue[(UnsafeRow, PartitionOffset)],
+ context: TaskContext,
+ failedFlag: AtomicBoolean)
+ extends Thread with Logging {
+ private[continuous] var failureReason: Throwable = _
+
+ private val epochEndpoint = EpochCoordinatorRef.get(
+
context.getLocalProperty(ContinuousExecution.EPOCH_COORDINATOR_ID_KEY),
SparkEnv.get)
+ // Note that this is *not* the same as the currentEpoch in
[[ContinuousDataQueuedReader]]! That
+ // field represents the epoch wrt the data being processed. The
currentEpoch here is just a
+ // counter to ensure we send the appropriate number of markers if we
fall behind the driver.
+ private var currentEpoch =
context.getLocalProperty(ContinuousExecution.START_EPOCH_KEY).toLong
+
+ override def run(): Unit = {
+ try {
+ val newEpoch = epochEndpoint.askSync[Long](GetCurrentEpoch)
+ for (i <- currentEpoch to newEpoch - 1) {
--- End diff --
Please correct me if I'm missing. My understanding is that the situation
(gap bigger than 1) should only occur when array queue gets full and blocks
epoch thread to put marker more than trigger interval. Any other situations
(error cases) should just crash the whole query so that recovery happens from
the scratch: that's why we can ignore the missing case.
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