[jira] [Created] (HBASE-10805) Speed up KeyValueHeap.next() a bit

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

Lars Hofhansl created HBASE-10805:
-------------------------------------

             Summary: Speed up KeyValueHeap.next() a bit
                 Key: HBASE-10805
                 URL: https://issues.apache.org/jira/browse/HBASE-10805
             Project: HBase
          Issue Type: Bug
            Reporter: Lars Hofhansl
             Fix For: 0.99.0, 0.94.19, 0.98.2, 0.96.3


See discussion on HBASE-9969.
This was brought up by [~mcorgan]. Even though I didn't believe him first.
{code}
      KeyValueScanner topScanner = this.heap.peek();
      if (topScanner == null ||
          this.comparator.compare(kvNext, topScanner.peek()) >= 0) {
        this.heap.add(this.current);
        this.current = pollRealKV();
      }
{code}

We already have the invariant everywhere this.current always has a real KV polled. So adding current back to the heap followed by pollRealKV() is a no-op if this.current is the only scanner anyway.

This can be changed to:
{code}
      ...
      if (topScanner != null &&
          this.comparator.compare(kvNext, topScanner.peek()) >= 0) {
      ...
{code}

With 20m rows, 5 cols each, everything in the cache, fully compacted - i.e. one HFile per store, a scan that filters everything at the server through all 100m KVs takes 15.1s without the change and 13.3s with it, so a 12% improvement.




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