Encourage `Hash#compare_by_identity`

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#189 2 comments 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
ruby
Domain
performance

Research direction

The issue names no repository file or test. Start by reproducing the supplied Ruby benchmark for ordinary and identity-comparison Hash lookups, then inspect the project’s existing benchmark conventions. Done would require a clearly scoped optimization target and benchmark evidence showing the intended improvement.

Written by the indexing model from the issue text.

Description

If one is using keys that can be compared by identity, and if those keys are not already optimized (symbols are optimized, not sure what else is), using compare_by_identity can yield a 4x speedup.

require 'benchmark/ips'

KEY = Class.new
CACHE = {KEY => :foo}
CACHE_BY_ID = {KEY => :foo}.compare_by_identity

def fast
  CACHE_BY_ID[KEY]
end

def slow
  CACHE[KEY]
end

Benchmark.ips do |x|
  x.report('lookup with compare_by_identity') { fast }
  x.report('lookup') { slow }
  x.compare!
end

lookup with compare_by_identity
                         10.781M (± 3.3%) i/s -     54.709M in   5.081038s
              lookup      2.571M (± 3.2%) i/s -     13.089M in   5.097409s

Comparison:
lookup with compare_by_identity: 10781059.3 i/s
              lookup:  2570641.2 i/s - 4.19x  (± 0.00) slower

Same result if lookup is not successful (as long as the hash is not empty...)

I hope we can optimize this a bit.

Dominant language
Ruby
Stars
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Forks
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