SreeramGarlapati commented on a change in pull request #2660: URL: https://github.com/apache/iceberg/pull/2660#discussion_r647589121
########## File path: spark3/src/main/java/org/apache/iceberg/spark/source/SparkMicroBatchStream.java ########## @@ -0,0 +1,306 @@ +/* + * 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.iceberg.spark.source; + +import java.io.BufferedWriter; +import java.io.IOException; +import java.io.InputStream; +import java.io.OutputStream; +import java.io.OutputStreamWriter; +import java.nio.charset.StandardCharsets; +import java.util.ArrayList; +import java.util.List; +import java.util.Optional; +import org.apache.iceberg.CombinedScanTask; +import org.apache.iceberg.DataOperations; +import org.apache.iceberg.FileScanTask; +import org.apache.iceberg.MicroBatches; +import org.apache.iceberg.MicroBatches.MicroBatch; +import org.apache.iceberg.Schema; +import org.apache.iceberg.SchemaParser; +import org.apache.iceberg.SerializableTable; +import org.apache.iceberg.Snapshot; +import org.apache.iceberg.Table; +import org.apache.iceberg.io.CloseableIterable; +import org.apache.iceberg.relocated.com.google.common.base.Preconditions; +import org.apache.iceberg.relocated.com.google.common.collect.Iterables; +import org.apache.iceberg.relocated.com.google.common.collect.Lists; +import org.apache.iceberg.spark.Spark3Util; +import org.apache.iceberg.spark.SparkReadOptions; +import org.apache.iceberg.spark.source.SparkBatchScan.ReadTask; +import org.apache.iceberg.spark.source.SparkBatchScan.ReaderFactory; +import org.apache.iceberg.util.PropertyUtil; +import org.apache.iceberg.util.SnapshotUtil; +import org.apache.iceberg.util.TableScanUtil; +import org.apache.spark.api.java.JavaSparkContext; +import org.apache.spark.broadcast.Broadcast; +import org.apache.spark.sql.SparkSession; +import org.apache.spark.sql.connector.read.InputPartition; +import org.apache.spark.sql.connector.read.PartitionReaderFactory; +import org.apache.spark.sql.connector.read.streaming.MicroBatchStream; +import org.apache.spark.sql.connector.read.streaming.Offset; +import org.apache.spark.sql.execution.streaming.HDFSMetadataLog; +import org.apache.spark.sql.util.CaseInsensitiveStringMap; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; +import scala.reflect.ClassTag; + +import static org.apache.iceberg.TableProperties.SPLIT_LOOKBACK; +import static org.apache.iceberg.TableProperties.SPLIT_LOOKBACK_DEFAULT; +import static org.apache.iceberg.TableProperties.SPLIT_OPEN_FILE_COST; +import static org.apache.iceberg.TableProperties.SPLIT_OPEN_FILE_COST_DEFAULT; +import static org.apache.iceberg.TableProperties.SPLIT_SIZE; +import static org.apache.iceberg.TableProperties.SPLIT_SIZE_DEFAULT; + +public class SparkMicroBatchStream implements MicroBatchStream { + private static final Logger LOG = LoggerFactory.getLogger(SparkMicroBatchStream.class); + + private final JavaSparkContext sparkContext; + private final Table table; + private final boolean caseSensitive; + private final Schema expectedSchema; + private final Long splitSize; + private final Integer splitLookback; + private final Long splitOpenFileCost; + private final boolean localityPreferred; + private final OffsetLog offsetLog; + + private StreamingOffset initialOffset = null; + + SparkMicroBatchStream(SparkSession spark, JavaSparkContext sparkContext, + Table table, boolean caseSensitive, Schema expectedSchema, + CaseInsensitiveStringMap options, String checkpointLocation) { + this.sparkContext = sparkContext; + this.table = table; + this.caseSensitive = caseSensitive; + this.expectedSchema = expectedSchema; + this.localityPreferred = Spark3Util.isLocalityEnabled(table.io(), table.location(), options); + this.splitSize = Optional.ofNullable(Spark3Util.propertyAsLong(options, SparkReadOptions.SPLIT_SIZE, null)) + .orElseGet(() -> PropertyUtil.propertyAsLong(table.properties(), SPLIT_SIZE, SPLIT_SIZE_DEFAULT)); + this.splitLookback = Optional.ofNullable(Spark3Util.propertyAsInt(options, SparkReadOptions.LOOKBACK, null)) + .orElseGet(() -> PropertyUtil.propertyAsInt(table.properties(), SPLIT_LOOKBACK, SPLIT_LOOKBACK_DEFAULT)); + this.splitOpenFileCost = Optional.ofNullable( + Spark3Util.propertyAsLong(options, SparkReadOptions.FILE_OPEN_COST, null)) + .orElseGet(() -> PropertyUtil.propertyAsLong(table.properties(), SPLIT_OPEN_FILE_COST, + SPLIT_OPEN_FILE_COST_DEFAULT)); + this.offsetLog = OffsetLog.getInstance(spark, checkpointLocation); + } + + @Override + public Offset latestOffset() { + initialOffset(); + + Snapshot latestSnapshot = table.currentSnapshot(); + if (latestSnapshot == null) { + return StreamingOffset.START_OFFSET; + } + + return new StreamingOffset( + latestSnapshot.snapshotId(), + Iterables.size(latestSnapshot.addedFiles()), + latestSnapshot.snapshotId() == initialOffset.snapshotId()); + } + + @Override + public InputPartition[] planInputPartitions(Offset start, Offset end) { + if (end.equals(StreamingOffset.START_OFFSET)) { + return new InputPartition[0]; + } + + // broadcast the table metadata as input partitions will be sent to executors + Broadcast<Table> tableBroadcast = sparkContext.broadcast(SerializableTable.copyOf(table)); + String expectedSchemaString = SchemaParser.toJson(expectedSchema); + + Preconditions.checkState( + end instanceof StreamingOffset, + "The end offset passed to planInputPartitions() is not an instance of StreamingOffset."); + + Preconditions.checkState( + start instanceof StreamingOffset, + "The start offset passed to planInputPartitions() is not an instance of StreamingOffset."); + + StreamingOffset endOffset = (StreamingOffset) end; + StreamingOffset startOffset = (StreamingOffset) start; + + List<FileScanTask> fileScanTasks = getFileScanTasks(startOffset, endOffset); + + CloseableIterable<FileScanTask> splitTasks = TableScanUtil.splitFiles( + CloseableIterable.withNoopClose(fileScanTasks), + splitSize); + List<CombinedScanTask> combinedScanTasks = Lists.newArrayList( + TableScanUtil.planTasks(splitTasks, splitSize, splitLookback, splitOpenFileCost)); + InputPartition[] readTasks = new InputPartition[combinedScanTasks.size()]; + + for (int i = 0; i < combinedScanTasks.size(); i++) { + readTasks[i] = new ReadTask( + combinedScanTasks.get(i), tableBroadcast, expectedSchemaString, + caseSensitive, localityPreferred); + } + + return readTasks; + } + + @Override + public PartitionReaderFactory createReaderFactory() { + int batchSizeValueToDisableColumnarReads = 0; + return new ReaderFactory(batchSizeValueToDisableColumnarReads); + } + + @Override + public Offset initialOffset() { Review comment: @RussellSpitzer - this comment just means that - although - the streaming data source returns the very initialOffset - it doesn't guarantee that Spark query reads from it. It could choose to ignore it and restart the stream from a check-pointed offset. Overall, I believe, Spark doesn't do a good job in documenting what is needed by a streaming data source. It took a week for me to read thru code in spark codebase - `MicroBatchExecutor` & thoroughly debug thru this data source and fully understand this. I would be happy to hop on to a call and explain - precisely how this works. This implementation is very similar to all other streaming data sources - implemented in spark codebase itself. here's a sample one: https://github.com/apache/spark/blob/0494dc90af48ce7da0625485a4dc6917a244d580/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/RateStreamMicroBatchStream.scala -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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