1 Debugging Rails Applications
2 ============================
4 This guide introduces techniques for debugging Ruby on Rails applications. By referring to this guide, you will be able to:
6 * Understand the purpose of debugging
7 * Track down problems and issues in your application that your tests aren't identifying
8 * Learn the different ways of debugging
9 * Analyze the stack trace
11 == View Helpers for Debugging
13 One common task is to inspect the contents of a variable. In Rails, you can do this with three methods:
21 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:
24 ----------------------------------------------------------------------------
30 ----------------------------------------------------------------------------
32 You'll see something like this:
34 ----------------------------------------------------------------------------
37 updated_at: 2008-09-05 22:55:47
38 body: It's a very helpful guide for debugging your Rails app.
39 title: Rails debugging guide
42 created_at: 2008-09-05 22:55:47
46 Title: Rails debugging guide
47 ----------------------------------------------------------------------------
51 Displaying an instance variable, or any other object or method, in yaml format can be achieved this way:
54 ----------------------------------------------------------------------------
55 <%= simple_format @post.to_yaml %>
60 ----------------------------------------------------------------------------
62 The `to_yaml` method converts the method to YAML format leaving it more readable, and then the `simple_format` helper is used to render each line as in the console. This is how `debug` method does its magic.
64 As a result of this, you will have something like this in your view:
66 ----------------------------------------------------------------------------
69 updated_at: 2008-09-05 22:55:47
70 body: It's a very helpful guide for debugging your Rails app.
71 title: Rails debugging guide
74 created_at: 2008-09-05 22:55:47
77 Title: Rails debugging guide
78 ----------------------------------------------------------------------------
82 Another useful method for displaying object values is `inspect`, especially when working with arrays or hashes. This will print the object value as a string. For example:
85 ----------------------------------------------------------------------------
86 <%= [1, 2, 3, 4, 5].inspect %>
91 ----------------------------------------------------------------------------
93 Will be rendered as follows:
95 ----------------------------------------------------------------------------
98 Title: Rails debugging guide
99 ----------------------------------------------------------------------------
101 === Debugging Javascript
103 Rails has built-in support to debug RJS, to active it, set `ActionView::Base.debug_rjs` to _true_, this will specify whether RJS responses should be wrapped in a try/catch block that alert()s the caught exception (and then re-raises it).
105 To enable it, add the following in the `Rails::Initializer do |config|` block inside +environment.rb+:
108 ----------------------------------------------------------------------------
109 config.action_view[:debug_rjs] = true
110 ----------------------------------------------------------------------------
112 Or, at any time, setting `ActionView::Base.debug_rjs` to _true_:
115 ----------------------------------------------------------------------------
116 ActionView::Base.debug_rjs = true
117 ----------------------------------------------------------------------------
120 For more information on debugging javascript refer to link:http://getfirebug.com/[Firebug], the popular debugger for Firefox.
124 It can also be useful to save information to log files at runtime. Rails maintains a separate log file for each runtime environment.
126 === What is The Logger?
128 Rails makes use of Ruby's standard `logger` to write log information. You can also substitute another logger such as `Log4R` if you wish.
130 You can specify an alternative logger in your +environment.rb+ or any environment file:
133 ----------------------------------------------------------------------------
134 ActiveRecord::Base.logger = Logger.new(STDOUT)
135 ActiveRecord::Base.logger = Log4r::Logger.new("Application Log")
136 ----------------------------------------------------------------------------
138 Or in the +Initializer+ section, add _any_ of the following
141 ----------------------------------------------------------------------------
142 config.logger = Logger.new(STDOUT)
143 config.logger = Log4r::Logger.new("Application Log")
144 ----------------------------------------------------------------------------
147 By default, each log is created under `RAILS_ROOT/log/` and the log file name is +environment_name.log+.
151 When something is logged it's printed into the corresponding log if the log level of the message is equal or higher than the configured log level. If you want to know the current log level you can call the `ActiveRecord::Base.logger.level` method.
