Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/9774#discussion_r45235636
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/UnsafeRowParquetRecordReader.java
---
@@ -0,0 +1,613 @@
+/*
+ * 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.Preconditions;
+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.OriginalType;
+import org.apache.parquet.schema.PrimitiveType;
+import org.apache.parquet.schema.Type;
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow;
+import org.apache.spark.sql.types.Decimal;
+import org.apache.spark.unsafe.Platform;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.*;
+
+/**
+ * A specialized RecordReader that reads into UnsafeRows directly using
the Parquet column APIs.
+ *
+ * This is somewhat based on parquet-mr's ColumnReader.
+ *
+ * TODO: handle complex types, decimal requiring more than 8 bytes, INT96.
Schema mismatch.
+ * All of these can be handled efficiently and easily with codegen.
+ */
+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;
+
+ /**
+ * Used to write variable lenght columns. Same length as `rows`.
+ */
+ private RowWriter[] rowWriters = null;
+
+ /**
+ * True if the row contains variable length fields.
+ */
+ private boolean containsVarLenFields;
+
+ /**
+ * 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;
+
+ /**
+ * For each column, the annotated original type.
+ */
+ OriginalType[] originalTypes;
+
+ /**
+ * Implementation of RecordReader API.
+ */
+ @Override
+ public void initialize(InputSplit inputSplit, TaskAttemptContext
taskAttemptContext)
+ throws IOException, InterruptedException {
+ super.initialize(inputSplit, taskAttemptContext);
+
+ /**
+ * Check that the requested schema is supported.
+ */
+ int numVarLenFields = 0;
+ originalTypes = new OriginalType[requestedSchema.getFieldCount()];
+ for (int i = 0; i < requestedSchema.getFieldCount(); ++i) {
+ Type t = requestedSchema.getFields().get(i);
+ if (!t.isPrimitive()) throw new IOException("Complex types not
supported.");
+ PrimitiveType primitiveType = t.asPrimitiveType();
+
+ originalTypes[i] = t.getOriginalType();
+
+ // TODO: Be extremely cautious in what is supported. Expand this.
--- End diff --
Could we move this logic to where we are deciding which reader to
instantiate instead of using exceptions for control flow?
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