[jira] [Created] (DRILL-4349) parquet reader returns wrong results when reading a nullable column that starts with a large number of nulls (>30k)

["Deneche A. Hakim (JIRA)" <ji...@apache.org>]

Deneche A. Hakim created DRILL-4349:
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             Summary: parquet reader returns wrong results when reading a nullable column that starts with a large number of nulls (>30k)
                 Key: DRILL-4349
                 URL: https://issues.apache.org/jira/browse/DRILL-4349
             Project: Apache Drill
          Issue Type: Bug
          Components: Storage - Parquet
    Affects Versions: 1.4.0
            Reporter: Deneche A. Hakim
            Assignee: Deneche A. Hakim
            Priority: Critical
             Fix For: 1.6.0


While reading a nullable column, if in a single pass we only read null values, the parquet reader resets the value of pageReader.readPosInBytes which will lead to wrong data read from the file.

To reproduce the issue, create a csv file (repro.csv) with 2 columns (id, val) with 50100 rows, where id equals to the row number and val is empty for the first 50k rows, and equal to id for the remaining rows.

create a parquet table from the csv file:
{noformat}
CREATE TABLE `repro_parquet` AS SELECT CAST(columns[0] AS INT) AS id, CAST(NULLIF(columns[1], '') AS DOUBLE) AS val from `repro.csv`;
{noformat}

Now if you query any of the non null values you will get wrong results:
{noformat}
0: jdbc:drill:zk=local> select * from `repro_parquet` where id>=50000 limit 10;
+--------+---------------------------+
|   id   |            val            |
+--------+---------------------------+
| 50000  | 9.11337776337441E-309     |
| 50001  | 3.26044E-319              |
| 50002  | 1.4916681476489723E-154   |
| 50003  | 2.0000000018890676        |
| 50004  | 2.681561588521345E154     |
| 50005  | -2.1016574E-317           |
| 50006  | -1.4916681476489723E-154  |
| 50007  | -2.0000000018890676       |
| 50008  | -2.681561588521345E154    |
| 50009  | 2.1016574E-317            |
+--------+---------------------------+
10 rows selected (0.238 seconds)
{noformat}

and here are the expected values:
{noformat}
0: jdbc:drill:zk=local> select * from `repro.csv` where cast(columns[0] as int)>=50000 limit 10;
+--------------------+
|      columns       |
+--------------------+
| ["50000","50000"]  |
| ["50001","50001"]  |
| ["50002","50002"]  |
| ["50003","50003"]  |
| ["50004","50004"]  |
| ["50005","50005"]  |
| ["50006","50006"]  |
| ["50007","50007"]  |
| ["50008","50008"]  |
| ["50009","50009"]  |
+--------------------+
{noformat}

I confirmed that the file is written correctly and the issue is in the parquet reader (already have a fix for it)



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