diff options
Diffstat (limited to 'guides/source/debugging_rails_applications.md')
| -rw-r--r-- | guides/source/debugging_rails_applications.md | 108 |
1 files changed, 71 insertions, 37 deletions
diff --git a/guides/source/debugging_rails_applications.md b/guides/source/debugging_rails_applications.md index a72f54a1b8..226137c89a 100644 --- a/guides/source/debugging_rails_applications.md +++ b/guides/source/debugging_rails_applications.md @@ -1,12 +1,14 @@ Debugging Rails Applications ============================ -This guide introduces techniques for debugging Ruby on Rails applications. By referring to this guide, you will be able to: +This guide introduces techniques for debugging Ruby on Rails applications. -* Understand the purpose of debugging -* Track down problems and issues in your application that your tests aren't identifying -* Learn the different ways of debugging -* Analyze the stack trace +After reading this guide, you will know: + +* The purpose of debugging. +* How to track down problems and issues in your application that your tests aren't identifying. +* The different ways of debugging. +* How to analyze the stack trace. -------------------------------------------------------------------------------- @@ -21,13 +23,13 @@ One common task is to inspect the contents of a variable. In Rails, you can do t ### `debug` -The `debug` helper will return a \<pre>-tag that renders the object using the YAML format. This will generate human-readable data from any object. For example, if you have this code in a view: +The `debug` helper will return a \<pre> tag that renders the object using the YAML format. This will generate human-readable data from any object. For example, if you have this code in a view: ```html+erb <%= debug @post %> <p> <b>Title:</b> - <%=h @post.title %> + <%= @post.title %> </p> ``` @@ -56,7 +58,7 @@ Displaying an instance variable, or any other object or method, in YAML format c <%= simple_format @post.to_yaml %> <p> <b>Title:</b> - <%=h @post.title %> + <%= @post.title %> </p> ``` @@ -86,7 +88,7 @@ Another useful method for displaying object values is `inspect`, especially when <%= [1, 2, 3, 4, 5].inspect %> <p> <b>Title:</b> - <%=h @post.title %> + <%= @post.title %> </p> ``` @@ -105,7 +107,7 @@ It can also be useful to save information to log files at runtime. Rails maintai ### What is the Logger? -Rails makes use of the `ActiveSupport::BufferedLogger` class to write log information. You can also substitute another logger such as `Log4r` if you wish. +Rails makes use of the `ActiveSupport::Logger` class to write log information. You can also substitute another logger such as `Log4r` if you wish. You can specify an alternative logger in your `environment.rb` or any environment file: @@ -164,7 +166,7 @@ class PostsController < ApplicationController logger.debug "The post was saved and now the user is going to be redirected..." redirect_to(@post) else - render :action => "new" + render action: "new" end end @@ -172,7 +174,7 @@ class PostsController < ApplicationController end ``` -Here's an example of the log generated by this method: +Here's an example of the log generated when this controller action is executed: ``` Processing PostsController#create (for 127.0.0.1 at 2008-09-08 11:52:54) [POST] @@ -192,11 +194,13 @@ Redirected to #<Post:0x20af760> Completed in 0.01224 (81 reqs/sec) | DB: 0.00044 (3%) | 302 Found [http://localhost/posts] ``` -Adding extra logging like this makes it easy to search for unexpected or unusual behavior in your logs. If you add extra logging, be sure to make sensible use of log levels, to avoid filling your production logs with useless trivia. +Adding extra logging like this makes it easy to search for unexpected or unusual behavior in your logs. If you add extra logging, be sure to make sensible use of log levels to avoid filling your production logs with useless trivia. ### 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 Active Support 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)) @@ -205,6 +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 --------------------------------- @@ -214,7 +249,7 @@ The debugger can also help you if you want to learn about the Rails source code ### Setup -Rails uses the `debugger` gem to set breakpoints and step through live code. To install it, just run: +You can use the `debugger` gem to set breakpoints and step through live code in Rails. To install it, just run: ```bash $ gem install debugger @@ -233,7 +268,7 @@ class PeopleController < ApplicationController end ``` -If you see the message in the console or logs: +If you see this message in the console or logs: ``` ***** Debugger requested, but was not available: Start server with --debugger to enable ***** @@ -244,12 +279,12 @@ Make sure you have started your web server with the option `--debugger`: ```bash $ rails server --debugger => Booting WEBrick -=> Rails 3.0.0 application starting on http://0.0.0.0:3000 +=> Rails 4.0.0 application starting on http://0.0.0.0:3000 => Debugger enabled ... ``` -TIP: In development mode, you can dynamically `require \'debugger\'` instead of restarting the server, if it was started without `--debugger`. +TIP: In development mode, you can dynamically `require \'debugger\'` instead of restarting the server, even if it was started without `--debugger`. ### The Shell @@ -264,7 +299,7 @@ For example: (rdb:7) ``` -Now it's time to explore and dig into your application. A good place to start is by asking the debugger for help... so type: `help` (You didn't see that coming, right?) +Now it's time to explore and dig into your application. A good place to start is by asking the debugger for help. Type: `help` ``` (rdb:7) help @@ -279,7 +314,7 @@ condition down finish list ps save thread var continue edit frame method putl set tmate where ``` -TIP: To view the help menu for any command use `help <command-name>` in active debug mode. For example: _`help var`_ +TIP: To view the help menu for any command use `help <command-name>` at the debugger prompt. For example: _`help var`_ The next command to learn is one of the most useful: `list`. You can abbreviate any debugging command by supplying just enough letters to distinguish them from other commands, so you can also use `l` for the `list` command. @@ -287,7 +322,7 @@ This command shows you where you are in the code by printing 10 lines centered a ``` (rdb:7) list -[1, 10] in /PathToProject/posts_controller.rb +[1, 10] in /PathTo/project/app/controllers/posts_controller.rb 1 class PostsController < ApplicationController 2 # GET /posts 3 # GET /posts.json @@ -297,7 +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. @@ -323,7 +358,7 @@ On the other hand, to see the previous ten lines you should type `list-` (or `l- ``` (rdb:7) l- -[1, 10] in /PathToProject/posts_controller.rb +[1, 10] in /PathTo/project/app/controllers/posts_controller.rb 1 class PostsController < ApplicationController 2 # GET /posts 3 # GET /posts.json @@ -333,7 +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`. @@ -341,7 +376,7 @@ Finally, to see where you are in the code again you can type `list=` ``` (rdb:7) list= -[1, 10] in /PathToProject/posts_controller.rb +[1, 10] in /PathTo/project/app/controllers/posts_controller.rb 1 class PostsController < ApplicationController 2 # GET /posts 3 # GET /posts.json @@ -351,7 +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 @@ -500,7 +535,7 @@ TIP: You can use the debugger while using `rails console`. Just remember to `req ``` $ rails console -Loading development environment (Rails 3.1.0) +Loading development environment (Rails 4.0.0) >> require "debugger" => [] >> author = Author.first @@ -644,7 +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. @@ -653,21 +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](http://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/) +* [debugger Homepage](https://github.com/cldwalker/debugger) +* [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) |