From: Eric Wong <normalperson@...>
Date: 2015-12-12T03:21:44+00:00
Subject: [ruby-core:72073] Re: [Ruby trunk - Feature #11405] [PATCH] hash.c: minor speedups to int/fixnum keys

mame@ruby-lang.org wrote:
> Eric Wong wrote:
> >  Perhaps teach developers to rehash explicitly.  Maybe Hash#freeze
> >  can imply rehash, too.  But yes, I worry about memory increase more
> >  than speed nowadays.
> 
> I'm not sure if explicit/implicit rehasing will solve any issue.
> 
> The problem is that the linked lists are too(?) long.  Long linked
> lists decrease the average access speed, and also makes per-element
> access speed non-uniform.  Rehasing will not improve the average
> speed, nor eliminate/relax the inequality.

But wasn't the goal of adding rehash in r53031 to improve speed and
relax the inequality?

> It will just make us
> impossible to predict which element is fast to access and which is
> slow.  Will this make us happy?

I mean we may take freeze as a hint from the user to optimize the hash.

Perhaps we may rearrange data in contiguous memory for improved locality
(like "git repack" or defragmenting a filesystem).  I doubt we can have
a compacting GC at this point, but small-scale, explicit compaction
might still work.