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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