Github user julienledem commented on a diff in the pull request:
https://github.com/apache/spark/pull/9774#discussion_r45162142
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/UnsafeRowParquetRecordReader.java
---
@@ -0,0 +1,428 @@
+/*
+ * 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.datasources.parquet;
+
+import static org.apache.parquet.column.ValuesType.DEFINITION_LEVEL;
+import static org.apache.parquet.column.ValuesType.REPETITION_LEVEL;
+import static org.apache.parquet.column.ValuesType.VALUES;
+
+import org.apache.hadoop.mapreduce.InputSplit;
+import org.apache.hadoop.mapreduce.TaskAttemptContext;
+import org.apache.parquet.column.ColumnDescriptor;
+import org.apache.parquet.column.Dictionary;
+import org.apache.parquet.column.page.*;
+import org.apache.parquet.column.Encoding;
+import org.apache.parquet.column.values.ValuesReader;
+import org.apache.parquet.io.api.Binary;
+import org.apache.parquet.schema.Type;
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow;
+import org.apache.spark.unsafe.Platform;
+
+import java.io.IOException;
+import java.util.*;
+
+/**
+ * A specialized RecordReader that reads into UnsafeRows directly using
the Parquet column APIs.
+ *
+ * TODO: handle complex types.
+ */
+public class UnsafeRowParquetRecordReader extends
SpecificParquetRecordReaderBase<UnsafeRow> {
+ /**
+ * Batch of unsafe rows that we assemble and the current index we've
returned. Everytime this
+ * batch is used up (batchIdx == numBatched), we populated the batch.
+ */
+ private UnsafeRow[] rows = new UnsafeRow[64];
+ private int batchIdx = 0;
+ private int numBatched = 0;
+
+ /**
+ * For each request column, the reader to read this column.
+ * columnsReaders[i] populated the UnsafeRow's attribute at i.
+ */
+ private ColumnReader[] columnReaders;
+
+ /**
+ * The number of rows that have been returned.
+ */
+ private long rowsReturned;
+
+ /**
+ * The number of rows that have been reading, including the current in
flight row group.
+ */
+ private long totalCountLoadedSoFar = 0;
+
+ /**
+ * Implementation of RecordReader API.
+ */
+ @Override
+ public void initialize(InputSplit inputSplit, TaskAttemptContext
taskAttemptContext)
+ throws IOException, InterruptedException {
+ super.initialize(inputSplit, taskAttemptContext);
+
+ int rowByteSize =
UnsafeRow.calculateBitSetWidthInBytes(requestedSchema.getFieldCount());
+ rowByteSize += 8 * requestedSchema.getFieldCount();
+
+ byte[] buffer = new byte[rowByteSize * rows.length];
+ for (int i = 0; i < rows.length; ++i) {
+ rows[i] = new UnsafeRow();
+ rows[i].pointTo(buffer, Platform.BYTE_ARRAY_OFFSET + i * rowByteSize,
+ requestedSchema.getFieldCount(), rowByteSize);
+ }
+
+ /**
+ * Check that the requested schema is supported.
+ */
+ for (Type t: requestedSchema.getFields()) {
+ if (!t.isPrimitive()) throw new IOException("Unsupported schema");
+ }
+
+ // TODO: this needs to handle the schema resolution rules
+ }
+
+ @Override
+ public boolean nextKeyValue() throws IOException, InterruptedException {
+ if (batchIdx >= numBatched) {
+ if (!loadBatch()) return false;
+ }
+ ++batchIdx;
+ return true;
+ }
+
+ @Override
+ public UnsafeRow getCurrentValue() throws IOException,
InterruptedException {
+ return rows[batchIdx - 1];
+ }
+
+ @Override
+ public float getProgress() throws IOException, InterruptedException {
+ return (float) rowsReturned / totalRowCount;
+ }
+
+ /**
+ * Decodes a batch of values into `rows`. This function is the hot path.
+ */
+ private boolean loadBatch() throws IOException {
+ // no more records left
+ if (rowsReturned >= totalRowCount) { return false; }
+ checkEndOfRowGroup();
+
+ int num = (int)Math.min(rows.length, totalCountLoadedSoFar -
rowsReturned);
+ rowsReturned += num;
+
+ for (int i = 0; i < columnReaders.length; ++i) {
+ switch (columnReaders[i].descriptor.getType()) {
+ case BOOLEAN:
+ decodeBooleanBatch(i, num);
+ break;
+ case INT32:
+ decodeIntBatch(i, num);
+ break;
+ case INT64:
+ decodeLongBatch(i, num);
+ break;
+ case FLOAT:
+ decodeFloatBatch(i, num);
+ break;
+ case DOUBLE:
+ decodeDoubleBatch(i, num);
+ break;
+ }
+ numBatched = num;
+ batchIdx = 0;
+ }
+ return true;
+ }
+
+ private void decodeBooleanBatch(int col, int num) throws IOException {
+ for (int n = 0; n < num; ++n) {
+ if (columnReaders[col].next() != 0) {
+ rows[n].setBoolean(col, columnReaders[col].nextBoolean());
+ } else {
+ rows[n].setNullAt(col);
+ }
+ }
+ }
+
+ private void decodeIntBatch(int col, int num) throws IOException {
+ for (int n = 0; n < num; ++n) {
+ if (columnReaders[col].next() != 0) {
+ rows[n].setInt(col, columnReaders[col].nextInt());
+ } else {
+ rows[n].setNullAt(col);
+ }
+ }
+ }
+
+ private void decodeLongBatch(int col, int num) throws IOException {
+ for (int n = 0; n < num; ++n) {
+ if (columnReaders[col].next() != 0) {
+ rows[n].setLong(col, columnReaders[col].nextLong());
+ } else {
+ rows[n].setNullAt(col);
+ }
+ }
+ }
+
+ private void decodeFloatBatch(int col, int num) throws IOException {
+ for (int n = 0; n < num; ++n) {
+ if (columnReaders[col].next() != 0) {
+ rows[n].setFloat(col, columnReaders[col].nextFloat());
+ } else {
+ rows[n].setNullAt(col);
+ }
+ }
+ }
+
+ private void decodeDoubleBatch(int col, int num) throws IOException {
+ for (int n = 0; n < num; ++n) {
+ if (columnReaders[col].next() != 0) {
+ rows[n].setDouble(col, columnReaders[col].nextDouble());
+ } else {
+ rows[n].setNullAt(col);
+ }
+ }
+ }
+
+ /**
+ *
+ * Decoder to return values from a single column.
