RFR (XS): CR 8006176: Switch to optimal identity hash code generator

[Aleksey Shipilev]

On 01/14/2013 04:53 PM, David Holmes wrote:
> This kind of switch can not be made lightly. It is not just a matter of
> raw performance, we have to understand how the change might affect
> existing applications. The default affects thousands of programs. A
> particular program can be run with -XX:hashCode=5 if it suits.

Agreed with the rationale; what should the appropriate test look like
for this kind of change?

Disagreed with the conclusion: on these grounds we might as well do not
change the default behavior at all, frightened about all these
applications relying on subtleties they were never guaranteed to be
upheld. Having this in mind, I would say we should use most-performant
version, and let users to fallback to -XX:hashCode=0 if they identify
the problem with the new setting, which should be the red flag for their
applications anyway.

-Aleksey.