[GitHub] [iceberg] ConeyLiu commented on a diff in pull request #7279: [Parquet] Eagerly fetch row groups when reading parquet

["ConeyLiu (via GitHub)" <gi...@apache.org>]

ConeyLiu commented on code in PR #7279:
URL: https://github.com/apache/iceberg/pull/7279#discussion_r1161572794


##########
parquet/src/main/java/org/apache/iceberg/parquet/VectorizedParquetReader.java:
##########
@@ -109,11 +117,23 @@ public CloseableIterator<T> iterator() {
     private final int batchSize;
     private final List<Map<ColumnPath, ColumnChunkMetaData>> columnChunkMetadata;
     private final boolean reuseContainers;
-    private int nextRowGroup = 0;
     private long nextRowGroupStart = 0;
     private long valuesRead = 0;
     private T last = null;
     private final long[] rowGroupsStartRowPos;
+    private final int totalRowGroups;
+    private static final ExecutorService prefetchService =
+        MoreExecutors.getExitingExecutorService(
+            (ThreadPoolExecutor)
+                Executors.newFixedThreadPool(
+                    4,

Review Comment:
   The `ThreadPool` should be shared by all the readers in the process. But the hard code may need to improve.



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