[GitHub] drill pull request #600: DRILL-4373: Drill and Hive have incompatible timest...

[bitblender <gi...@git.apache.org>]

Github user bitblender commented on a diff in the pull request:

    https://github.com/apache/drill/pull/600#discussion_r82314071
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetReaderUtility.java ---
    @@ -45,4 +53,34 @@ public static int getIntFromLEBytes(byte[] input, int start) {
         }
         return out;
       }
    +
    +  /**
    +   * Utilities for converting from parquet INT96 binary (impala, hive timestamp)
    +   * to date time value. This utilizes the Joda library.
    +   */
    +  public static class NanoTimeUtils {
    +
    +    public static final long NANOS_PER_DAY = TimeUnit.DAYS.toNanos(1);
    +    public static final long NANOS_PER_HOUR = TimeUnit.HOURS.toNanos(1);
    +    public static final long NANOS_PER_MINUTE = TimeUnit.MINUTES.toNanos(1);
    +    public static final long NANOS_PER_SECOND = TimeUnit.SECONDS.toNanos(1);
    +    public static final long NANOS_PER_MILLISECOND =  TimeUnit.MILLISECONDS.toNanos(1);
    +
    +  /**
    +   * @param binaryTimeStampValue
    +   *          hive, impala timestamp values with nanoseconds precision
    +   *          are stored in parquet Binary as INT96
    +   *
    +   * @return  the number of milliseconds since January 1, 1970, 00:00:00 GMT
    +   *          represented by @param binaryTimeStampValue .
    +   */
    +    public static long getDateTimeValueFromBinary(Binary binaryTimeStampValue) {
    +      NanoTime nt = NanoTime.fromBinary(binaryTimeStampValue);
    +      int julianDay = nt.getJulianDay();
    +      long nanosOfDay = nt.getTimeOfDayNanos();
    +      return DateTimeUtils.fromJulianDay(julianDay-0.5d) + nanosOfDay/NANOS_PER_MILLISECOND;
    --- End diff --
    
    1.  I would recommend not using Joda. Do the calculations directly, like in ConvertFromImpalaTimestamp. Joda uses non-standard, hence  confusing, terminology. What Joda calls and uses as JulianDay, is actually Julian Date. Seems like you have identified this discrepancy and adjusted for it by subtracting 0.5 from _julianDay_. 
    
        Note: (I guess you have already figured this out) : The actual code and the Joda code in the comment, in ConvertFromImpalaTimestamp, are inconsistent. Took me a day to figure out the reason behind this ! A bug should be opened to delete the comment. 
    
    2. Can you please also leave a comment stating that 2440588 is the JDN for the Unix Epoch.
    
    3. Please leave a comment stating that the order of the calls to get _julianDay_ and _nanosOfDay_ matters. You can do this by just stating how timestamps are stored in INT96 i.e 32-bit JDN followed by 64-bit nanosOfDay.
    
    4. Consistent(single or none) spacing for binary operators (+-/) used here would be nice. Single spacing would be preferable.


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