PARQUET-1217: Incorrect handling of missing values in Statistics by gszadovszky · Pull Request #458 · apache/parquet-java

gszadovszky · 2018-02-19T12:30:31Z

In parquet-format every value in Statistics is optional while parquet-mr does not properly handle these scenarios:

null_count is set but min/max or min_value/max_value are not: filtering may fail with NPE or incorrect filtering occurs
fix: check if min/max is set before comparing to the related values
null_count is not set: filtering handles null_count as if it would be 0 -> incorrect filtering may occur
fix: introduce new method in Statistics object to check if num_nulls is set; check if num_nulls is set by the new method before using its value for filtering

zivanfi

LGTM, thanks.

@rdblue, would you also take a look if your time allows? Thanks.

zivanfi · 2018-02-19T13:29:10Z

    }

-    if (hasNulls(meta)) {
+    if (stats.isNumNullsSet() && hasNulls(meta)) {


(optional) You might consider adding the "stats.isNumNullsSet()" clause to the body of hasNulls() itself, but I don't really have a strong opinion on this.

It would not work correctly because hasNulls is called negated as well.

zivanfi · 2018-02-19T13:42:27Z

      (String createdBy, Statistics formatStats, PrimitiveType type, SortOrder typeSortOrder) {
    // create stats object based on the column type
-    org.apache.parquet.column.statistics.Statistics stats = org.apache.parquet.column.statistics.Statistics.createStats(type);
+    StatisticsBuilder builder = org.apache.parquet.column.statistics.Statistics.getBuilder(type);


(optional, nit): I think stats would be more descriptive regarding the purpose of this variable, even if it is a builder. Alternatively, statsBuilder.

zivanfi · 2018-02-19T13:44:42Z


  private static final IntStatistics intStats = new IntStatistics();
  private static final IntStatistics nullIntStats = new IntStatistics();
+  private static final org.apache.parquet.column.statistics.Statistics<?> missingMinMaxIntStats = org.apache.parquet.column.statistics.Statistics


Not only man and max are missing from this one, but numNulls as well. Would missingIntStats be a better name? Alternatively, set numNulls.

zivanfi · 2018-02-19T13:48:16Z

      getDoubleColumnMeta(doubleStats, 177L));

+  private static final List<ColumnChunkMetaData> missingMinMaxColumnMetas = Arrays.asList(
+      getIntColumnMeta(missingMinMaxIntStats, 177L),        // missing min/max, no null values => stats is empty


Please clarify: Is it really the lack of null values or the lack of numNulls?

zivanfi · 2018-02-19T13:49:45Z

+  public static class AllPositiveUdp extends UserDefinedPredicate<Double> {
+    @Override
+    public boolean keep(Double value) {
+      if (value == null) {


Should/could this be an assert instead?

It is more an UDP implementation for testing purposes than the test itself. In addition, we have to return a boolean even if an assertion is added.

zivanfi · 2018-02-19T13:52:22Z

-    w.writeDataPage(2, 4, BytesInput.from(BYTES2), STATS2, BIT_PACKED, BIT_PACKED, PLAIN);
-    w.writeDataPage(3, 4, BytesInput.from(BYTES2), STATS2, BIT_PACKED, BIT_PACKED, PLAIN);
-    w.writeDataPage(1, 4, BytesInput.from(BYTES2), STATS2, BIT_PACKED, BIT_PACKED, PLAIN);
+    w.writeDataPage(2, 4, BytesInput.from(BYTES2), EMPTY_STATS, BIT_PACKED, BIT_PACKED, PLAIN);


I wonder what purpose STATS1 and STATS2 might have served in the original code.

I have no idea, why we had two Statistics objects for the same purpose. I think, it is more readable this way.

+1

I don't remember either.

rdblue · 2018-02-21T16:52:08Z

@gszadovszky, can you update the description with a summary of the problem and how this fixes it? It's easier to review a patch if I know the general idea behind it.

zivanfi · 2018-02-21T17:32:37Z

@rdblue, until Gabor updates the description, you can read about the error in the JIRA: https://issues.apache.org/jira/browse/PARQUET-1217

rdblue · 2018-02-21T19:44:24Z

Have any engines actually written stats with num_nulls set, min and max not set, and num_nulls != num_values? That's the case that this is fixing, right? I don't think Parquet MR will write any stats if min and max are not written.

rdblue · 2018-02-21T19:46:26Z

+  /**
+   * Builder class to build Statistics objects. Used to read the statistics from the Parquet file.
+   */
+  public static class StatisticsBuilder {


Why add this to the public API?

Because this is nested, it should be Statistics.Builder, not Statistics.StatisticsBuilder.

