Rails - Jan 2006 - ActiveRecord: using with multiple threads/DB connections

Hi,

I''m totally new to Ruby and Rails and I''m trying to set up a
prototype
web site. Unfortunately, I''m having problems with ActiveRecord using 
multiple threads.

What I want to do is fairly simple. I have a Controller that receives 
and saves data from the web in the DB, but once that''s done I want to 
process this data in another thread and then save the result in some 
other DB table. I want to do the processing in another thread because it 
may take well over a minute.

When I do this, it works fine as long as I''m not hitting the web server
with additional requests while it is processing. Otherwise, I get all 
sorts of errors either DB-related (StatementInvalid) or in rails itself 
("nil received when it was not expected") or WEBrick dumps a core.

BTW I''m using MySQL with InnoDB tables. I believe it should work fine 
with default settings, but maybe I''m missing something there. I
don''t
think so though.

I read all the ActiveRecord doc I could find and I believe the problem 
is that ActiveRecord globally maps a class to a connection. So there is 
no way to use a separate DB connection to do my asynchronous processing. 
Since all DB statements (across multiple threads) are executed in the 
same connections there is bound to be trouble.

I copy the Controller and some errors I''ve seen below. You can see what
I mean directly in code.

This seems like a very simple case, I''m sure there is something
I''m
doing wrong. What is the ''good'' way to do this? Having a
separate
process to do the backend processing? But then, what about multiple 
threads using ActiveRecord in this backend process?

What am I doing wrong/missing?

I went over the doc many times and couldn''t find anything to solve my 
problem (I checked ActiveRecord::Base.connection and 
.establish_connection, but it doesn''t seem like it will help me in this
case.) I read ActiveRecord is thread safe, but that''s not what
I''m
experiencing. Where does the synchronization take place?

Again, I''m new to RoR so that may be stupid questions. Feel free to
send
me a RTFM, but please provide a link to said manual!  ;)

Thanks,

Max



class ArticlesController < ApplicationController
...
  def create
    @article = Article.new(params[:article])
    if processNewArticle(@article)
      flash[:notice] = ''Article was successfully created.''
      redirect_to :action => ''list''
    else
      render :action => ''new''
    end
  end

  def processNewArticle(article)
    ...do some validation...
    if (!article.save)
      false
    end
    # at this point, we know everything is ok
    # start processing
    Thread.new {
      ... some very long processing ...
    }
    true
  end
...





****************
 ActiveRecord::StatementInvalid in Articles#new

Mysql::Error: Lost connection to MySQL server during query: SHOW FIELDS 
FROM articles

RAILS_ROOT: script/../config/..
Application Trace | Framework Trace | Full Trace

/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/abstract_adapter.rb:88:in
`log''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/mysql_adapter.rb:180:in
`execute''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/mysql_adapter.rb:278:in
`columns''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/base.rb:734:in
`columns''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/base.rb:1663:in
`attributes_from_column_definition''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/base.rb:1185:in
`initialize_without_callbacks''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/callbacks.rb:236:in
`initialize''
./script/../config/../app/controllers/articles_controller.rb:19:in
`new''
./script/../config/../app/controllers/articles_controller.rb:19:in
`new''




********************************
  Mysql::Error in Articles#list

Lost connection to MySQL server during query

RAILS_ROOT: script/../config/..
Application Trace | Framework Trace | Full Trace

/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/vendor/mysql.rb:1093:in
`read''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/vendor/mysql.rb:500:in
`read''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/vendor/mysql.rb:151:in
`real_connect''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/mysql_adapter.rb:316:in
`connect''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/mysql_adapter.rb:164:in
`reconnect!''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/abstract/connection_specification.rb:103:in
`retrieve_connection''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/abstract/connection_specification.rb:20:in
`connection''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/base.rb:518:in
`count_by_sql''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/base.rb:511:in
`count''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.11.2/lib/action_controller/pagination.rb:167:in
`count_collection_for_pagination''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.11.2/lib/action_controller/pagination.rb:188:in
`paginator_and_collection_for''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.11.2/lib/action_controller/pagination.rb:124:in
`paginate''
./script/../config/../app/controllers/articles_controller.rb:11:in 
`list''


-- 
Posted via http://www.ruby-forum.com/.

Digging through the code, I just saw that it is WEBrick that disables 
concurrency...

I now manually set allow_concurrency (to true) in my models. Don''t know
if this is kosher, but it will suffice for now.


-- 
Posted via http://www.ruby-forum.com/.