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Diffstat (limited to 'guides/source/debugging_rails_applications.md')
| -rw-r--r-- | guides/source/debugging_rails_applications.md | 62 |
1 files changed, 47 insertions, 15 deletions
diff --git a/guides/source/debugging_rails_applications.md b/guides/source/debugging_rails_applications.md index 6699098e51..226137c89a 100644 --- a/guides/source/debugging_rails_applications.md +++ b/guides/source/debugging_rails_applications.md @@ -198,7 +198,9 @@ Adding extra logging like this makes it easy to search for unexpected or unusual ### Tagged Logging -When running multi-user, multi-account applications, it’s often useful to be able to filter the logs using some custom rules. `TaggedLogging` in ActiveSupport helps in doing exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications. +When running multi-user, multi-account applications, it's often useful +to be able to filter the logs using some custom rules. `TaggedLogging` +in Active Support helps in doing exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications. ```ruby logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT)) @@ -207,6 +209,37 @@ logger.tagged("BCX", "Jason") { logger.info "Stuff" } # Logs " logger.tagged("BCX") { logger.tagged("Jason") { logger.info "Stuff" } } # Logs "[BCX] [Jason] Stuff" ``` +### Impact of Logs on Performance +Logging will always have a small impact on performance of your rails app, + particularly when logging to disk.However, there are a few subtleties: + +Using the `:debug` level will have a greater performance penalty than `:fatal`, + as a far greater number of strings are being evaluated and written to the + log output (e.g. disk). + +Another potential pitfall is that if you have many calls to `Logger` like this + in your code: + +```ruby +logger.debug "Person attributes hash: #{@person.attributes.inspect}" +``` + +In the above example, There will be a performance impact even if the allowed +output level doesn't include debug. The reason is that Ruby has to evaluate +these strings, which includes instantiating the somewhat heavy `String` object +and interpolating the variables, and which takes time. +Therefore, it's recommended to pass blocks to the logger methods, as these are +only evaluated if the output level is the same or included in the allowed level +(i.e. lazy loading). The same code rewritten would be: + +```ruby +logger.debug {"Person attributes hash: #{@person.attributes.inspect}"} +``` + +The contents of the block, and therefore the string interpolation, is only +evaluated if debug is enabled. This performance savings is only really +noticeable with large amounts of logging, but it's a good practice to employ. + Debugging with the `debugger` gem --------------------------------- @@ -246,7 +279,7 @@ Make sure you have started your web server with the option `--debugger`: ```bash $ rails server --debugger => Booting WEBrick -=> Rails 3.2.13 application starting on http://0.0.0.0:3000 +=> Rails 4.0.0 application starting on http://0.0.0.0:3000 => Debugger enabled ... ``` @@ -299,7 +332,7 @@ This command shows you where you are in the code by printing 10 lines centered a 7 8 respond_to do |format| 9 format.html # index.html.erb - 10 format.json { render :json => @posts } + 10 format.json { render json: @posts } ``` If you repeat the `list` command, this time using just `l`, the next ten lines of the file will be printed out. @@ -335,7 +368,7 @@ On the other hand, to see the previous ten lines you should type `list-` (or `l- 7 8 respond_to do |format| 9 format.html # index.html.erb - 10 format.json { render :json => @posts } + 10 format.json { render json: @posts } ``` This way you can move inside the file, being able to see the code above and over the line you added the `debugger`. @@ -353,7 +386,7 @@ Finally, to see where you are in the code again you can type `list=` 7 8 respond_to do |format| 9 format.html # index.html.erb - 10 format.json { render :json => @posts } + 10 format.json { render json: @posts } ``` ### The Context @@ -502,7 +535,7 @@ TIP: You can use the debugger while using `rails console`. Just remember to `req ``` $ rails console -Loading development environment (Rails 3.2.13) +Loading development environment (Rails 4.0.0) >> require "debugger" => [] >> author = Author.first @@ -646,7 +679,7 @@ In this section, you will learn how to find and fix such leaks by using tool suc [Valgrind](http://valgrind.org/) is a Linux-only application for detecting C-based memory leaks and race conditions. -There are Valgrind tools that can automatically detect many memory management and threading bugs, and profile your programs in detail. For example, a C extension in the interpreter calls `malloc()` but is doesn't properly call `free()`, this memory won't be available until the app terminates. +There are Valgrind tools that can automatically detect many memory management and threading bugs, and profile your programs in detail. For example, if a C extension in the interpreter calls `malloc()` but doesn't properly call `free()`, this memory won't be available until the app terminates. For further information on how to install Valgrind and use with Ruby, refer to [Valgrind and Ruby](http://blog.evanweaver.com/articles/2008/02/05/valgrind-and-ruby/) by Evan Weaver. @@ -655,21 +688,20 @@ Plugins for Debugging There are some Rails plugins to help you to find errors and debug your application. Here is a list of useful plugins for debugging: -* [Footnotes](https://github.com/josevalim/rails-footnotes:) Every Rails page has footnotes that give request information and link back to your source via TextMate. -* [Query Trace](https://github.com/ntalbott/query_trace/tree/master:) Adds query origin tracing to your logs. -* [Query Reviewer](https://github.com/nesquena/query_reviewer:) This rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of warnings for each query that it analyzed. -* [Exception Notifier](https://github.com/smartinez87/exception_notification/tree/master:) Provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application. +* [Footnotes](https://github.com/josevalim/rails-footnotes) Every Rails page has footnotes that give request information and link back to your source via TextMate. +* [Query Trace](https://github.com/ntalbott/query_trace/tree/master) Adds query origin tracing to your logs. +* [Query Reviewer](https://github.com/nesquena/query_reviewer) This rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of warnings for each query that it analyzed. +* [Exception Notifier](https://github.com/smartinez87/exception_notification/tree/master) Provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application. +* [Better Errors](https://github.com/charliesome/better_errors) Replaces the standard Rails error page with a new one containing more contextual information, like source code and variable inspection. +* [RailsPanel](https://github.com/dejan/rails_panel) Chrome extension for Rails development that will end your tailing of development.log. Have all information about your Rails app requests in the browser - in the Developer Tools panel. Provides insight to db/rendering/total times, parameter list, rendered views and more. References ---------- * [ruby-debug Homepage](http://bashdb.sourceforge.net/ruby-debug/home-page.html) * [debugger Homepage](https://github.com/cldwalker/debugger) -* [Article: Debugging a Rails application with ruby-debug](http://www.sitepoint.com/article/debug-rails-app-ruby-debug/) -* [ruby-debug Basics screencast](http://brian.maybeyoureinsane.net/blog/2007/05/07/ruby-debug-basics-screencast/) +* [Article: Debugging a Rails application with ruby-debug](http://www.sitepoint.com/debug-rails-app-ruby-debug/) * [Ryan Bates' debugging ruby (revised) screencast](http://railscasts.com/episodes/54-debugging-ruby-revised) * [Ryan Bates' stack trace screencast](http://railscasts.com/episodes/24-the-stack-trace) * [Ryan Bates' logger screencast](http://railscasts.com/episodes/56-the-logger) * [Debugging with ruby-debug](http://bashdb.sourceforge.net/ruby-debug.html) -* [ruby-debug cheat sheet](http://cheat.errtheblog.com/s/rdebug/) -* [Ruby on Rails Wiki: How to Configure Logging](http://wiki.rubyonrails.org/rails/pages/HowtoConfigureLogging) |