[#106341] [Ruby master Bug#18369] users.detect(:name, "Dorian") as shorthand for users.detect { |user| user.name == "Dorian" } — dorianmariefr <noreply@...>
Issue #18369 has been reported by dorianmariefr (Dorian Mari辿).
14 messages
2021/11/30
[#106351] [Ruby master Bug#18371] Release branches (release information in general) — "tenderlovemaking (Aaron Patterson)" <noreply@...>
Issue #18371 has been reported by tenderlovemaking (Aaron Patterson).
7 messages
2021/11/30
[ruby-core:105912] [Ruby master Misc#18285] NoMethodError#message uses a lot of CPU/is really expensive to call
From:
"ivoanjo (Ivo Anjo)" <noreply@...>
Date:
2021-11-02 14:32:38 UTC
List:
ruby-core #105912
Issue #18285 has been updated by ivoanjo (Ivo Anjo).
Yeah, I think it's useful to include the object class and possibly its id, but with the default `#inspect` behavior of "print the object and all of its instance variables, and do it recursively", it's a rather sharp edge to have it being called when getting the exception message here.
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Misc #18285: NoMethodError#message uses a lot of CPU/is really expensive to call
https://bugs.ruby-lang.org/issues/18285#change-94455
* Author: ivoanjo (Ivo Anjo)
* Status: Open
* Priority: Normal
----------------------------------------
Hello there! I'm working at Datadog on the ddtrace gem -- https://github.com/DataDog/dd-trace-rb and we ran into this issue on one of our internal testing applications. I also blogged about this issue in <https://ivoanjo.me/blog/2021/11/01/nomethoderror-ruby-cost/>.
### Background
While testing an application that threw a lot of `NoMethodError`s in a Rails controller (this was used for validation), we discovered that service performance was very much impacted when we were logging these exceptions. While investigating with a profiler, the performance impact was caused by calls to `NoMethodError#message`, because this Rails controller had a quite complex `#inspect` method, that was getting called every time we tried to get the `#message` from the exception.
### How to reproduce
```ruby
require 'bundler/inline'
gemfile do
source 'https://rubygems.org'
gem 'benchmark-ips'
end
puts RUBY_DESCRIPTION
class GemInformation
# ...
def get_no_method_error
method_does_not_exist
rescue => e
e
end
def get_runtime_error
raise 'Another Error'
rescue => e
e
end
def inspect # <-- expensive method gets called when calling NoMethodError#message
Gem::Specification._all.inspect
end
end
NO_METHOD_ERROR_INSTANCE = GemInformation.new.get_no_method_error
RUNTIME_ERROR_INSTANCE = GemInformation.new.get_runtime_error
Benchmark.ips do |x|
x.config(:time => 5, :warmup => 2)
x.report("no method error message cost") { NO_METHOD_ERROR_INSTANCE.message }
x.report("runtime error message cost") { RUNTIME_ERROR_INSTANCE.message }
x.compare!
end
```
### Expectation and result
Getting the `#message` from a `NoMethodError` should be no costly than getting it from any other exception.
In reality:
```
ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
no method error message cost
115.390 (賊 1.7%) i/s - 580.000 in 5.027822s
runtime error message cost
6.938M (賊 0.5%) i/s - 35.334M in 5.092617s
Comparison:
runtime error message cost: 6938381.6 i/s
no method error message cost: 115.4 i/s - 60130.02x (賊 0.00) slower
```
### Suggested solutions
1. Do not call `#inspect` on the object on which the method was not found (see <https://github.com/ruby/ruby/blob/e0915ba67964d843832148aeca29a1f8244ca7b1/error.c#L1962>)
2. Cache result of calling `#message` after the first call. Ideally this should be done together with suggestion 1.
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