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Keith Turner commented on ACCUMULO-2827: ---------------------------------------- I ran the test against 1.5.2-SNAPSHOT > 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-compaction-performance-test.patch, > 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. -- This message was sent by Atlassian JIRA (v6.2#6252)