[SPARK-16963] [STREAMING] [SQL] Changes to Source trait and related implementation classes

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala

@@ -176,6 +176,15 @@ class FileStreamSource(
 
   override def toString: String = s"FileStreamSource[$qualifiedBasePath]"
 
+  /**
+   * Informs the source that Spark has completed processing all data for offsets less than or
+   * equal to `end` and will only request offsets greater than `end` in the future.
+   */
+  override def commit(end: Offset): Unit = {
+    // No-op for now; FileStreamSource currently garbage-collects files based on timestamp
+    // and the value of the maxFileAge parameter.
+  }
+
   override def stop() {}
 }
 

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/Source.scala

@@ -30,16 +30,30 @@ trait Source  {
   /** Returns the schema of the data from this source */
   def schema: StructType
 
-  /** Returns the maximum available offset for this source. */
+  /**
+   * Returns the maximum available offset for this source.
+   * Returns `None` if this source has never received any data.
+   */
   def getOffset: Option[Offset]
 
   /**
-   * Returns the data that is between the offsets (`start`, `end`]. When `start` is `None` then
-   * the batch should begin with the first available record. This method must always return the
-   * same data for a particular `start` and `end` pair.
+   * Returns the data that is between the offsets (`start`, `end`]. When `start` is `None`,
+   * then the batch should begin with the first record. This method must always return the
+   * same data for a particular `start` and `end` pair; even after the Source has been restarted
+   * on a different node.
+   *
+   * Higher layers will always call this method with a value of `start` greater than or equal
+   * to the last value passed to `commit` and a value of `end` less than or equal to the
+   * last value returned by `getOffset`
    */
   def getBatch(start: Option[Offset], end: Offset): DataFrame
 
+  /**
+   * Informs the source that Spark has completed processing all data for offsets less than or
+   * equal to `end` and will only request offsets greater than `end` in the future.
+   */
+  def commit(end: Offset) : Unit = {}
+
   /** Stop this source and free any resources it has allocated. */
   def stop(): Unit
 }

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala

@@ -73,13 +73,19 @@ class StreamExecution(
   /**
    * Tracks how much data we have processed and committed to the sink or state store from each
    * input source.
+   * Only the scheduler thread should modify this field, and only in atomic steps.
+   * Other threads should make a shallow copy if they are going to access this field more than
+   * once, since the field's value may change at any time.
    */
   @volatile
   var committedOffsets = new StreamProgress
 
   /**
    * Tracks the offsets that are available to be processed, but have not yet be committed to the
    * sink.
+   * Only the scheduler thread should modify this field, and only in atomic steps.
+   * Other threads should make a shallow copy if they are going to access this field more than
+   * once, since the field's value may change at any time.
    */
   @volatile
   private var availableOffsets = new StreamProgress
@@ -337,17 +343,27 @@ class StreamExecution(
     }
     if (hasNewData) {
       reportTimeTaken(OFFSET_WAL_WRITE_LATENCY) {
-        assert(
-          offsetLog.add(currentBatchId, availableOffsets.toCompositeOffset(sources)),
+        assert(offsetLog.add(currentBatchId, availableOffsets.toCompositeOffset(sources)),
           s"Concurrent update to the log. Multiple streaming jobs detected for $currentBatchId")
         logInfo(s"Committed offsets for batch $currentBatchId.")
 
