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Christopher Tubbs commented on ACCUMULO-4468:
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Hi [~wmurnane]. Thanks for the patch!
After reviewing, I had a few comments:
1. This may speed things up only if the probability of not being equal is
greater in the lower dimensions of the key than the higher ones. I'm not sure
this is the case, as I don't have a strong sense of when this method is called,
or how frequently. What analysis have you done to determine these relative
probabilities?
2. Have you run any experiments to determine the performance differences in
various use cases?
3. If this method is primarily used in user code, would a new method to compare
in reverse order be better, to account for both cases? Perhaps it'd be better
to optimize the Combiner code, rather than change the default behavior for all
cases?
4. I think relying on fall-through behavior in switch statements should be
avoided. It's prone to error, especially as code is refactored over time. I
think it's better to avoid it than to suppress the warning. This may be a style
choice, but it's a preference that the java compiler weighs in on (by making
fallthrough a default compiler warning), and I'd prefer to avoid behavior which
results in compiler warnings whenever possible.
> 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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