[GitHub] snleee commented on a change in pull request #3852: add support for parquet reader

[GitBox <gi...@apache.org>]

snleee commented on a change in pull request #3852: add support for parquet reader
URL: https://github.com/apache/incubator-pinot/pull/3852#discussion_r261421244
 
 

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 File path: pinot-common/src/main/java/org/apache/pinot/common/utils/ParquetUtils.java
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+/**
+ * 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.pinot.common.utils;
+
+import org.apache.avro.Schema;
+import org.apache.avro.generic.GenericData;
+import org.apache.avro.generic.GenericRecord;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.Path;
+import org.apache.parquet.avro.AvroParquetReader;
+import org.apache.parquet.avro.AvroParquetWriter;
+import org.apache.parquet.avro.AvroSchemaConverter;
+import org.apache.parquet.hadoop.ParquetFileReader;
+import org.apache.parquet.hadoop.ParquetReader;
+import org.apache.parquet.hadoop.ParquetWriter;
+import org.apache.parquet.hadoop.metadata.ParquetMetadata;
+
+import java.io.IOException;
+
+
+public class ParquetUtils {
+  /**
+   * Get a ParquetReader with the given file.
+   * @param fileName the parquet file to read
+   * @return a ParquetReader
+   * @throws IOException
+   */
+  public static ParquetReader<GenericRecord> getParquetReader(String fileName)
+      throws IOException {
+    Path dataFsPath = new Path(fileName);
+    return AvroParquetReader.<GenericRecord>builder(dataFsPath).disableCompatibility().withDataModel(GenericData.get())
+        .withConf(getConfiguration()).build();
+  }
+
+  /**
+   * Read the parquet file schema
+   * @param fileName
+   * @return the parquet file schema
+   * @throws IOException
+   */
+  public static Schema getParquetSchema(String fileName)
+      throws IOException {
+    Path dataFsPath = new Path(fileName);
+    ParquetMetadata footer = ParquetFileReader.readFooter(getConfiguration(), dataFsPath);
+
+    String schemaString = footer.getFileMetaData().getKeyValueMetaData().get("parquet.avro.schema");
+    if (schemaString == null) {
+      // try the older property
+      schemaString = footer.getFileMetaData().getKeyValueMetaData().get("avro.schema");
+    }
+
+    if (schemaString != null) {
+      return new Schema.Parser().parse(schemaString);
+    } else {
+      return new AvroSchemaConverter().convert(footer.getFileMetaData().getSchema());
+    }
+  }
+
+  /**
+   * Get a ParquetWriter with the given file
+   * @param fileName
+   * @param schema
+   * @return a ParquetWriter
+   * @throws IOException
+   */
+  public static ParquetWriter<GenericRecord> getParquetWriter(String fileName, Schema schema)
+      throws IOException {
+    Path dataFsPath = new Path(fileName);
+    return AvroParquetWriter.<GenericRecord>builder(dataFsPath).withSchema(schema).withConf(getConfiguration()).build();
+  }
+
+  private static Configuration getConfiguration() {
+    Configuration conf = new Configuration();
+    conf.set("fs.defaultFS", "file:///");
 
 Review comment:
   Can you add public static final variable for `DEFAULT_FS = "file:///"`? Also, please add the comment on why we need to explicitly set this to `file:///`

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