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https://issues.apache.org/jira/browse/ACCUMULO-4468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15511154#comment-15511154
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Will Murnane commented on ACCUMULO-4468:
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Responding to [~ctubbsii]'s points first:
# Most things in Accumulo are dealt with in sorted order, so I think it's
reasonable to optimize for the case where things are sorted. Whether this is
true in the general case is a function of how one calls the function, but it's
not a change to the functionality of the code, just its performance. All the
places I can see it used in Accumulo, the keys that are being compared are
coming from SortedKeyValueIterator, so it's reasonable that we're comparing
keys which are sorted, and the new behavior will be an improvement.
# I ran some tests with JMH to see what the difference is like. I can post the
whole project, but here are some selected results. There are three functions
being compared. I implemented a subclass of Key which has new methods: my
proposed equals() function is called customWill, the original equals() copied
to the new class is called customVanilla, and the original equals() in the
original Key class is called standardEquals. The numbers to compare are really
the two custom* ones; the standardEquals value is given just to show that it's
in the same ballpark. \\ The test data set is generated before the benchmark
begins, and contains 1m keys to go through, calling previous.equals(next,
ROW_COLFAM). This is a worst-case scenario for sorted input, because the most
that it can manage to avoid doing (as compared to the current implementation)
is comparing the row values.
## I generated rows whose rowID are all equal, and the column family changes
every key.
{noformat}
Benchmark Mode Cnt Score Error Units
MyBenchmark.customVanilla thrpt 30 46.320 ± 3.803 ops/s
MyBenchmark.customWill thrpt 30 88.349 ± 2.723 ops/s
MyBenchmark.standardEquals thrpt 30 36.736 ± 0.883 ops/s
{noformat}
## I generated rows whose rowID are all equal, and the column family changes
every 3 keys.
{noformat}
Benchmark Mode Cnt Score Error Units
MyBenchmark.customVanilla thrpt 30 30.684 ± 1.258 ops/s
MyBenchmark.customWill thrpt 30 34.292 ± 1.339 ops/s
MyBenchmark.standardEquals thrpt 30 27.277 ± 0.984 ops/s
{noformat}
## I generated keys whose rowID are all equal, and the column family changes
every 5 keys.
{noformat}
Benchmark Mode Cnt Score Error Units
MyBenchmark.customVanilla thrpt 30 27.195 ± 0.895 ops/s
MyBenchmark.customWill thrpt 30 30.048 ± 0.838 ops/s
MyBenchmark.standardEquals thrpt 30 25.044 ± 0.731 ops/s
{noformat}
## Finally, I generated keys whose rowID are all equal, and the column family
changes every 1000 keys.
{noformat}
Benchmark Mode Cnt Score Error Units
MyBenchmark.customVanilla thrpt 30 23.447 ± 1.010 ops/s
MyBenchmark.customWill thrpt 30 23.427 ± 0.371 ops/s
MyBenchmark.standardEquals thrpt 30 22.356 ± 0.192 ops/s
{noformat}
# As a user of the API, I'd rather not have to think about equalsForward()
versus equalsBackward(). Maybe add an optional flag to specify direction of
comparison, for
# I agree in general, but I would argue that the code of the current equals()
method is messier and harder to read. It repeats the same code quite a bit. I
wrote a comment in the patch remarking on the fact that there's fallthrough and
it's used intentionally, to try to prevent future confusion.
[~elserj] I agree that any change should start with prejudice against it.
However, I think the numbers above prove my case: when keys are presented in
sorted order, which happens often in Accumulo, the proposed method of comparing
is slightly but noticeably faster. The degree of improvement depends on the
data, but it doesn't perform worse than the current solution in any case that I
tested.
> accumulo.core.data.Key.equals(Key, PartialKey) improvement
> ----------------------------------------------------------
>
> Key: ACCUMULO-4468
> URL: https://issues.apache.org/jira/browse/ACCUMULO-4468
> Project: Accumulo
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.8.0
> Reporter: Will Murnane
> Priority: Trivial
> Labels: newbie, performance
> Attachments: key_comparison.patch
>
>
> In the Key.equals(Key, PartialKey) overload, the current method compares
> starting at the beginning of the key, and works its way toward the end. This
> functions correctly, of course, but one of the typical uses of this method is
> to compare adjacent rows to break them into larger chunks. For example,
> accumulo.core.iterators.Combiner repeatedly calls this method with subsequent
> pairs of keys.
> I have a patch which reverses the comparison order. That is, if the method is
> called with ROW_COLFAM_COLQUAL_COLVIS, it will compare visibility, cq, cf,
> and finally row. This (marginally) improves the speed of comparisons in the
> relatively common case where only the last part is changing, with less
> complex code.
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