rails/rails — pull request #15816 by DNNX (2014-06-19 15:57:25+00:00)
Title: Add `logger.debug?` guard to `ActionMailer::LogSubscriber#process`

*TLDR*: The method is 4 times faster when log level is higher than DEBUG.
Also, the other two methods, `#deliver` and `#receive` have similar guard statements,
so this commit adds some symmetry to the code.

This is probably not the most critical part of ActionMailer in terms
of performance, but here are some benchmarks:

```ruby
require 'benchmark/ips'
require 'action_mailer'

event = ActiveSupport::Notifications::Event.new(
'process.action_mailer',
Time.now,
Time.now,
'bf4e2b36ce085fd35b24',
{ mailer: "UserMailer", action: :welcome }
)

ActionMailer::Base.logger = ActiveSupport::Logger.new '/dev/null'

subscriber = ActionMailer::LogSubscriber.new
def subscriber.process_with_guard(event)
return unless logger.debug?
mailer = event.payload[:mailer]
action = event.payload[:action]
debug("\n#{mailer}##{action}: processed outbound mail in #{event.duration.round(1)}ms")
end

Benchmark.ips do |r|
ActionMailer::Base.logger.level = ::Logger::Severity::INFO
r.report('no guard') { subscriber.process(event) }
r.report(' guard') { subscriber.process_with_guard(event) }
end

__END__
Calculating -------------------------------------
no guard 9640 i/100ms
guard 38381 i/100ms
-------------------------------------------------
no guard 169166.9 (±10.2%) i/s - 838680 in 5.007262s
guard 728184.9 (±9.6%) i/s - 3607814 in 4.999218s
```

When log level is DEBUG, the _guarded_ method is a bit slower. This is a
good tradeoff for 4x improvement in production mode, I think.

```ruby
Benchmark.ips do |r|
ActionMailer::Base.logger.level = ::Logger::Severity::DEBUG
r.report('no guard') { subscriber.process(event) }
r.report(' guard') { subscriber.process_with_guard(event) }
end

__END__
Calculating -------------------------------------
no guard 4970 i/100ms
guard 4564 i/100ms
-------------------------------------------------
no guard 55617.4 (±3.5%) i/s - 278320 in 5.010523s
guard 49452.1 (±5.6%) i/s - 251020 in 5.093358s

```