+        // NOTE: The following code is correct because runBatches() processes exactly one
+        // batch at a time. If we add pipeline parallelism (multiple batches in flight at
+        // the same time), this cleanup logic will need to change.
+
+        // Now that we've updated the scheduler's persistent checkpoint, it is safe for the
+        // sources to discard data from the previous batch.
+        val prevBatchOff = offsetLog.get(currentBatchId - 1)
+        if (prevBatchOff.isDefined) {
+          prevBatchOff.get.toStreamProgress(sources).foreach {
+            case (src, off) => src.commit(off)
+          }
+        }
+
         // Now that we have logged the new batch, no further processing will happen for
-        // the previous batch, and it is safe to discard the old metadata.
-        // Note that purge is exclusive, i.e. it purges everything before currentBatchId.
-        // NOTE: If StreamExecution implements pipeline parallelism (multiple batches in
-        // flight at the same time), this cleanup logic will need to change.
-        offsetLog.purge(currentBatchId)
+        // the batch before the previous batch, and it is safe to discard the old metadata.
+        // Note that purge is exclusive, i.e. it purges everything before the target ID.
+        offsetLog.purge(currentBatchId - 1)
       }
     } else {
       awaitBatchLock.lock()
@@ -455,7 +471,7 @@ class StreamExecution(
 
   /**
    * Blocks the current thread until processing for data from the given `source` has reached at
-   * least the given `Offset`. This method is indented for use primarily when writing tests.
+   * least the given `Offset`. This method is intended for use primarily when writing tests.
    */
   private[sql] def awaitOffset(source: Source, newOffset: Offset): Unit = {
     def notDone = {

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/memory.scala

@@ -20,7 +20,7 @@ package org.apache.spark.sql.execution.streaming
 import java.util.concurrent.atomic.AtomicInteger
 import javax.annotation.concurrent.GuardedBy
 
-import scala.collection.mutable.ArrayBuffer
+import scala.collection.mutable.{ArrayBuffer, ListBuffer}
 import scala.util.control.NonFatal
 
 import org.apache.spark.internal.Logging
@@ -51,12 +51,23 @@ case class MemoryStream[A : Encoder](id: Int, sqlContext: SQLContext)
   protected val logicalPlan = StreamingExecutionRelation(this)
   protected val output = logicalPlan.output
 
+  /**
+   * All batches from `lastCommittedOffset + 1` to `currentOffset`, inclusive.
+   * Stored in a ListBuffer to facilitate removing committed batches.
+   */
   @GuardedBy("this")
-  protected val batches = new ArrayBuffer[Dataset[A]]
+  protected val batches = new ListBuffer[Dataset[A]]
 
   @GuardedBy("this")
   protected var currentOffset: LongOffset = new LongOffset(-1)
 
+  /**
+   * Last offset that was discarded, or -1 if no commits have occurred. Note that the value
+   * -1 is used in calculations below and isn't just an arbitrary constant.
+   */
+  @GuardedBy("this")
+  protected var lastOffsetCommitted : LongOffset = new LongOffset(-1)
+
   def schema: StructType = encoder.schema
 
   def toDS()(implicit sqlContext: SQLContext): Dataset[A] = {
@@ -85,21 +96,25 @@ case class MemoryStream[A : Encoder](id: Int, sqlContext: SQLContext)
   override def toString: String = s"MemoryStream[${Utils.truncatedString(output, ",")}]"
 
   override def getOffset: Option[Offset] = synchronized {
-    if (batches.isEmpty) {
+    if (currentOffset.offset == -1) {
       None
     } else {
       Some(currentOffset)
     }
   }
 
-  /**
-   * Returns the data that is between the offsets (`start`, `end`].
-   */
   override def getBatch(start: Option[Offset], end: Offset): DataFrame = {
+    // Compute the internal batch numbers to fetch: [startOrdinal, endOrdinal)
     val startOrdinal =
       start.map(_.asInstanceOf[LongOffset]).getOrElse(LongOffset(-1)).offset.toInt + 1
     val endOrdinal = end.asInstanceOf[LongOffset].offset.toInt + 1
-    val newBlocks = synchronized { batches.slice(startOrdinal, endOrdinal) }
+
+    // Internal buffer only holds the batches after lastCommittedOffset.
+    val newBlocks = synchronized {
+      val sliceStart = startOrdinal - lastOffsetCommitted.offset.toInt - 1
+      val sliceEnd = endOrdinal - lastOffsetCommitted.offset.toInt - 1
+      batches.slice(sliceStart, sliceEnd)
+    }
 
     logDebug(
       s"MemoryBatch [$startOrdinal, $endOrdinal]: ${newBlocks.flatMap(_.collect()).mkString(", ")}")
@@ -111,11 +126,29 @@ case class MemoryStream[A : Encoder](id: Int, sqlContext: SQLContext)
       }
   }
 
