kbendick commented on a change in pull request #2803:
URL: https://github.com/apache/iceberg/pull/2803#discussion_r667568889



##########
File path: spark2/src/main/java/org/apache/iceberg/spark/source/Reader.java
##########
@@ -205,35 +215,62 @@ public StructType readSchema() {
     // broadcast the table metadata as input partitions will be sent to 
executors
     Broadcast<Table> tableBroadcast = 
sparkContext.broadcast(SerializableTable.copyOf(table));
 
-    List<InputPartition<ColumnarBatch>> readTasks = Lists.newArrayList();
-    for (CombinedScanTask task : tasks()) {
-      readTasks.add(new ReadTask<>(
-          task, tableBroadcast, expectedSchemaString, caseSensitive,
-          localityPreferred, new BatchReaderFactory(batchSize)));
+    int taskSize = tasks().size();
+    InputPartition<ColumnarBatch>[] readTasks = new InputPartition[taskSize];
+    Long startTime = System.currentTimeMillis();
+    try {
+      pool.submit(() -> IntStream.range(0, taskSize).parallel()
+              .mapToObj(taskId -> {
+                LOG.trace("The size of scanTasks is {},  current taskId is {}, 
current thread id is {}",
+                        taskSize, taskId, Thread.currentThread().getName());
+                readTasks[taskId] = new ReadTask<>(
+                        tasks().get(taskId), tableBroadcast, 
expectedSchemaString, caseSensitive,
+                        localityPreferred, new BatchReaderFactory(batchSize));
+                return true;
+              }).collect(Collectors.toList())).get();
+    } catch (Exception e) {
+      e.printStackTrace();
+      System.exit(-1);
     }
-    LOG.info("Batching input partitions with {} tasks.", readTasks.size());
-
-    return readTasks;
+    Long endTime = System.currentTimeMillis();
+    LOG.info("Batching input partitions with {} tasks.", readTasks.length);
+    LOG.info("It took {} s to construct {} readTasks with localityPreferred = 
{}.", (endTime - startTime) / 1000,
+            taskSize, localityPreferred);
+    return Arrays.asList(readTasks.clone());
   }
 
   /**
    * This is called in the Spark Driver when data is to be materialized into 
{@link InternalRow}
    */
+  @SuppressWarnings({"checkstyle:LocalVariableName", 
"checkstyle:RegexpSinglelineJava"})
   @Override
   public List<InputPartition<InternalRow>> planInputPartitions() {
     String expectedSchemaString = SchemaParser.toJson(lazySchema());
 
     // broadcast the table metadata as input partitions will be sent to 
executors
     Broadcast<Table> tableBroadcast = 
sparkContext.broadcast(SerializableTable.copyOf(table));
-
-    List<InputPartition<InternalRow>> readTasks = Lists.newArrayList();
-    for (CombinedScanTask task : tasks()) {
-      readTasks.add(new ReadTask<>(
-          task, tableBroadcast, expectedSchemaString, caseSensitive,
-          localityPreferred, InternalRowReaderFactory.INSTANCE));
+    int taskSize = tasks().size();
+    InputPartition<InternalRow>[] readTasks = new InputPartition[taskSize];
+    Long start_time = System.currentTimeMillis();

Review comment:
       We don't use snake case (outside of the python code). This should be 
startTime.




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