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Custom performance logging for Rails

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Time Bandits


Time Bandits is a gem plugin for Rails which enhances Rails' controller/view/db benchmark logging.



Without configuration, the standard Rails 'Completed line' will change from its default format

Completed 200 OK in 56ms (Views: 28.5ms, ActiveRecord: 5.1ms)


Completed 200 OK in 56.278ms (Views: 28.488ms, ActiveRecord: 5.111ms(2q,0h))

"ActiveRecord: 5.111ms(2q,0h)" means that 2 SQL queries were executed and there were 0 SQL query cache hits.

However, non-trivial applications also rather often use external services, which consume time that adds to your total response time, and sometimes these external services are not under your control. In these cases, it's very helpful to have an entry in your log file that records the time spent in the exterrnal service (so that you can prove that it wasn't your rails app that slowed down during your slashdotting, for example ;-).

Additional TimeConsumers can be added to the log using the "Timebandits.add" method.


TimeBandits.add TimeBandits::TimeConsumers::Memcached
TimeBandits.add TimeBandits::TimeConsumers::GarbageCollection.instance if GC.respond_to? :enable_stats

Here we've added two additional consumers, which are already provided with the plugin. (Note that GC information requires a patched ruby, see prerequistes below.)

Note: if you run a multithreaded program, the numbers reported for garbage collections and heap usage are partially misleading, because the Ruby interpreter collects stats in global variables shared by all threads.

With these two new time consumers, the log line changes to

Completed 200 OK in 680.378ms (Views: 28.488ms, ActiveRecord: 5.111ms(2q,0h), MC: 5.382(6r,0m), GC: 120.100(1), HP: 0(2000000,546468,18682541,934967))

"MC: 5.382(6r,0m)" means that 6 memcache reads were performed and all keys were found in the cache (0 misses).

"GC: 120.100(1)" tells us that 1 garbage collection was triggered during the request, taking 120.100 milliseconds.

"HP: 0(2000000,546468,18682541,934967)" shows statistics on heap usage. The format is g(s,a,b,l), where

g: heap growth during the request (#slots) s: size of the heap after request processing was completed (#slots) a: number of object allocations during the request (#slots) b: number of bytes allocated by the ruby x_malloc call (#bytes) l: live data set size after last GC (#slots)

Side note for speakers of German: you can use the word "Gesabbel" (eng: drivel) as a mnemonic here ;-)

It's relatively straightforward to write additional time consumers; the more difficult part of this is monkey patching the code which you want to instrument. Have a look at consumers under

and the corresponding patches under


ActiveSupport/Rails >= 5.2 is required. The gem will raise an error if you try to use it with an incompatible version.

You'll need a ruby with the railsexpress GC patches applied, if you want to include GC and heap size information in the completed line. This is very useful, especially if you want to analyze your rails logs using logjam (see

Ruby only contains a subset of the railsexpress patches. To get the full monty, you can use for example rvm and the railsexpress rvm patchsets (see


This plugin started from the code of the 'custom_benchmark' plugin written by tylerkovacs. However, we changed so much of the code that is is practically a full rewrite, hence we changed the name.

Running Tests


docker-compose up
to start Redis, MySQL, RabbitMQ and Memached containers, then run

Release Notes

Version 0.12.2

  • fixed that completed line was logged twice in Rails test environment

Version 0.12.1

  • support having the rails gem in a bundle without activating the time bandits railtie
  • automatically install the garbage collection time bandit in rails applications

Version 0.12.0

  • drops support for Rails versions before 5.2.0 and Ruby versions before 2.2.0
  • makes it possible to use individual time bandits without Rails (e.g. in a Sinatra app)

Version 0.11.0

  • supports rails 6.0.0

Version 0.10.12

  • supports rails 5.0.7

Version 0.10.11

  • support rails 5.2.0

Version 0.10.10

  • fixed regression introduced in 0.10.9

Version 0.10.9

  • added specialized activerecord logging for Rails >= 5.1.5

Version 0.10.8

  • rails has changed render_bind in 5.0.3

Version 0.10.7

  • fixed bug in activerecord monkeypatch for Rails 5.1

Version 0.10.6

  • fixed time calculation for rails 4

Version 0.10.5

  • enabled activerecord monkeypatch for rails 5.1

Version 0.10.4

  • protect against Rails 5 firing on_load handlers multiple times

Version 0.10.3

  • fixed activerecord monkeypatch

Version 0.10.2

  • controller testing fixed for rspec

Version 0.10.1

  • fixed incorrect module prepend which broke controller testing

Version 0.10.0

  • support rails 5

Version 0.9.2

  • sequel gem changes broke sequel time consumer

Version 0.9.1

  • make sure redis times consumer logs keys in ASCII

Version 0.9.0

  • added beetle time consumer

Version 0.8.1

  • bugfix

Version 0.8.0

  • support retrieving current runtime including not yet consumed time

Version 0.7.4

  • use appraisal for testing against multiple rails versions
  • bugfix for actions without render

Version 0.7.3

  • bugfix dalli consumer for rails 4.2

Version 0.7.2

  • support ruby 2.2.0

Version 0.7.1

  • support measuring sequel gem

Version 0.7.0

  • switched to byebug (debugger does not fully support 2.0 and 2.1 not at all)
  • adapted garbage collection statistics to work for 2.1
  • improved rails 4.x compatibility
  • GC time consumer now tries to make the most out of an unpatched ruby

Version 0.6.0

  • added redis time consumer
  • fixed rails 4.0 problems with builtin memcachestore
  • now only consumers which measured something are added to the completed line

Version 0.5.1

  • added license file

Version 0.5

  • has dropped rails 2 support
  • relies on ActiveSupport::Notifications
  • is supposedly thread safe
  • all measurements are thread local (except GC statistics)
  • times are all measured in milliseconds internally
  • added class TimeBandits::TimeConsumers::BaseConsumer to simplify writing custom consumers

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