HashMap collision speed (regression 7->8)

[Chris Hegarty]

On 14/01/15 15:50, Peter Levart wrote:
> Hi,
>
> Loosely related to this topic, there is some local variable caching of
> comparableClassFor() result already being performed inside
> iterative/recursive methods of TreeNode, but this caching is just
> positive caching, meaning that null return is not cached. For keys that
> happen to implement Comparable, but are not simple-self-comparable
> (their class is not of the form: class C implements Comparable<C>),
> reflection is invoked each time comparison of the search key with Node
> key is attempted. This can be improved:
>
> http://cr.openjdk.java.net/~plevart/jdk9-dev/HM.comparableClassFor/InCallNegativeCache/webrev.01/

This seems like a good change.

-Chris


> Using modified version of Bernd's benchmark (adding 3rd variant of keys
> - FalseComp):
>
> http://cr.openjdk.java.net/~plevart/jdk9-dev/HM.comparableClassFor/InCallNegativeCache/HashMapCollision.java
>
>
> ...and and only running for badHash shows almost 25% improvement for
> FalseComp keys (skipping reflection invocations) and barely measurable
> improvement for NoComp keys (skipping instanceof checks), while Comp
> keys are not affected.
>
> Original JDK9 HashMap:
>
> Benchmark                                (initialSize)  Mode Samples
> Score     Error  Units
> j.t.HashMapCollision.badDistFalseComp               16    ss 20 4221.438
> +- 250.774     ms
> j.t.HashMapCollision.badDistNoComp                  16    ss 20 2868.605
> +-  40.754     ms
> j.t.HashMapCollision.badDistWithComp                16    ss 20 3030.780
> +- 111.315     ms
>
> Patched:
>
> Benchmark                                (initialSize)  Mode Samples
> Score     Error  Units
> j.t.HashMapCollision.badDistFalseComp               16    ss 20 3237.953
> +- 143.608     ms
> j.t.HashMapCollision.badDistNoComp                  16    ss 20 2643.024
> +- 137.067     ms
> j.t.HashMapCollision.badDistWithComp                16    ss 20 3087.902
> +- 122.041     ms
>
>
>
> Regards, Peter
>