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From "Adam Fuchs (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ACCUMULO-1696) deep copy in the compaction scope iterators can throw off the stats
Date Fri, 06 Sep 2013 17:57:51 GMT
Adam Fuchs created ACCUMULO-1696:
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             Summary: deep copy in the compaction scope iterators can throw off the stats
                 Key: ACCUMULO-1696
                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1696
             Project: Accumulo
          Issue Type: Bug
          Components: tserver
    Affects Versions: 1.5.0
            Reporter: Adam Fuchs
            Priority: Minor


When application-level iterators deep copy the source iterator in a major compaction, the
stats can be significantly off. We count two things in a major compaction:
1. Entries read. This is done using a counting iterator sitting just above the system iterators.
2. Entries written. This is done by counting the entries that are written to the RFile.
Here's an example of what we see in the Accumulo logs:
{code}
2013-09-06 11:53:31,371 [tabletserver.Compactor] DEBUG: Compaction k;row11;row10 20 read |
382,629 written |      3 entries/sec |  5.337 secs
{code}
In this case, we're only counting 20 entries read, presumably because the iterators have been
deep copied and the counting iterator that is being polled does not get a complete view of
how many entries were read. Instead of 3 entries/sec we should have registered close to 72k
entries/sec.

To fix this, should we be counting all reads coming from any of the deep copies of the source
iterators? This could be done by using a CountingIterator that keeps one counter for all deep
copies. Thread-level counters could be used for lock-free counts in case multiple threads
are ever used.

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