+ */
+ private static final class ColumnReader {
+ /**
+ * Total number of values read.
+ */
+ private long valuesRead;
+
+ /**
+ * value that indicates the end of the current page. That is,
+ * if valuesRead == endOfPageValueCount, we are at the end of the page.
+ */
+ private long endOfPageValueCount;
+
+ /**
+ * The dictionary, if this column has dictionary encoding.
+ */
+ private final Dictionary dictionary;
+
+ /**
+ * If true, the current page is dictionary encoded.
+ */
+ private boolean useDictionary;
+
+ /**
+ * Repetition/Definition/Value readers.
+ */
+ private IntIterator repetitionLevelColumn;
+ private IntIterator definitionLevelColumn;
+ private ValuesReader dataColumn;
+
+ /**
+ * Total number of values in this column (in this row group).
+ */
+ private final long totalValueCount;
+
+ /**
+ * Total values in the current page.
+ */
+ private int pageValueCount;
+
+ private PageReader pageReader;
+ private ColumnDescriptor descriptor;
+
+ public ColumnReader(ColumnDescriptor descriptor, PageReader
pageReader) throws IOException {
+ this.descriptor = descriptor;
+ this.pageReader = pageReader;
+
+ DictionaryPage dictionaryPage = pageReader.readDictionaryPage();
+ if (dictionaryPage != null) {
+ try {
+ this.dictionary =
dictionaryPage.getEncoding().initDictionary(descriptor, dictionaryPage);
+ this.useDictionary = true;
+ } catch (IOException e) {
+ throw new IOException("could not decode the dictionary for " +
descriptor, e);
+ }
+ } else {
+ this.dictionary = null;
+ this.useDictionary = false;
+ }
+ this.totalValueCount = pageReader.getTotalValueCount();
+ if (totalValueCount == 0) {
+ throw new IOException("totalValueCount == 0");
+ }
+ }
+
+ /**
+ * TODO: Hoist the useDictionary branch to decode*Batch and make the
batch page aligned.
+ */
+ public boolean nextBoolean() {
+ if (!useDictionary) {
+ return dataColumn.readBoolean();
+ } else {
+ return
dictionary.decodeToBoolean(dataColumn.readValueDictionaryId());
+ }
+ }
+
+ public int nextInt() {
+ if (!useDictionary) {
+ return dataColumn.readInteger();
+ } else {
+ return dictionary.decodeToInt(dataColumn.readValueDictionaryId());
+ }
+ }
+
+ public long nextLong() {
+ if (!useDictionary) {
+ return dataColumn.readLong();
+ } else {
+ return dictionary.decodeToLong(dataColumn.readValueDictionaryId());
+ }
+ }
+
+ public float nextFloat() {
+ if (!useDictionary) {
+ return dataColumn.readFloat();
+ } else {
+ return
dictionary.decodeToFloat(dataColumn.readValueDictionaryId());
+ }
+ }
+
+ public double nextDouble() {
+ if (!useDictionary) {
+ return dataColumn.readDouble();
+ } else {
+ return
dictionary.decodeToDouble(dataColumn.readValueDictionaryId());
+ }
+ }
+
+ public Binary nextBinary() {
+ if (!useDictionary) {
+ return dataColumn.readBytes();
+ } else {
+ return
dictionary.decodeToBinary(dataColumn.readValueDictionaryId());
+ }
+ }
+
+ private int next() throws IOException {
+ if (valuesRead >= endOfPageValueCount) {
+ if (valuesRead >= totalValueCount) {
+ // How do we get here? Throw end of stream exception?
+ return 0;
+ }
+ readPage();
+ }
+ ++valuesRead;
+ // TODO: Don't read for flat schemas
+ //repetitionLevel = repetitionLevelColumn.nextInt();
+ return definitionLevelColumn.nextInt();
+ }
+
+ private void readPage() throws IOException {
+ DataPage page = pageReader.readPage();
+ // TODO: Why is this a visitor?
--- End diff --
well, you can use instanceof and casts, is that what you are getting at?
the visitor is type safe ;)
In Scala you would just use patter matching:
```
page match {
case dataPageV1: DataPageV1 => readPageV1(dataPageV1)
case dataPageV2: DataPageV2 => readPageV2(dataPageV2)
}
```
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