Production mode makes many unnecessary SHOW TABLES calls

I believe that should be

   def tables(name = nil) #:nodoc:
     tables = []

•  execute("SHOW TABLES", name).each { |field| tables << field[0] }
  

•  execute("SHOW TABLES", name).each { |field| tables << field[0] } unless @tables
  

•  @tables ||= tables
  

•  tables
  

•  @tables
  

  end

at least that works better for me =0

Sorry I don't really know Ruby, just trying to performance analyze an app. The last statement in the block is the return value right? In the original patch that would be "tables", which is initialized to an empty array. It's only populated if @tables is not yet cached, so after the first run, you'll be returning an empty list instead of the cached one.

Unless I'm missing something about ruby, which I probably am. And my revised patch got de-formated by the comment system =(

ta, Barry

here's a similar method for not calling SHOW FIELDS every time a table is accessed, also seem to help speed.

      def columns(table_name, name = nil)#:nodoc:
        sql = "SHOW FIELDS FROM #{table_name}"
        columns = []
        @columnCache ||= {}
        execute(sql, name).each { |field| columns << MysqlColumn.new(field[0], field[4], field[1], field[2] == "YES") } unless @columnCache[table_name]
        @columnCache[table_name] ||= columns
        @columnCache[table_name]
      end

hth, Barry

Steps to repro:

1. Install will_paginate gem.
   
2. Make some valid code that displays a index of records from some model.
   
3. Include a call to <%= will_paginate %> in the ERB view.
   
4. DO NOT call paginate in the controller.

Result:
You will get an error like:

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each

and there will be many SHOW TABLES calls in the log file (each one taking about 4ms in my case).

I could not edit my post to add more info, so here it is (the stack trace of where the SHOW TABLES is being called from, I believe):

    ...rails303/gems/activesupport-3.0.3/lib/active_support/log_subscriber.rb:93:in `send`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/log_subscriber.rb:93:in `call`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/fanout.rb:47:in `publish`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/fanout.rb:25:in `publish`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/fanout.rb:25:in `each`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/fanout.rb:25:in `publish`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/instrumenter.rb:26:in `instrument`
    ...rails303/gems/activerecord-3.0.3/lib/active_record/connection_adapters/abstract_adapter.rb:195:in `log`
    ...rails303/gems/mysql2-0.2.6/lib/active_record/connection_adapters/mysql2_adapter.rb:314:in `execute`
    ...rails303/gems/mysql2-0.2.6/lib/active_record/connection_adapters/mysql2_adapter.rb:432:in `tables`
    ...rails303/gems/activerecord-3.0.3/lib/active_record/connection_adapters/abstract/schema_statements.rb:21:in `table_exists?`
    ...rails303/gems/activerecord-3.0.3/lib/active_record/base.rb:673:in `table_exists?`
    ...rails303/gems/activerecord-3.0.3/lib/active_record/base.rb:795:in `inspect`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb:16:in `debug_hash`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb:16:in `map`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb:16:in `debug_hash`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb:27:in `__home_base__rvm_gems_ruby_______p____rails____gems_actionpack_______lib_action_dispatch_middleware_templates_rescues__request_and_response_erb__147464093__612719698_0`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/template.rb:135:in `send`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/template.rb:135:in `render`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications.rb:54:in `instrument`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/template.rb:127:in `render`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/render/rendering.rb:59:in `_render_template`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications.rb:52:in `instrument`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/instrumenter.rb:21:in `instrument`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications.rb:52:in `instrument`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/render/rendering.rb:56:in `_render_template`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/render/rendering.rb:26:in `render`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/templates/rescues/template_error.erb:21:in `__home_base__rvm_gems_ruby_______p____rails____gems_actionpack_______lib_action_dispatch_middleware_templates_rescues_template_error_erb__42385148__612684748_0`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/template.rb:135:in `send`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/template.rb:135:in `render`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications.rb:54:in `instrument`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/template.rb:127:in `render`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/render/rendering.rb:59:in `_render_template`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications.rb:52:in `instrument`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications/instrumenter.rb:21:in `instrument`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/notifications.rb:52:in `instrument`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/render/rendering.rb:56:in `_render_template`
    ...rails303/gems/actionpack-3.0.3/lib/action_view/render/rendering.rb:26:in `render`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/show_exceptions.rb:88:in `rescue_action_locally`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/show_exceptions.rb:68:in `render_exception`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/show_exceptions.rb:59:in `call`
    ...rails303/gems/railties-3.0.3/lib/rails/rack/logger.rb:13:in `call`
    ...rails303/gems/rack-1.2.1/lib/rack/runtime.rb:17:in `call`
    ...rails303/gems/activesupport-3.0.3/lib/active_support/cache/strategy/local_cache.rb:72:in `call`
    ...rails303/gems/rack-1.2.1/lib/rack/lock.rb:11:in `call`
    ...rails303/gems/rack-1.2.1/lib/rack/lock.rb:11:in `synchronize`
    ...rails303/gems/rack-1.2.1/lib/rack/lock.rb:11:in `call`
    ...rails303/gems/actionpack-3.0.3/lib/action_dispatch/middleware/static.rb:30:in `call`
    ...rails303/gems/railties-3.0.3/lib/rails/application.rb:168:in `call`
    ...rails303/gems/railties-3.0.3/lib/rails/application.rb:77:in `send`
    ...rails303/gems/railties-3.0.3/lib/rails/application.rb:77:in `method_missing`
    ...rails303/gems/railties-3.0.3/lib/rails/rack/log_tailer.rb:14:in `call`
    ...rails303/gems/rack-1.2.1/lib/rack/content_length.rb:13:in `call`
    ...rails303/gems/rack-1.2.1/lib/rack/handler/webrick.rb:52:in `service`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/httpserver.rb:104:in `service`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/httpserver.rb:65:in `run`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:173:in `start_thread`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:162:in `start`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:162:in `start_thread`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:95:in `start`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:92:in `each`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:92:in `start`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:23:in `start`
    ...ruby-1.8.7-p330/lib/ruby/1.8/webrick/server.rb:82:in `start`
    ...rails303/gems/rack-1.2.1/lib/rack/handler/webrick.rb:13:in `run`
    ...rails303/gems/rack-1.2.1/lib/rack/server.rb:213:in `start`
    ...rails303/gems/railties-3.0.3/lib/rails/commands/server.rb:65:in `start`
    ...rails303/gems/railties-3.0.3/lib/rails/commands.rb:30
    ...rails303/gems/railties-3.0.3/lib/rails/commands.rb:27:in `tap`
    ...rails303/gems/railties-3.0.3/lib/rails/commands.rb:27", "script/rails:6:in `require`", "script/rails:6"

Just a wild guess, but maybe it's something to do with the call to inspect from debug_hash and the inspect is getting called on ActiveRecord::Base (which then calls table_exists?).

Ps.I am using Rails 3.0.3

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