+  override def commit(end: Offset): Unit = synchronized {
+    end match {
+      case newOffset: LongOffset =>
+        val offsetDiff = (newOffset.offset - lastOffsetCommitted.offset).toInt
+
+        if (offsetDiff < 0) {
+          sys.error(s"Offsets committed out of order: $lastOffsetCommitted followed by $end")
+        }
+
+        batches.trimStart(offsetDiff)
+        lastOffsetCommitted = newOffset
+      case _ =>
+        sys.error(s"MemoryStream.commit() received an offset ($end) that did not originate with " +
+          "an instance of this class")
+    }
+  }
+
   override def stop() {}
 
   def reset(): Unit = synchronized {
     batches.clear()
     currentOffset = new LongOffset(-1)
+    lastOffsetCommitted = new LongOffset(-1)
   }
 }
 

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/socket.scala

@@ -24,14 +24,15 @@ import java.text.SimpleDateFormat
 import java.util.Calendar
 import javax.annotation.concurrent.GuardedBy
 
-import scala.collection.mutable.ArrayBuffer
+import scala.collection.mutable.ListBuffer
 import scala.util.{Failure, Success, Try}
 
 import org.apache.spark.internal.Logging
-import org.apache.spark.sql.{AnalysisException, DataFrame, SQLContext}
+import org.apache.spark.sql._
 import org.apache.spark.sql.sources.{DataSourceRegister, StreamSourceProvider}
 import org.apache.spark.sql.types.{StringType, StructField, StructType, TimestampType}
 
+
 object TextSocketSource {
   val SCHEMA_REGULAR = StructType(StructField("value", StringType) :: Nil)
   val SCHEMA_TIMESTAMP = StructType(StructField("value", StringType) ::
@@ -53,8 +54,18 @@ class TextSocketSource(host: String, port: Int, includeTimestamp: Boolean, sqlCo
   @GuardedBy("this")
   private var readThread: Thread = null
 
+  /**
+   * All batches from `lastCommittedOffset + 1` to `currentOffset`, inclusive.
+   * Stored in a ListBuffer to facilitate removing committed batches.
+   */
+  @GuardedBy("this")
+  protected val batches = new ListBuffer[(String, Timestamp)]
+
+  @GuardedBy("this")
+  protected var currentOffset: LongOffset = new LongOffset(-1)
+
   @GuardedBy("this")
-  private var lines = new ArrayBuffer[(String, Timestamp)]
+  protected var lastOffsetCommitted : LongOffset = new LongOffset(-1)
 
   initialize()
 
@@ -74,10 +85,12 @@ class TextSocketSource(host: String, port: Int, includeTimestamp: Boolean, sqlCo
               return
             }
             TextSocketSource.this.synchronized {
-              lines += ((line,
+              val newData = (line,
                 Timestamp.valueOf(
                   TextSocketSource.DATE_FORMAT.format(Calendar.getInstance().getTime()))
-                ))
+                )
+              currentOffset = currentOffset + 1
+              batches.append(newData)
             }
           }
         } catch {
@@ -92,21 +105,54 @@ class TextSocketSource(host: String, port: Int, includeTimestamp: Boolean, sqlCo
   override def schema: StructType = if (includeTimestamp) TextSocketSource.SCHEMA_TIMESTAMP
   else TextSocketSource.SCHEMA_REGULAR
 
-  /** Returns the maximum available offset for this source. */
   override def getOffset: Option[Offset] = synchronized {
-    if (lines.isEmpty) None else Some(LongOffset(lines.size - 1))
+    if (currentOffset.offset == -1) {
+      None
+    } else {
+      Some(currentOffset)
+    }
   }
 
