viirya commented on a change in pull request #33763:
URL: https://github.com/apache/spark/pull/33763#discussion_r697823961



##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/AvailableNowDataStreamWrapper.scala
##########
@@ -0,0 +1,85 @@
+/*
+ * 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
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.connector.read.streaming.{MicroBatchStream, 
ReadLimit, SparkDataStream, SupportsAdmissionControl, 
SupportsTriggerAvailableNow}
+import org.apache.spark.sql.connector.read.streaming
+
+/**
+ * This class wraps a [[SparkDataStream]] and makes it support 
Trigger.AvailableNow, by
+ * overriding its [[latestOffset]] method to always return the latest offset 
when the method is
+ * first called. It is as if there is no new data coming in from the source 
after the first
+ * [[latestOffset]] call.
+ */
+class AvailableNowDataStreamWrapper(val delegate: SparkDataStream)
+  extends SparkDataStream with SupportsTriggerAvailableNow with Logging {
+
+  private var fetchedOffset: Option[streaming.Offset] = _
+
+  override def initialOffset(): streaming.Offset = delegate.initialOffset()
+
+  override def deserializeOffset(json: String): streaming.Offset = 
delegate.deserializeOffset(json)
+
+  override def commit(end: streaming.Offset): Unit = delegate.commit(end)
+
+  override def stop(): Unit = delegate.stop()
+
+  override def prepareForTriggerAvailableNow(): Unit = {}

Review comment:
       As this implements `SupportsTriggerAvailableNow`, but seems 
`prepareForTriggerAvailableNow` is useless? Why don't we record latest offset 
here?

##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
##########
@@ -105,6 +109,8 @@ class FileStreamSource(
   // Visible for testing and debugging in production.
   val seenFiles = new SeenFilesMap(maxFileAgeMs, fileNameOnly)
 
+  var allFilesForTriggerAvailableNow: Seq[(String, Long)] = null

Review comment:
       `private`?

##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/MicroBatchExecution.scala
##########
@@ -382,6 +404,22 @@ class MicroBatchExecution(
 
     // Generate a map from each unique source to the next available offset.
     val (nextOffsets, recentOffsets) = uniqueSources.toSeq.map {
+      case (s: AvailableNowDataStreamWrapper, limit) =>
+        val originalSource = s.delegate
+        updateStatusMessage(s"Getting offsets from $s")
+        reportTimeTaken("latestOffset") {
+          val startOffsetOpt = availableOffsets.get(originalSource)
+          val startOffset = s match {

Review comment:
       here shouldn't we match against `originalSource`?

##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
##########
@@ -126,7 +132,12 @@ class FileStreamSource(
       unreadFiles
     } else {
       // All the new files found - ignore aged files and files that we have 
seen.

Review comment:
       Should this comment follow `fetchAllFiles`?

##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/MicroBatchExecution.scala
##########
@@ -121,18 +122,36 @@ class MicroBatchExecution(
       // v2 source
       case r: StreamingDataSourceV2Relation => r.stream
     }
-    uniqueSources = sources.distinct.map {
-      case source: SupportsAdmissionControl =>
-        val limit = source.getDefaultReadLimit
-        if (trigger == OneTimeTrigger && limit != ReadLimit.allAvailable()) {
-          logWarning(s"The read limit $limit for $source is ignored when 
Trigger.Once() is used.")
-          source -> ReadLimit.allAvailable()
-        } else {
-          source -> limit
-        }
-      case other =>
-        other -> ReadLimit.allAvailable()
-    }.toMap
+    uniqueSources = triggerExecutor match {
+      case _: SingleBatchExecutor =>
+        sources.distinct.map {
+          case s: SupportsAdmissionControl =>
+            val limit = s.getDefaultReadLimit
+            if (limit != ReadLimit.allAvailable()) {
+              logWarning(
+                s"The read limit $limit for $s is ignored when Trigger.Once is 
used.")
+            }
+            s -> ReadLimit.allAvailable()
+          case s =>
+            s -> ReadLimit.allAvailable()
+        }.toMap
+
+      case _: MultiBatchExecutor =>
+        sources.distinct.map {
+          case s: SupportsTriggerAvailableNow => s
+          case s: Source => new AvailableNowSourceWrapper(s)
+          case s: MicroBatchStream => new 
AvailableNowMicroBatchStreamWrapper(s)
+        }.map { s =>
+          s.prepareForTriggerAvailableNow()
+          s -> s.getDefaultReadLimit

Review comment:
       Should we log warning if it is `getDefaultReadLimit` is 
`ReadLimit.allAvailable()` for `AvailableNowTrigger`?




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