Re: Less allocated objects on each request

[James Tucker <jftucker@gmail.com>]

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Yeah, I've refused a previous patch on related grounds - this should be a
language implementation target. I'm glad to hear that reached patches.

Previously, back in the 1.8 days, I benched the aforementioned patch and it
was slower than allocating the strings. It turns out that a simple Rack
app, when you bench, will happily free these objects and not suffer major
problems under high load with the allocations. If I remember correctly the
prior patch added constant and method lookup time due to adding hierarchy
too.

On Fri, Oct 3, 2014 at 1:08 PM, Eric Wong <e@80x24.org> wrote:

> Hi all, this is about a recent rack.git commit:
> dc53a8c26dc55d21240233b3d83d36efdef6e924
>
> I don't disagree with this commit at this time, but I hope much of
> it will become unnecessary as older versions of Ruby get phased out.
>
> Since Ruby 2.1.0, constant string keys are deduplicated in hash
> literals.  Thus the following reuses the same "key" string in every
> case:
>
>         { "key" => val }
>         # ref: r44058
>
> Ruby 2.2 (coming December 2014) will also deduplicate the "key" literal
> allocation for lookups and assignment on regular hashes:
>
>         regular_hash["key"]         # opt_aref_with (in insns.def)
>         regular_hash["key"] = val   # opt_aset_with
>
> This speeds up the Rack env hash, but unfortunately won't help with
> Rack::Utils::HeaderHash :<
> (ref: r44551 + a few subsequent bugfixes)
>
> We originally planned to support dedupe for all strings (not just
> literals), but that caused performance regressions :<
>
> On a related note, Ruby 2.2 will also use power-of-two sized hash
> tables, speeding up lookups/assignments a little
> (~10-20%, CPU-dependent) for String keys [Feature #9425]
>
> This only applies to mainline Ruby, I am not up-to-date with
> Rubinius/JRuby internals.
>
> Thanks for reading!
>
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