[jira] [Created] (DRILL-5833) Parquet reader fails with assertion error for Decimal9, Decimal18 types

["Paul Rogers (JIRA)" <ji...@apache.org>]

Paul Rogers created DRILL-5833:
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             Summary: Parquet reader fails with assertion error for Decimal9, Decimal18 types
                 Key: DRILL-5833
                 URL: https://issues.apache.org/jira/browse/DRILL-5833
             Project: Apache Drill
          Issue Type: Bug
    Affects Versions: 1.10.0
            Reporter: Paul Rogers
            Assignee: Paul Rogers
             Fix For: 1.12.0


The {{TestParquetWriter.testDecimal()}} test recently failed. As it turns out, this test never ran properly before. Due to some bug, the CTAS that was supposed to write the file instead wrote an empty file, and the verification results were also empty. For some reason, the results are empty when the test is run stand-alone, but contains data when run as part of the test suite.

Once the test runs properly, it fails deep in the Parquet record reader in {{DrillParquetGroupConverter.getConverterForType()}}.

The code attempts to create a Decimal9 writer by calling {{SingleMapWriter.decimal9(String name)}} to create the writer. However, the code in this method says:

{code}
  public Decimal9Writer decimal9(String name) {
    // returns existing writer
    final FieldWriter writer = fields.get(name.toLowerCase());
    assert writer != null;
    return writer;
  }
{code}

And, indeed, the assertion is triggered.

As it turns out, the code for Decimal28 shows the proper solution:

{code}
mapWriter.decimal28Sparse(name, metadata.getScale(), metadata.getPrecision())
{code}

That is, pass the scale and precision to this form of the method which actually creates the writer:

{code}
  public Decimal9Writer decimal9(String name, int scale, int precision) {
{code}

Applying the same pattern to for the Parquet Decimal9 and Decimal18 types allows the above test to get past the asserts. Given this error, it is clear that this test could never have run, and so the error in the Parquet reader was never detected.

It also turns out that the test itself is wrong, reversing the validation and test queries:

{code}
  public void runTestAndValidate(String selection, String validationSelection, String inputTable, String outputFile) throws Exception {
    try {
      deleteTableIfExists(outputFile);
      ...
      // Query reads from the input (JSON) table
      String query = String.format("SELECT %s FROM %s", selection, inputTable);
      String create = "CREATE TABLE " + outputFile + " AS " + query;
      // validate query reads from the output (Parquet) table
      String validateQuery = String.format("SELECT %s FROM " + outputFile, validationSelection);
      test(create);

      testBuilder()
          .unOrdered()
          .sqlQuery(query) // Query under test is input query
          .sqlBaselineQuery(validateQuery) // Baseline query is output query
          .go();
{code}

Given this, it is the Parquet data that is wrong, not the baseline.



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