153 The available log levels are: +:debug+, +:info+, +:warn+, +:error+, and +:fatal+, corresponding to the log level numbers from 0 up to 4 respectively. To change the default log level, use
156 ----------------------------------------------------------------------------
157 config.log_level = Logger::WARN # In any environment initializer, or
158 ActiveRecord::Base.logger.level = 0 # at any time
159 ----------------------------------------------------------------------------
161 This is useful when you want to log under development or staging, but you don't want to flood your production log with unnecessary information.
164 The default Rails log level is +info+ in production mode and +debug+ in development and test mode.
168 To write in the current log use the `logger.(debug|info|warn|error|fatal)` method from within a controller, model or mailer:
171 ----------------------------------------------------------------------------
172 logger.debug "Person attributes hash: #{@person.attributes.inspect}"
173 logger.info "Processing the request..."
174 logger.fatal "Terminating application, raised unrecoverable error!!!"
175 ----------------------------------------------------------------------------
177 Here's an example of a method instrumented with extra logging:
180 ----------------------------------------------------------------------------
181 class PostsController < ApplicationController
185 @post = Post.new(params[:post])
186 logger.debug "New post: #{@post.attributes.inspect}"
187 logger.debug "Post should be valid: #{@post.valid?}"
190 flash[:notice] = 'Post was successfully created.'
191 logger.debug "The post was saved and now is the user is going to be redirected..."
194 render :action => "new"
200 ----------------------------------------------------------------------------
202 Here's an example of the log generated by this method:
204 ----------------------------------------------------------------------------
205 Processing PostsController#create (for 127.0.0.1 at 2008-09-08 11:52:54) [POST]
206 Session ID: BAh7BzoMY3NyZl9pZCIlMDY5MWU1M2I1ZDRjODBlMzkyMWI1OTg2NWQyNzViZjYiCmZsYXNoSUM6J0FjdGl
207 vbkNvbnRyb2xsZXI6OkZsYXNoOjpGbGFzaEhhc2h7AAY6CkB1c2VkewA=--b18cd92fba90eacf8137e5f6b3b06c4d724596a4
208 Parameters: {"commit"=>"Create", "post"=>{"title"=>"Debugging Rails",
209 "body"=>"I'm learning how to print in logs!!!", "published"=>"0"},
210 "authenticity_token"=>"2059c1286e93402e389127b1153204e0d1e275dd", "action"=>"create", "controller"=>"posts"}
211 New post: {"updated_at"=>nil, "title"=>"Debugging Rails", "body"=>"I'm learning how to print in logs!!!",
212 "published"=>false, "created_at"=>nil}
213 Post should be valid: true
214 Post Create (0.000443) INSERT INTO "posts" ("updated_at", "title", "body", "published",
215 "created_at") VALUES('2008-09-08 14:52:54', 'Debugging Rails',
216 'I''m learning how to print in logs!!!', 'f', '2008-09-08 14:52:54')
217 The post was saved and now is the user is going to be redirected...
218 Redirected to #<Post:0x20af760>
219 Completed in 0.01224 (81 reqs/sec) | DB: 0.00044 (3%) | 302 Found [http://localhost/posts]
220 ----------------------------------------------------------------------------
222 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.
224 == Debugging with ruby-debug
226 When your code is behaving in unexpected ways, you can try printing to logs or the console to diagnose the problem. Unfortunately, there are times when this sort of error tracking is not effective in finding the root cause of a problem. When you actually need to journey into your running source code, the debugger is your best companion.
228 The debugger can also help you if you want to learn about the Rails source code but don't know where to start. Just debug any request to your application and use this guide to learn how to move from the code you have written deeper into Rails code.
232 The debugger used by Rails, +ruby-debug+, comes as a gem. To install it, just run:
235 ----------------------------------------------------------------------------
236 $ sudo gem install ruby-debug
237 ----------------------------------------------------------------------------
239 In case you want to download a particular version or get the source code, refer to the link:http://rubyforge.org/projects/ruby-debug/[project's page on rubyforge].
241 Rails has had built-in support for ruby-debug since Rails 2.0. Inside any Rails application you can invoke the debugger by calling the `debugger` method.
