[jira] [Created] (ORC-848) Recycle Internal Buffer in StringHashTableDictionary

["David Mollitor (Jira)" <ji...@apache.org>]

David Mollitor created ORC-848:
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             Summary: Recycle Internal Buffer in StringHashTableDictionary
                 Key: ORC-848
                 URL: https://issues.apache.org/jira/browse/ORC-848
             Project: ORC
          Issue Type: Improvement
            Reporter: David Mollitor
            Assignee: David Mollitor


{code:java|title=StringHashTableDictionary.java}
  private void initHashBuckets(int capacity) {
    DynamicIntArray[] buckets = new DynamicIntArray[capacity];
    for (int i = 0; i < capacity; i++) {
      // We don't need large bucket: If we have more than a handful of collisions,
      // then the table is too small or the function isn't good.
      buckets[i] = createBucket();
    }
    hashBuckets = buckets;
  }
{code}

This code was highlighted for me in a JMH run of the perf test.  The {{Dictionary}} is regularly cleared out and is reset back to its default state.  I'm sure most of the time is spent generating {{capacity}} buckets (buffers), but we can save one buffer initialization by only creating {{buckets}} if the capacity is different than requested (which is not the case with a {{clear()}}}).



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