[PARQUET-1217] Incorrect handling of missing values in Statistics

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.5.0, 1.6.0, 1.7.0, 1.8.0, 1.9.0, 1.10.0
• Fix Version/s: 1.10.0, 1.8.3
• Assignee: Gabor Szadovszky
• Reporter: Gabor Szadovszky
• Created: 15/Feb/18 14:59
• Updated: 23/Jun/24 03:30
• Resolved: 27/Feb/18 13:21

Description

As per the parquet-format specs the min/max values in statistics are optional. Therefore, it is possible to have numNulls in Statistics while we don't have min/max values. In StatisticsFilter we rely on the method StatisticsFilter.isAllNulls(ColumnChunkMetaData) to handle the case of null min/max values which is not correct due to the described scenario.
We shall check Statistics.hasNonNullValue() any time before using the actual min/max values.

In addition we don't check if the null_count is set or not when reading from the parquet file. We simply use the value which is 0 in case of unset. In the parquet-mr side the Statistics object uses the value 0 to sign that the num_nulls is unset. It is incorrect if we are searching for null values and we falsely drop a column chunk thinking there are no null values but the field in the statistics was simply unset.

Issue Links

• blocks: PARQUET-1277 Release Parquet-mr 1.8.3
• causes: SPARK-23852 Parquet MR bug can lead to incorrect SQL results
• links to: GitHub Pull Request #465
• links to: PR