[GitHub] [spark] HyukjinKwon commented on a change in pull request #33006: [SPARK-35846][SQL] Introduce ParquetReadState to track various states while reading a Parquet column chunk

[GitBox <gi...@apache.org>]

HyukjinKwon commented on a change in pull request #33006:
URL: https://github.com/apache/spark/pull/33006#discussion_r655847305



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File path: sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/VectorizedColumnReader.java
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@@ -174,24 +162,29 @@ void readBatch(int total, WritableColumnVector column) throws IOException {
       // page.
       dictionaryIds = column.reserveDictionaryIds(total);
     }
-    while (total > 0) {
+    readState.resetForBatch(total);
+    while (readState.valuesToReadInBatch > 0) {
       // Compute the number of values we want to read in this page.
-      int leftInPage = (int) (endOfPageValueCount - valuesRead);
-      if (leftInPage == 0) {
+      if (readState.valuesToReadInPage == 0) {
         readPage();
-        leftInPage = (int) (endOfPageValueCount - valuesRead);
+        readState.resetForPage(pageValueCount);
       }
-      int num = Math.min(total, leftInPage);
       PrimitiveType.PrimitiveTypeName typeName =
           descriptor.getPrimitiveType().getPrimitiveTypeName();
       if (isCurrentPageDictionaryEncoded) {
+        boolean supportLazyDecoding = readState.offset == 0 &&
+          isLazyDecodingSupported(typeName);
+
+        // Save starting offset in case we need to decode dictionary IDs.
+        int startOffset = readState.offset;
+
         // Read and decode dictionary ids.
-        defColumn.readIntegers(
-            num, dictionaryIds, column, rowId, maxDefLevel, (VectorizedValuesReader) dataColumn);
+        defColumn.readIntegers(readState, dictionaryIds, column,
+          (VectorizedValuesReader) dataColumn);
 
         // TIMESTAMP_MILLIS encoded as INT64 can't be lazily decoded as we need to post process
         // the values to add microseconds precision.
-        if (column.hasDictionary() || (rowId == 0 && isLazyDecodingSupported(typeName))) {
+        if (column.hasDictionary() || supportLazyDecoding) {

Review comment:
       Just to make sure we don't miss anything, there's a small side effect here. Previously `(rowId == 0 && isLazyDecodingSupported(typeName))` wasn't executed when `column.hasDictionary()` true, but now it's executed alway.




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