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From "Matthew F. Dennis (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-4894) log number of combined/merged rows during a compaction
Date Thu, 01 Nov 2012 19:15:13 GMT
Matthew F. Dennis created CASSANDRA-4894:

             Summary: log number of combined/merged rows during a compaction
                 Key: CASSANDRA-4894
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Matthew F. Dennis
            Priority: Critical

we already log some details about compactions but it would be useful to know how many rows
were merged (resulting in "useful" work) and how many were unique (representing "wasted work").

the simple approach requires two additional counters (one for unique rows, one for merged
rows).  As the merge join is progressing if two rows are combined, tick the joined counter.
 If a row is simply copied tick the unique counter.

a more complete solution would be to keep a separate count for each number of merges.  This
would require number_of_files_being_merged counters.  If no rows were merged, tick counters[0],
if two rows were merged tick counters[1] and so on 

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