246 ----------------------------------------------------------------------------
247 class PeopleController < ApplicationController
253 ----------------------------------------------------------------------------
255 If you see the message in the console or logs:
257 ----------------------------------------------------------------------------
258 ***** Debugger requested, but was not available: Start server with --debugger to enable *****
259 ----------------------------------------------------------------------------
261 Make sure you have started your web server with the option +--debugger+:
264 ----------------------------------------------------------------------------
265 ~/PathTo/rails_project$ script/server --debugger
266 => Booting Mongrel (use 'script/server webrick' to force WEBrick)
267 => Rails 2.2.0 application starting on http://0.0.0.0:3000
270 ----------------------------------------------------------------------------
273 In development mode, you can dynamically `require \'ruby-debug\'` instead of restarting the server, if it was started without `--debugger`.
275 In order to use Rails debugging you'll need to be running either *WEBrick* or *Mongrel*. For the moment, no alternative servers are supported.
279 As soon as your application calls the `debugger` method, the debugger will be started in a debugger shell inside the terminal window where you launched your application server, and you will be placed at ruby-debug's prompt `(rdb:n)`. The _n_ is the thread number. The prompt will also show you the next line of code that is waiting to run.
281 If you got there by a browser request, the browser tab containing the request will be hung until the debugger has finished and the trace has finished processing the entire request.
285 ----------------------------------------------------------------------------
286 @posts = Post.find(:all)
288 ----------------------------------------------------------------------------
290 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?)
292 ----------------------------------------------------------------------------
294 ruby-debug help v0.10.2
295 Type 'help <command-name>' for help on a specific command
298 backtrace delete enable help next quit show trace
299 break disable eval info p reload source undisplay
300 catch display exit irb pp restart step up
301 condition down finish list ps save thread var
302 continue edit frame method putl set tmate where
303 ----------------------------------------------------------------------------
306 To view the help menu for any command use `help <command-name>` in active debug mode. For example: _+help var+_
308 The next command to learn is one of the most useful: `list`. You can also abbreviate ruby-debug commands by supplying just enough letters to distinguish them from other commands, so you can also use +l+ for the +list+ command.
310 This command shows you where you are in the code by printing 10 lines centered around the current line; the current line in this particular case is line 6 and is marked by +=>+.
312 ----------------------------------------------------------------------------
314 [1, 10] in /PathToProject/posts_controller.rb
315 1 class PostsController < ApplicationController
320 => 6 @posts = Post.find(:all)
322 8 respond_to do |format|
323 9 format.html # index.html.erb
324 10 format.xml { render :xml => @posts }
325 ----------------------------------------------------------------------------
327 If you repeat the +list+ command, this time using just `l`, the next ten lines of the file will be printed out.
329 ----------------------------------------------------------------------------
331 [11, 20] in /PathTo/project/app/controllers/posts_controller.rb
336 15 # GET /posts/1.xml
338 17 @post = Post.find(params[:id])
340 19 respond_to do |format|
341 20 format.html # show.html.erb
342 ----------------------------------------------------------------------------
344 And so on until the end of the current file. When the end of file is reached, the +list+ command will start again from the beginning of the file and continue again up to the end, treating the file as a circular buffer.
348 When you start debugging your application, you will be placed in different contexts as you go through the different parts of the stack.
350 ruby-debug creates a content when a stopping point or an event is reached. The context has information about the suspended program which enables a debugger to inspect the frame stack, evaluate variables from the perspective of the debugged program, and contains information about the place where the debugged program is stopped.
352 At any time you can call the `backtrace` command (or its alias `where`) to print the backtrace of the application. This can be very helpful to know how you got where you are. If you ever wondered about how you got somewhere in your code, then `backtrace` will supply the answer.
354 ----------------------------------------------------------------------------
356 #0 PostsController.index
357 at line /PathTo/project/app/controllers/posts_controller.rb:6
359 at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175
360 #2 ActionController::Base.perform_action_without_filters
361 at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175
362 #3 ActionController::Filters::InstanceMethods.call_filters(chain#ActionController::Fil...,...)
363 at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/filters.rb:617
365 ----------------------------------------------------------------------------
367 You move anywhere you want in this trace (thus changing the context) by using the `frame _n_` command, where _n_ is the specified frame number.
369 ----------------------------------------------------------------------------
371 #2 ActionController::Base.perform_action_without_filters
372 at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175
373 ----------------------------------------------------------------------------
375 The available variables are the same as if you were running the code line by line. After all, that's what debugging is.
