[GitHub] [iceberg] jshmchenxi commented on a change in pull request #2577: Spark: Add read.locality.enabled to TableProperties to support disabl…

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jshmchenxi commented on a change in pull request #2577:
URL: https://github.com/apache/iceberg/pull/2577#discussion_r636788729



##########
File path: spark2/src/main/java/org/apache/iceberg/spark/source/Reader.java
##########
@@ -227,15 +233,58 @@ public StructType readSchema() {
     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));
-    }
+
+    initializeReadTasks(readTasks, tableBroadcast, expectedSchemaString, () -> InternalRowReaderFactory.INSTANCE);
 
     return readTasks;
   }
 
+  /**
+   * Initialize ReadTasks with multi threads as get block locations can be slow
+   *
+   * @param readTasks Result list to return
+   */
+  private <T> void initializeReadTasks(List<InputPartition<T>> readTasks,
+      Broadcast<Table> tableBroadcast, String expectedSchemaString, Supplier<ReaderFactory<T>> supplier) {
+    int taskInitThreads = Math.max(1, PropertyUtil.propertyAsInt(table.properties(), LOCALITY_TASK_INITIALIZE_THREADS,
+        LOCALITY_TASK_INITIALIZE_THREADS_DEFAULT));
+
+    if (!localityPreferred || taskInitThreads == 1) {
+      for (CombinedScanTask task : tasks()) {
+        readTasks.add(new ReadTask<>(
+            task, tableBroadcast, expectedSchemaString, caseSensitive,
+            localityPreferred, supplier.get()));
+      }
+      return;
+    }
+
+    List<Future<ReadTask<T>>> futures = new ArrayList<>();
+
+    final ExecutorService pool = Executors.newFixedThreadPool(
+        taskInitThreads,
+        new ThreadFactoryBuilder()
+            .setDaemon(true)
+            .setNameFormat("Init-ReadTask-%d")
+            .build());
+
+    List<CombinedScanTask> scanTasks = tasks();
+    for (int i = 0; i < scanTasks.size(); i++) {
+      final int curIndex = i;
+      futures.add(pool.submit(() -> new ReadTask<>(scanTasks.get(curIndex), tableBroadcast,
+          expectedSchemaString, caseSensitive, true, supplier.get())));
+    }

Review comment:
       Thanks! I will try to use iceberg utils in another PR and this will focus on adding the ability to disable locality.




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