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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-10625) Remove unnecessary key compare from AbstractScannerV2.reseekTo
Date Thu, 27 Feb 2014 04:52:23 GMT
Lars Hofhansl created HBASE-10625:
-------------------------------------

             Summary: Remove unnecessary key compare from AbstractScannerV2.reseekTo
                 Key: HBASE-10625
                 URL: https://issues.apache.org/jira/browse/HBASE-10625
             Project: HBase
          Issue Type: Bug
            Reporter: Lars Hofhansl
         Attachments: 10625-0.94.txt

In reseekTo we find this
{code}
...
        compared = compareKey(reader.getComparator(), key, offset, length);
        if (compared < 1) {
          // If the required key is less than or equal to current key, then
          // don't do anything.
          return compared;
        } else {
           ...
           return loadBlockAndSeekToKey(this.block, this.nextIndexedKey,
              false, key, offset, length, false);
...
{code}
loadBlockAndSeekToKey already does the right thing when a we pass a key that sorts before
the current key. It's less efficient than this early check, but in the vast (all?) cases we
pass forward keys (as required by the reseek contract). We're optimizing the wrong thing.

Scanning with the ExplicitColumnTracker is 20-30% faster.
(I tested with rows of 5 short KVs selected the 2nd and or 4th column)

I propose simply removing that check.



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