[Mongrel] Requests that make calls from XMLRPC::Client tie up Mongrel

Jonathan Rochkind rochkind at jhu.edu
Wed Nov 18 12:53:22 EST 2009


Do the RpcTask task methods end up using ruby threads to do their 
work?   That call_async  method definitely sounds suspiciously like it 
might.

I've found that ruby threads under mongrel (although I don't think it's 
neccesarily an issue specific to mongrel) sometimes block when you don't 
think they ought to be, or end up in wait state for long periods when it 
doesn't seem like they ought to be.

When I have actual control over my ruby threads, I've found that 
explicitly setting the thread priority of 'background' threads to be 
lower than 0 generally frees things up.   If RpcTask is creating threads 
and you don't want to hack it's code to set thread priorities...  is 
there a synchronous method you can use instead of call_async to make 
your rpc?

Jonathan

Thomas Allen wrote:
> Hi Everyone,
>
> I'm running a Rails site on Mongrel and I can't figure out why a
> particular type of request ties up Mongrel easily. The requests that
> tie up Mongrel call an XML-RPC server like so:
>
> # In the controller
> def site_start
>   if params[:id]
>     @site = Site.find(params[:id])
>     @site.site_start
>     render :json=>{:success=>true}
>   end
> end
>
> # In the model
> def site_start
>   RpcTask.manage(self, 'start')
> end
>
> # In RpcTask
> def manage(site, task)
>   run('manage_task', {
>     :site => site.name,
>     :site_id => site.id,
>     :task => task
>   })
> end
>
> # which calls
> def run(task, task_params = {})
>   begin
>     server = XMLRPC::Client.new2('http://localhost:9192/')
>     result = server.call_async(task,task_params)
>     return result
>   rescue XMLRPC::FaultException => err
>     logger = ActiveRecord::Base.logger
>     logger.error(err.faultCode)
>     logger.error(err.faultString)
>     logger.error(result)
>   end
>   false
> end
>
> If I call the model method directly from the console, the RPC side
> responds very quickly:
>
>   
>>> start = Time.now; Site.first.site_start; (Time.now - start).to_s
>>>       
> => "0.493253"
>
> Removing the body of RpcTask.run results in comparable performance.
> Also, by switching from a single mongrel to a four-mongrel cluster, I
> was able to get the these actions to perform acceptably but I imagine
> that I'm doing something very wrong here to require so much power. Any
> ideas?
>
> Thanks,
> Thomas Allen
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>
>   


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