[GitHub] [orc] belugabehr commented on pull request #743: ORC-834: Do Not Convert to String in DecimalFromTimestampTreeReader

[GitBox <gi...@apache.org>]

belugabehr commented on pull request #743:
URL: https://github.com/apache/orc/pull/743#issuecomment-877200933


   A quick test (hardly definitive, but indicative) shows an order of magnitude performance improvement:
   
   ```java
       long t1 = System.nanoTime();
       long r = 0;
       for (long i = -100_000L; i < 100_000; i++) {
         BigDecimal secondsBd = new BigDecimal(i);
         BigDecimal nanosBd = new BigDecimal(i).movePointLeft(9);
         BigDecimal resultBd = (i >= 0L) ? secondsBd.add(nanosBd) : secondsBd.subtract(nanosBd);
         r += resultBd.longValue();
       }
       long t2 = System.nanoTime();
   
       System.out.println(r);
       System.out.println(t2 - t1);
   ```
   
   This can be done even faster by more fully utilizing the Hive BigDecimalWritable stuff, but this is a good start.


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