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From "Keith Turner (JIRA)" <>
Subject [jira] [Created] (ACCUMULO-4011) Allow combiners reduce to return null
Date Fri, 25 Sep 2015 15:26:04 GMT
Keith Turner created ACCUMULO-4011:

             Summary: Allow combiners reduce to return null
                 Key: ACCUMULO-4011
             Project: Accumulo
          Issue Type: Improvement
            Reporter: Keith Turner
             Fix For: 1.8.0

Opening based on discussion from [PR 47|].  If the
reduce function in a combiner could return null to indicate that data should be dropped, this
could offer a solution to ACCUMULO-2232.

For example assume someone was using a summing combiner and wanted to delete a column with
a current value of 18.  They could insert -18.  If the combiner returned null when everything
summed to 0, this would delete the row col.  This method of deleting data would safe during
partial compactions and would work correctly with new data being inserted after the -18 was

If this done, needs to be done in a way that is compatible with existing combiners.

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