It needs to be public because ParquetMetadataConverter uses it. The concept is that you are only able to initialize num_nulls to -1 (meaning it is not set in the file) by using the builder (read path). If you are creating a new Statistics object in any other way (write path) num_nulls will be initialized to 0.
I'll rename it to Builder.

gszadovszky · 2018-02-22T07:43:17Z

Impala started to write the new min_value/max_value with num_nulls set. In the same CDH release we use a parquet-mr release where the handling of the new min_value/max_value is not backported therefore, we are seeing only unset min and max values with set num_nulls.
In addition, there was an Impala release where no num_nulls were written which is correct from the parquet-format point-of-view but in parquet-mr we were handled unset num_nulls the same way as the num_nulls would be 0.

zivanfi

LGTM. @rdblue, are you okay with me merging this tomorrow? Thanks.

In parquet-format every value in Statistics is optional while parquet-mr does not properly handle these scenarios: - null_count is set but min/max or min_value/max_value are not: filtering may fail with NPE or incorrect filtering occurs fix: check if min/max is set before comparing to the related values - null_count is not set: filtering handles null_count as if it would be 0 -> incorrect filtering may occur fix: introduce new method in Statistics object to check if num_nulls is set; check if num_nulls is set by the new method before using its value for filtering Author: Gabor Szadovszky <gabor.szadovszky@cloudera.com> Closes apache#458 from gszadovszky/PARQUET-1217 and squashes the following commits: 9d14090 [Gabor Szadovszky] Updates according to rdblue's comments 116d1d3 [Gabor Szadovszky] PARQUET-1217: Updates according to zi's comments c264b50 [Gabor Szadovszky] PARQUET-1217: fix handling of unset nullCount 2ec2fb1 [Gabor Szadovszky] PARQUET-1217: Incorrect handling of missing values in Statistics

In parquet-format every value in Statistics is optional while parquet-mr does not properly handle these scenarios: - null_count is set but min/max or min_value/max_value are not: filtering may fail with NPE or incorrect filtering occurs fix: check if min/max is set before comparing to the related values - null_count is not set: filtering handles null_count as if it would be 0 -> incorrect filtering may occur fix: introduce new method in Statistics object to check if num_nulls is set; check if num_nulls is set by the new method before using its value for filtering Author: Gabor Szadovszky <gabor.szadovszky@cloudera.com> Closes apache#458 from gszadovszky/PARQUET-1217 and squashes the following commits: 9d14090 [Gabor Szadovszky] Updates according to rdblue's comments 116d1d3 [Gabor Szadovszky] PARQUET-1217: Updates according to zi's comments c264b50 [Gabor Szadovszky] PARQUET-1217: fix handling of unset nullCount 2ec2fb1 [Gabor Szadovszky] PARQUET-1217: Incorrect handling of missing values in Statistics This change is based on b82d962 but is not a clean cherry-pick.

In parquet-format every value in Statistics is optional while parquet-mr does not properly handle these scenarios: - null_count is set but min/max or min_value/max_value are not: filtering may fail with NPE or incorrect filtering occurs fix: check if min/max is set before comparing to the related values - null_count is not set: filtering handles null_count as if it would be 0 -> incorrect filtering may occur fix: introduce new method in Statistics object to check if num_nulls is set; check if num_nulls is set by the new method before using its value for filtering Author: Gabor Szadovszky <gabor.szadovszky@cloudera.com> Closes #458 from gszadovszky/PARQUET-1217 and squashes the following commits: 9d14090 [Gabor Szadovszky] Updates according to rdblue's comments 116d1d3 [Gabor Szadovszky] PARQUET-1217: Updates according to zi's comments c264b50 [Gabor Szadovszky] PARQUET-1217: fix handling of unset nullCount 2ec2fb1 [Gabor Szadovszky] PARQUET-1217: Incorrect handling of missing values in Statistics This change is based on b82d962 but is not a clean cherry-pick.

Gabor Szadovszky added 2 commits February 16, 2018 15:48

PARQUET-1217: Incorrect handling of missing values in Statistics

2ec2fb1

PARQUET-1217: fix handling of unset nullCount

c264b50

zivanfi approved these changes Feb 19, 2018

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PARQUET-1217: Updates according to zi's comments

116d1d3

rdblue reviewed Feb 21, 2018

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Updates according to rdblue's comments

9d14090

zivanfi approved these changes Feb 26, 2018

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asfgit closed this in b82d962 Feb 27, 2018

gszadovszky mentioned this pull request Apr 19, 2018

PARQUET-1217: Incorrect handling of missing values in Statistics #465

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takezoe mentioned this pull request May 25, 2024

Use Statistics.Builder instead of mutating Statistics in Parquet MetadataReader trinodb/trino#22136

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asfimport mentioned this pull request Jun 23, 2024

Incorrect handling of missing values in Statistics #2134

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rdblue commented Feb 21, 2018

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gszadovszky commented Feb 22, 2018

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gszadovszky commented Feb 19, 2018 •

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