377 Moving up and down the stack frame: You can use `up [n]` (`u` for abbreviated) and `down [n]` commands in order to change the context _n_ frames up or down the stack respectively. _n_ defaults to one. Up in this case is towards higher-numbered stack frames, and down is towards lower-numbered stack frames.
381 The debugger can list, stop, resume and switch between running threads by using the command `thread` (or the abbreviated `th`). This command has a handful of options:
383 * `thread` shows the current thread.
384 * `thread list` is used to list all threads and their statuses. The plus + character and the number indicates the current thread of execution.
385 * `thread stop _n_` stop thread _n_.
386 * `thread resume _n_` resumes thread _n_.
387 * `thread switch _n_` switches the current thread context to _n_.
389 This command is very helpful, among other occasions, when you are debugging concurrent threads and need to verify that there are no race conditions in your code.
391 === Inspecting Variables
393 Any expression can be evaluated in the current context. To evaluate an expression, just type it!
395 This example shows how you can print the instance_variables defined within the current context:
397 ----------------------------------------------------------------------------
398 @posts = Post.find(:all)
399 (rdb:11) instance_variables
400 ["@_response", "@action_name", "@url", "@_session", "@_cookies", "@performed_render", "@_flash", "@template", "@_params", "@before_filter_chain_aborted", "@request_origin", "@_headers", "@performed_redirect", "@_request"]
401 ----------------------------------------------------------------------------
403 As you may have figured out, all of the variables that you can access from a controller are displayed. This list is dynamically updated as you execute code. For example, run the next line using `next` (you'll learn more about this command later in this guide).
405 ----------------------------------------------------------------------------
407 Processing PostsController#index (for 127.0.0.1 at 2008-09-04 19:51:34) [GET]
408 Session ID: BAh7BiIKZmxhc2hJQzonQWN0aW9uQ29udHJvbGxlcjo6Rmxhc2g6OkZsYXNoSGFzaHsABjoKQHVzZWR7AA==--b16e91b992453a8cc201694d660147bba8b0fd0e
409 Parameters: {"action"=>"index", "controller"=>"posts"}
410 /PathToProject/posts_controller.rb:8
411 respond_to do |format|
412 -------------------------------------------------------------------------------
414 And then ask again for the instance_variables:
416 ----------------------------------------------------------------------------
417 (rdb:11) instance_variables.include? "@posts"
419 ----------------------------------------------------------------------------
421 Now +@posts+ is a included in the instance variables, because the line defining it was executed.
424 You can also step into *irb* mode with the command `irb` (of course!). This way an irb session will be started within the context you invoked it. But be warned: this is an experimental feature.
426 The `var` method is the most convenient way to show variables and their values:
428 ----------------------------------------------------------------------------
430 (rdb:1) v[ar] const <object> show constants of object
431 (rdb:1) v[ar] g[lobal] show global variables
432 (rdb:1) v[ar] i[nstance] <object> show instance variables of object
433 (rdb:1) v[ar] l[ocal] show local variables
434 ----------------------------------------------------------------------------
436 This is a great way to inspect the values of the current context variables. For example:
438 ----------------------------------------------------------------------------
440 __dbg_verbose_save => false
441 ----------------------------------------------------------------------------
443 You can also inspect for an object method this way:
445 ----------------------------------------------------------------------------
446 (rdb:9) var instance Post.new
447 @attributes = {"updated_at"=>nil, "body"=>nil, "title"=>nil, "published"=>nil, "created_at"...
448 @attributes_cache = {}
450 ----------------------------------------------------------------------------
453 The commands `p` (print) and `pp` (pretty print) can be used to evaluate Ruby expressions and display the value of variables to the console.
455 You can use also `display` to start watching variables. This is a good way of tracking the values of a variable while the execution goes on.
457 ----------------------------------------------------------------------------
458 (rdb:1) display @recent_comments
459 1: @recent_comments =
460 ----------------------------------------------------------------------------
462 The variables inside the displaying list will be printed with their values after you move in the stack. To stop displaying a variable use `undisplay _n_` where _n_ is the variable number (1 in the last example).
