Add a doc comment and error message in ParquetPageSource

trinodb · Apr 9, 2021 · 1f3955a · 1f3955a
1 parent 5f3381f
commit 1f3955a
Showing 1 changed file with 5 additions and 1 deletion.
diff --git a/plugin/trino-hive/src/main/java/io/trino/plugin/hive/parquet/ParquetPageSource.java b/plugin/trino-hive/src/main/java/io/trino/plugin/hive/parquet/ParquetPageSource.java
@@ -142,6 +142,10 @@ public void close()
     private final class ParquetBlockLoader
             implements LazyBlockLoader
     {
+        /**
+         * Stores batch ID at instantiation time. Loading fails if the ID
+         * changes before {@link #load()} is called.
+         */
         private final int expectedBatchId = batchId;
         private final Field field;
         private boolean loaded;
@@ -155,7 +159,7 @@ public ParquetBlockLoader(Field field)
         public final Block load()
         {
             checkState(!loaded, "Already loaded");
-            checkState(batchId == expectedBatchId);
+            checkState(batchId == expectedBatchId, "Inconsistent state; wrong batch");
 
             Block block;
             String parquetDataSourceId = parquetReader.getDataSource().getId().toString();