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https://issues.apache.org/jira/browse/DRILL-5833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16189353#comment-16189353
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Paul Rogers commented on DRILL-5833:
------------------------------------
In order to avoid other random issues, the {{{TestParquetWriter}} test was
fixed to always put session parameters back to their default values (to reset
them) rather than setting them to some static value (which may have been the
default at one time, but is no longer.)
> 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 against the "old" Parquet reader.
> Because the {{store.parquet.use_new_reader}} was left at a previous value,
> sometimes the test would run against the "new" reader (and succeed) or
> against the "old" reader (and fail.)
> Once the test was forced to run against the "old" reader, 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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