466 Now you should know where you are in the running trace and be able to print the available variables. But lets continue and move on with the application execution.
468 Use `step` (abbreviated `s`) to continue running your program until the next logical stopping point and return control to ruby-debug.
471 You can also use `step+ _n_` and `step- _n_` to move forward or backward _n_ steps respectively.
473 You may also use `next` which is similar to step, but function or method calls that appear within the line of code are executed without stopping. As with step, you may use plus sign to move _n_ steps.
475 The difference between `next` and `step` is that `step` stops at the next line of code executed, doing just a single step, while `next` moves to the next line without descending inside methods.
477 For example, consider this block of code with an included +debugger+ statement:
480 ----------------------------------------------------------------------------
481 class Author < ActiveRecord::Base
485 def find_recent_comments(limit = 10)
487 @recent_comments ||= comments.find(
489 :conditions => ["created_at > ?", 1.week.ago],
494 ----------------------------------------------------------------------------
497 You can use ruby-debug while using script/console. Just remember to `require "ruby-debug"` before calling the `debugger` method.
499 ----------------------------------------------------------------------------
500 /PathTo/project $ script/console
501 Loading development environment (Rails 2.1.0)
502 >> require "ruby-debug"
504 >> author = Author.first
505 => #<Author id: 1, first_name: "Bob", last_name: "Smith", created_at: "2008-07-31 12:46:10", updated_at: "2008-07-31 12:46:10">
506 >> author.find_recent_comments
507 /PathTo/project/app/models/author.rb:11
509 ----------------------------------------------------------------------------
511 With the code stopped, take a look around:
513 ----------------------------------------------------------------------------
515 [6, 15] in /PathTo/project/app/models/author.rb
517 7 @recent_comments ||= comments.find(
519 9 :conditions => ["created_at > ?", 1.week.ago],
524 ----------------------------------------------------------------------------
526 You are at the end of the line, but... was this line executed? You can inspect the instance variables.
528 ----------------------------------------------------------------------------
530 @attributes = {"updated_at"=>"2008-07-31 12:46:10", "id"=>"1", "first_name"=>"Bob", "las...
531 @attributes_cache = {}
532 ----------------------------------------------------------------------------
534 +@recent_comments+ hasn't been defined yet, so it's clear that this line hasn't been executed yet. Use the +next+ command to move on in the code:
536 ----------------------------------------------------------------------------
538 /PathTo/project/app/models/author.rb:12
541 @attributes = {"updated_at"=>"2008-07-31 12:46:10", "id"=>"1", "first_name"=>"Bob", "las...
542 @attributes_cache = {}
544 @recent_comments = []
545 ----------------------------------------------------------------------------
547 Now you can see that the +@comments+ relationship was loaded and @recent_comments defined because the line was executed.
549 If you want to go deeper into the stack trace you can move single `steps`, through your calling methods and into Rails code. This is one of the best ways to find bugs in your code, or perhaps in Ruby or Rails.
553 A breakpoint makes your application stop whenever a certain point in the program is reached. The debugger shell is invoked in that line.
555 You can add breakpoints dynamically with the command `break` (or just `b`). There are 3 possible ways of adding breakpoints manually:
557 * `break line`: set breakpoint in the _line_ in the current source file.
558 * `break file:line [if expression]`: set breakpoint in the _line_ number inside the _file_. If an _expression_ is given it must evaluated to _true_ to fire up the debugger.
559 * `break class(.|\#)method [if expression]`: set breakpoint in _method_ (. and \# for class and instance method respectively) defined in _class_. The _expression_ works the same way as with file:line.
561 ----------------------------------------------------------------------------
563 Breakpoint 1 file /PathTo/project/vendor/rails/actionpack/lib/action_controller/filters.rb, line 10
564 ----------------------------------------------------------------------------
566 Use `info breakpoints _n_` or `info break _n_` to list breakpoints. If you supply a number, it lists that breakpoint. Otherwise it lists all breakpoints.
568 ----------------------------------------------------------------------------
569 (rdb:5) info breakpoints
572 ----------------------------------------------------------------------------
574 To delete breakpoints: use the command `delete _n_` to remove the breakpoint number _n_. If no number is specified, it deletes all breakpoints that are currently active..
