[GitHub] [spark] sadikovi commented on a diff in pull request #37419: [SPARK-39833][SQL] Fix Parquet incorrect count issue when requiredSchema is empty and column index is enabled in DSv1

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

sadikovi commented on code in PR #37419:
URL: https://github.com/apache/spark/pull/37419#discussion_r938492838


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sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala:
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@@ -228,6 +228,13 @@ class ParquetFileFormat
       SQLConf.PARQUET_TIMESTAMP_NTZ_ENABLED.key,
       sparkSession.sessionState.conf.parquetTimestampNTZEnabled)
 
+    // See PARQUET-2170.
+    // Disable column index optimisation when required schema is empty so we get the correct
+    // row count from parquet-mr.
+    if (requiredSchema.isEmpty) {

Review Comment:
   No, this is not required for DSv2.
   
   The test works in DSv2 due to another inconsistency - Parquet DSv2 filters out the column in `readDataSchema`()` method due to the fact that both partition column and data column are similar in a case insensitive mode. The final schema becomes empty resulting in the empty list of filters and thus returning the correct number of records. It is rather a performance inefficiency in DSv2 as the entire file will be scanned. However, the result will be correct.



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