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Feature #16557

Deduplicate Regexp literals

Added by byroot (Jean Boussier) 6 months ago. Updated 4 months ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:96979]

Description

Pull Request: https://github.com/ruby/ruby/pull/2859

Context

Real world application contain many duplicated Regexp literals.

From a rails/console in Redmine:

>> ObjectSpace.each_object(Regexp).count
=> 6828
>> ObjectSpace.each_object(Regexp).uniq.count
=> 4162
>> ObjectSpace.each_object(Regexp).to_a.map { |r| ObjectSpace.memsize_of(r) }.sum
=> 4611957 # 4.4 MB total
>> ObjectSpace.each_object(Regexp).to_a.map { |r| ObjectSpace.memsize_of(r) }.sum - ObjectSpace.each_object(Regexp).to_a.uniq.map { |r| ObjectSpace.memsize_of(r) }.sum
=> 1490601 # 1.42 MB could be saved

Here's the to 10 most duplicated regexps in Redmine:

147: /"/
107: /\s+/
103: //
89: /\n/
83: /'/
76: /\s+/m
37: /\d+/
35: /\[/
33: /./
33: /\\./

Any empty Rails application will have a similar amount of regexps.

The feature

Since https://bugs.ruby-lang.org/issues/16377 made literal regexps frozen, it is possible to deduplicate literal regexps without changing any semantic and save a decent amount of resident memory.

The patch

I tried implementing this feature in a way very similar to the frozen_strings table, it's functional but I'm having trouble with a segfault on Linux: https://github.com/ruby/ruby/pull/2859

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