576 ----------------------------------------------------------------------------
578 (rdb:5) info breakpoints
580 ----------------------------------------------------------------------------
582 You can also enable or disable breakpoints:
584 * `enable breakpoints`: allow a list _breakpoints_ or all of them if no list is specified, to stop your program. This is the default state when you create a breakpoint.
585 * `disable breakpoints`: the _breakpoints_ will have no effect on your program.
587 === Catching Exceptions
589 The command `catch exception-name` (or just `cat exception-name`) can be used to intercept an exception of type _exception-name_ when there would otherwise be is no handler for it.
591 To list all active catchpoints use `catch`.
593 === Resuming Execution
595 There are two ways to resume execution of an application that is stopped in the debugger:
597 * `continue` [line-specification] (or `c`): resume program execution, at the address where your script last stopped; any breakpoints set at that address are bypassed. The optional argument line-specification allows you to specify a line number to set a one-time breakpoint which is deleted when that breakpoint is reached.
598 * `finish` [frame-number] (or `fin`): execute until the selected stack frame returns. If no frame number is given, the application will run until the currently selected frame returns. The currently selected frame starts out the most-recent frame or 0 if no frame positioning (e.g up, down or frame) has been performed. If a frame number is given it will run until the specified frame returns.
602 Two commands allow you to open code from the debugger into an editor:
604 * `edit [file:line]`: edit _file_ using the editor specified by the EDITOR environment variable. A specific _line_ can also be given.
605 * `tmate _n_` (abbreviated `tm`): open the current file in TextMate. It uses n-th frame if _n_ is specified.
609 To exit the debugger, use the `quit` command (abbreviated `q`), or its alias `exit`.
611 A simple quit tries to terminate all threads in effect. Therefore your server will be stopped and you will have to start it again.
615 There are some settings that can be configured in ruby-debug to make it easier to debug your code. Here are a few of the available options:
617 * `set reload`: Reload source code when changed.
618 * `set autolist`: Execute `list` command on every breakpoint.
619 * `set listsize _n_`: Set number of source lines to list by default to _n_.
620 * `set forcestep`: Make sure the `next` and `step` commands always move to a new line
622 You can see the full list by using `help set`. Use `help set _subcommand_` to learn about a particular +set+ command.
625 You can include any number of these configuration lines inside a `.rdebugrc` file in your HOME directory. ruby-debug will read this file every time it is loaded. and configure itself accordingly.
627 Here's a good start for an `.rdebugrc`:
629 ----------------------------------------------------------------------------
633 ----------------------------------------------------------------------------
635 == Debugging Memory Leaks
637 A Ruby application (on Rails or not), can leak memory - either in the Ruby code or at the C code level.
639 In this section, you will learn how to find and fix such leaks by using Bleak House and Valgrind debugging tools.
643 link:http://github.com/fauna/bleak_house/tree/master[BleakHouse] is a library for finding memory leaks.
645 If a Ruby object does not go out of scope, the Ruby Garbage Collector won't sweep it since it is referenced somewhere. Leaks like this can grow slowly and your application will consume more and more memory, gradually affecting the overall system performance. This tool will help you find leaks on the Ruby heap.
649 ----------------------------------------------------------------------------
650 sudo gem install bleak_house
651 ----------------------------------------------------------------------------
653 Then setup you application for profiling. Then add the following at the bottom of config/environment.rb:
656 ----------------------------------------------------------------------------
657 require 'bleak_house' if ENV['BLEAK_HOUSE']
658 ----------------------------------------------------------------------------
660 Start a server instance with BleakHouse integration:
662 ----------------------------------------------------------------------------
663 RAILS_ENV=production BLEAK_HOUSE=1 ruby-bleak-house ./script/server
664 ----------------------------------------------------------------------------
666 Make sure to run a couple hundred requests to get better data samples, then press `CTRL-C`. The server will stop and Bleak House will produce a dumpfile in `/tmp`:
668 ----------------------------------------------------------------------------
669 ** BleakHouse: working...
670 ** BleakHouse: complete
671 ** Bleakhouse: run 'bleak /tmp/bleak.5979.0.dump' to analyze.
