[GitHub] sachouche opened a new pull request #1630: DRILL-7018: Fixed Parquet buffer overflow when reading timestamp column

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sachouche opened a new pull request #1630: DRILL-7018: Fixed Parquet buffer overflow when reading timestamp column
URL: https://github.com/apache/drill/pull/1630
 
 
   **Problem Description**
   - Parquet advertises timestamps as a 12 bytes precision (INT96)
   - By default, such entries are mapped to a Drill VARBINARY data type
   When the "store.parquet.reader.int96_as_timestamp" option is set, then the Parquet reader will map this DT to a Drill data type but with less precision (8 bytes; nanoseconds will be lost)
   - The previous Drill code (before the batch sizing feature) used to pre-allocate buffers (initially) with at least 4096 values
   - The current parquet file has a timestamp column with 31 null values
   - The code attempts to advance the write offset to 31 * 12 (the original column precision); the correct precision is based for non-null values
   - The old Drill version will work since it had plenty of space pre-allocated
   - The batch sizing feature is smarter as it allocated the strict minimum: 31 * 8 bytes
   - Unfortunately, this uncovered the 1.10 bug where the INT96 precision was used instead of the Drill timestamp precision of 8 bytes
   - My guess, Drill 1.10 has the same issue for larger datasets
   
   **NOTE**
   - Setting the writer offset (when encountering null values) to an erroneous value is not leading to corruption
   - My guess is that setting the data uses a mutator which uses entry based indexing (since it is fixed length); thus, the index writer offset is not causing harm
   
   **FIX**
   - The fix is to modify the Parquet fixed reader code to use the Drill DT precision instead
   - Looking at the code, only the nullable fixed reader is affected with this bug

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