rdblue commented on a change in pull request #843: [WIP] InputFormat support 
for Iceberg
URL: https://github.com/apache/incubator-iceberg/pull/843#discussion_r393228871
 
 

 ##########
 File path: mr/src/main/java/org/apache/iceberg/mr/IcebergInputFormat.java
 ##########
 @@ -0,0 +1,345 @@
+/*
+ * 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.mr;
+
+import com.google.common.collect.Iterators;
+import com.google.common.collect.Lists;
+import java.io.Closeable;
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Set;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.mapreduce.InputFormat;
+import org.apache.hadoop.mapreduce.InputSplit;
+import org.apache.hadoop.mapreduce.JobContext;
+import org.apache.hadoop.mapreduce.RecordReader;
+import org.apache.hadoop.mapreduce.TaskAttemptContext;
+import org.apache.iceberg.CombinedScanTask;
+import org.apache.iceberg.DataFile;
+import org.apache.iceberg.FileScanTask;
+import org.apache.iceberg.PartitionSpec;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.SchemaParser;
+import org.apache.iceberg.Table;
+import org.apache.iceberg.TableScan;
+import org.apache.iceberg.avro.Avro;
+import org.apache.iceberg.catalog.Catalog;
+import org.apache.iceberg.catalog.TableIdentifier;
+import org.apache.iceberg.common.DynClasses;
+import org.apache.iceberg.exceptions.RuntimeIOException;
+import org.apache.iceberg.expressions.Expression;
+import org.apache.iceberg.hadoop.HadoopInputFile;
+import org.apache.iceberg.hadoop.HadoopTables;
+import org.apache.iceberg.hive.HiveCatalogs;
+import org.apache.iceberg.io.CloseableIterable;
+import org.apache.iceberg.io.InputFile;
+import org.apache.iceberg.orc.ORC;
+import org.apache.iceberg.parquet.Parquet;
+import org.apache.iceberg.types.TypeUtil;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class IcebergInputFormat<T> extends InputFormat<Void, T> {
+  private static final Logger LOG = 
LoggerFactory.getLogger(IcebergInputFormat.class);
+
+  static final String FILTER_EXPRESSION = "iceberg.mr.filter.expression";
+  static final String TABLE_SCHEMA = "iceberg.mr.table.schema";
+  static final String TABLE_PATH = "iceberg.mr.table.path";
+  static final String READ_SCHEMA = "iceberg.mr.read.schema";
+  static final String READ_SUPPORT = "iceberg.mr.read.support";
+
+  private transient Table table;
+  private transient List<InputSplit> splits;
+
+  public IcebergInputFormat() {
+  }
+
+  @Override
+  public List<InputSplit> getSplits(JobContext context) {
+    if (splits != null) {
+      LOG.info("Returning cached splits: {}", splits.size());
+      return splits;
+    }
+
+    Configuration conf = context.getConfiguration();
+    table = getTable(conf);
+    TableScan scan = table.newScan();
+    //TODO add caseSensitive, snapshot id etc..
+
+    Expression filterExpression = 
SerializationUtil.deserializeFromBase64(conf.get(FILTER_EXPRESSION));
+    if (filterExpression != null) {
+      scan = scan.filter(filterExpression);
+    }
+
+    final String schemaStr = conf.get(READ_SCHEMA);
+    if (schemaStr != null) {
+      // Not sure if this is having any effect?
+      scan.project(SchemaParser.fromJson(schemaStr));
 
 Review comment:
   The base scan will combine the requested columns with the ones used by row 
filters to produce the required schema. If you don't intend to use that, then 
it isn't needed. But you could add the schema to the splits to know what to 
project.
   
   See 
https://github.com/apache/incubator-iceberg/blob/master/core/src/main/java/org/apache/iceberg/BaseTableScan.java#L298

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