672 ----------------------------------------------------------------------------
674 To analyze it, just run the listed command. The top 20 leakiest lines will be listed:
676 ----------------------------------------------------------------------------
678 Final heap size 191691 filled, 220961 free
679 Displaying top 20 most common line/class pairs
680 89513 __null__:__null__:__node__
681 41438 __null__:__null__:String
682 2348 /opt/local//lib/ruby/site_ruby/1.8/rubygems/specification.rb:557:Array
683 1508 /opt/local//lib/ruby/gems/1.8/specifications/gettext-1.90.0.gemspec:14:String
684 1021 /opt/local//lib/ruby/gems/1.8/specifications/heel-0.2.0.gemspec:14:String
685 951 /opt/local//lib/ruby/site_ruby/1.8/rubygems/version.rb:111:String
686 935 /opt/local//lib/ruby/site_ruby/1.8/rubygems/specification.rb:557:String
687 834 /opt/local//lib/ruby/site_ruby/1.8/rubygems/version.rb:146:Array
689 ----------------------------------------------------------------------------
691 This way you can find where your application is leaking memory and fix it.
693 If link:http://github.com/fauna/bleak_house/tree/master[BleakHouse] doesn't report any heap growth but you still have memory growth, you might have a broken C extension, or real leak in the interpreter. In that case, try using Valgrind to investigate further.
697 link:http://valgrind.org/[Valgrind] is a Linux-only application for detecting C-based memory leaks and race conditions.
699 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.
701 For further information on how to install Valgrind and use with Ruby, refer to link:http://blog.evanweaver.com/articles/2008/02/05/valgrind-and-ruby/[Valgrind and Ruby] by Evan Weaver.
703 == Plugins for Debugging
705 There are some Rails plugins to help you to find errors and debug your application. Here is a list of useful plugins for debugging:
707 * link:http://github.com/drnic/rails-footnotes/tree/master[Footnotes]: Every Rails page has footnotes that give request information and link back to your source via TextMate.
708 * link:http://github.com/ntalbott/query_trace/tree/master[Query Trace]: Adds query origin tracing to your logs.
709 * link:http://github.com/dan-manges/query_stats/tree/master[Query Stats]: A Rails plugin to track database queries.
710 * link:http://code.google.com/p/query-reviewer/[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.
711 * link:http://github.com/rails/exception_notification/tree/master[Exception Notifier]: Provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application.
712 * link:http://github.com/defunkt/exception_logger/tree/master[Exception Logger]: Logs your Rails exceptions in the database and provides a funky web interface to manage them.
716 * link:http://www.datanoise.com/ruby-debug[ruby-debug Homepage]
717 * link:http://www.sitepoint.com/article/debug-rails-app-ruby-debug/[Article: Debugging a Rails application with ruby-debug]
718 * link:http://brian.maybeyoureinsane.net/blog/2007/05/07/ruby-debug-basics-screencast/[ruby-debug Basics screencast]
719 * link:http://railscasts.com/episodes/54-debugging-with-ruby-debug[Ryan Bate's ruby-debug screencast]
720 * link:http://railscasts.com/episodes/24-the-stack-trace[Ryan Bate's stack trace screencast]
721 * link:http://railscasts.com/episodes/56-the-logger[Ryan Bate's logger screencast]
722 * link:http://bashdb.sourceforge.net/ruby-debug.html[Debugging with ruby-debug]
723 * link:http://cheat.errtheblog.com/s/rdebug/[ruby-debug cheat sheet]
724 * link:http://wiki.rubyonrails.org/rails/pages/HowtoConfigureLogging[Ruby on Rails Wiki: How to Configure Logging]
725 * link:http://blog.evanweaver.com/files/doc/fauna/bleak_house/files/README.html[Bleak House Documentation]
729 http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/5[Lighthouse ticket]
731 * November 3, 2008: Accepted for publication. Added RJS, memory leaks and plugins chapters by link:../authors.html#miloops[Emilio Tagua]
732 * October 19, 2008: Copy editing pass by link:../authors.html#mgunderloy[Mike Gunderloy]
733 * September 16, 2008: initial version by link:../authors.html#miloops[Emilio Tagua]