   /** Returns the data that is between the offsets (`start`, `end`]. */
   override def getBatch(start: Option[Offset], end: Offset): DataFrame = synchronized {
-    val startIdx = start.map(_.asInstanceOf[LongOffset].offset.toInt + 1).getOrElse(0)
-    val endIdx = end.asInstanceOf[LongOffset].offset.toInt + 1
-    val data = synchronized { lines.slice(startIdx, endIdx) }
+    val startOrdinal =
+      start.map(_.asInstanceOf[LongOffset]).getOrElse(LongOffset(-1)).offset.toInt + 1
+    val endOrdinal = end.asInstanceOf[LongOffset].offset.toInt + 1
+
+    // Internal buffer only holds the batches after lastOffsetCommitted
+    val rawList = synchronized {
+      val sliceStart = startOrdinal - lastOffsetCommitted.offset.toInt - 1
+      val sliceEnd = endOrdinal - lastOffsetCommitted.offset.toInt - 1
+      batches.slice(sliceStart, sliceEnd)
+    }
+
     import sqlContext.implicits._
+    val rawBatch = sqlContext.createDataset(rawList)
+
+    // Underlying MemoryStream has schema (String, Timestamp); strip out the timestamp
+    // if requested.
     if (includeTimestamp) {
-      data.toDF("value", "timestamp")
+      rawBatch.toDF("value", "timestamp")
+    } else {
+      // Strip out timestamp
+      rawBatch.select("_1").toDF("value")
+    }
+  }
+
+  override def commit(end: Offset): Unit = synchronized {
+    if (end.isInstanceOf[LongOffset]) {
+      val newOffset = end.asInstanceOf[LongOffset]
+      val offsetDiff = (newOffset.offset - lastOffsetCommitted.offset).toInt
+
+      if (offsetDiff < 0) {
+        sys.error(s"Offsets committed out of order: $lastOffsetCommitted followed by $end")
+      }
+
+      batches.trimStart(offsetDiff)
+      lastOffsetCommitted = newOffset
     } else {
-      data.map(_._1).toDF("value")
+      sys.error(s"TextSocketStream.commit() received an offset ($end) that did not " +
+        s"originate with an instance of this class")
     }
   }
 
@@ -141,7 +187,7 @@ class TextSocketSourceProvider extends StreamSourceProvider with DataSourceRegis
       providerName: String,
       parameters: Map[String, String]): (String, StructType) = {
     logWarning("The socket source should not be used for production applications! " +
-      "It does not support recovery and stores state indefinitely.")
+      "It does not support recovery.")
     if (!parameters.contains("host")) {
       throw new AnalysisException("Set a host to read from with option(\"host\", ...).")
     }

sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQuerySuite.scala

@@ -252,8 +252,8 @@ class StreamingQuerySuite extends StreamTest with BeforeAndAfter with Logging {
     val inputData = MemoryStream[Int]
     val mapped = inputData.toDS().map(6 / _)
 
-    // Run 3 batches, and then assert that only 1 metadata file is left at the end
-    // since the first 2 should have been purged.
+    // Run 3 batches, and then assert that only 2 metadata files is are at the end
+    // since the first should have been purged.
     testStream(mapped)(
       AddData(inputData, 1, 2),
       CheckAnswer(6, 3),
@@ -262,11 +262,11 @@ class StreamingQuerySuite extends StreamTest with BeforeAndAfter with Logging {
       AddData(inputData, 4, 6),
       CheckAnswer(6, 3, 6, 3, 1, 1),
 
-      AssertOnQuery("metadata log should contain only one file") { q =>
+      AssertOnQuery("metadata log should contain only two files") { q =>
         val metadataLogDir = new java.io.File(q.offsetLog.metadataPath.toString)
         val logFileNames = metadataLogDir.listFiles().toSeq.map(_.getName())
         val toTest = logFileNames.filter(! _.endsWith(".crc"))  // Workaround for SPARK-17475
-        assert(toTest.size == 1 && toTest.head == "2")
+        assert(toTest.size == 2 && toTest.head == "1")
         true
       }
     )