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https://issues.apache.org/jira/browse/ACCUMULO-2827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14028137#comment-14028137
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Josh Elser commented on ACCUMULO-2827:
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Seems promising enough. I'm not sure how best to move forward with this though.
I guess we need to decide for certain if this is something we want to apply to
1.5 and 1.6 (performance gains are usually justifiable). Are those who are
interested here happy with the amount of testing that was done? If more testing
is desired, before or after this gets committed?
> HeapIterator optimization
> -------------------------
>
> Key: ACCUMULO-2827
> URL: https://issues.apache.org/jira/browse/ACCUMULO-2827
> Project: Accumulo
> Issue Type: Improvement
> Affects Versions: 1.5.1, 1.6.0
> Reporter: Jonathan Park
> Assignee: Jonathan Park
> Priority: Minor
> Fix For: 1.5.2, 1.6.1, 1.7.0
>
> Attachments: ACCUMULO-2827.0.patch.txt, accumulo-2827.raw_data,
> new_heapiter.png, old_heapiter.png, together.png
>
>
> We've been running a few performance tests of our iterator stack and noticed
> a decent amount of time spent in the HeapIterator specifically related to
> add/removal into the heap.
> This may not be a general enough optimization but we thought we'd see what
> people thought. Our assumption is that it's more probable that the current
> "top iterator" will supply the next value in the iteration than not. The
> current implementation takes the other assumption by always removing +
> inserting the minimum iterator back into the heap. With the implementation of
> a binary heap that we're using, this can get costly if our assumption is
> wrong because we pay the log penalty of percolating up the iterator in the
> heap upon insertion and again when percolating down upon removal.
> We believe our assumption is a fair one to hold given that as major
> compactions create a log distribution of file sizes, it's likely that we may
> see a long chain of consecutive entries coming from 1 iterator.
> Understandably, taking this assumption comes at an additional cost in the
> case that we're wrong. Therefore, we've run a few benchmarking tests to see
> how much of a cost we pay as well as what kind of benefit we see. I've
> attached a potential patch (which includes a test harness) + image that
> captures the results of our tests. The x-axis represents # of repeated keys
> before switching to another iterator. The y-axis represents iteration time.
> The sets of blue + red lines varies in # of iterators present in the heap.
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