Rails - Sep 2006 - rails threads / contexts / fastcgi - can someone explain ???

Hi,

Would someone be able to explain how ruby class/object contexts work 
from the point of view of a deployed rails application using FASTCGI and 
noting there are multiple Ruby processes running (say on dreamhost for 
example).  Some questions to help clarify what I''m trying to
understand:

a) how do incoming URL requests get spread across the multiple Ruby 
processes (let''s say there are 5 processes)?

b) What component organising/manages this?  (e.g. plugin in apache?)

c) is there any ''stickness'' that occurs? i.e. where a request
from
person A that goes to ruby process 2 the first time will go to process 2 
again for the next person A request (I assume no?)


d) is there any sharing of contexts between the ruby processes?  i.e. 
Can a ruby class variable be "seen" across processes?

e) is there any equivalent to the java static class variable (which can 
be accessed from any user request coming in which is being hosted within 
the same web-container on the same JVM)?   I understand there isn''t an 
equivalent in ruby?


f) does the running ruby process handle multiple simultaneous user 
requests at the same time?  i.e. is it operating in a multi-threaded 
mode?

g) If so (for last question) is there any scope for collisions when 
using class variables (@@variable), or is each user request (i.e. each 
HTTP request) totally isolated from every other request at the 
ruby/rails application level?  (of course the database would be shared). 
i.e. could both users/requests share the same class variable somehow??


h) what non-database caching raw ruby techniques are there for same 
caching a bunch of constants stored in a properties type file - perhaps 
put the properties/configuration setting in a ruby file itself as 
constants.  Is it effectively already "cached" once it is
"require"ed
via ruby then holding it in memory?  or does ruby re-load that file each 
time?

i) what would be simplest / rudimentory way to load/cache a bunch of 
properties/configuration parameters for an application?  (would it be as 
per my suggestion in item h)


Signed
Still a bit confused about ruby/rails contexts  :)

Thanks in advance





















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

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

On 9/12/06, Greg Hauptmann
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> Hi,
I''m not a FastCGI expert, but I''ll try to answer your
questions as best I can.
> Would someone be able to explain how ruby class/object contexts work
> from the point of view of a deployed rails application using FASTCGI and
> noting there are multiple Ruby processes running (say on dreamhost for
> example).  Some questions to help clarify what I''m trying to
understand:
>
> a) how do incoming URL requests get spread across the multiple Ruby
> processes (let''s say there are 5 processes)?
By whatever''s in front of the processes. If you''re using
lighttpd/fastcgi, for example, lighttpd will do the balancing across
the multiple rails fastcgi listeners.
> b) What component organising/manages this?  (e.g. plugin in apache?)
>
> c) is there any ''stickness'' that occurs? i.e. where a
request from
> person A that goes to ruby process 2 the first time will go to process 2
> again for the next person A request (I assume no?)
That''s going to depend on the particular implementation. I
haven''t
seen it implemented anywhere, but that doesn''t mean that someone
hasn''t done so.
> d) is there any sharing of contexts between the ruby processes?  i.e.
> Can a ruby class variable be "seen" across processes?
By default, no. You can use an in-memory cache accessible by all
listeners (on the same box).
> e) is there any equivalent to the java static class variable (which can
> be accessed from any user request coming in which is being hosted within
> the same web-container on the same JVM)?   I understand there
isn''t an
> equivalent in ruby?
I''m not sure what you''re asking here. There are class
variables in ruby.
> f) does the running ruby process handle multiple simultaneous user
> requests at the same time?  i.e. is it operating in a multi-threaded
> mode?
It doesn''t.
> g) If so (for last question) is there any scope for collisions when
> using class variables (@@variable), or is each user request (i.e. each
> HTTP request) totally isolated from every other request at the
> ruby/rails application level?  (of course the database would be shared).
> i.e. could both users/requests share the same class variable somehow??
Again, I''m not sure what you''re asking. Rails runs
single-threaded.
> h) what non-database caching raw ruby techniques are there for same
> caching a bunch of constants stored in a properties type file - perhaps
> put the properties/configuration setting in a ruby file itself as
> constants.  Is it effectively already "cached" once it is
"require"ed
> via ruby then holding it in memory?  or does ruby re-load that file each
> time?
Put config stuff in the environment files. In production mode those
don''t get reloaded.

-ryan

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

On Sep 12, 2006, at 3:30 AM, Greg Hauptmann wrote:
>
> Hi,
>
> Would someone be able to explain how ruby class/object contexts work
> from the point of view of a deployed rails application using  
> FASTCGI and
> noting there are multiple Ruby processes running (say on dreamhost for
> example).  Some questions to help clarify what I''m trying to  
> understand:
>
> a) how do incoming URL requests get spread across the multiple Ruby
> processes (let''s say there are 5 processes)?
The front end webserver balances between the fcgi listeners. On  
dreamhost this would be apache doing that I believe.
>
> b) What component organising/manages this?  (e.g. plugin in apache?)
>
see above
> c) is there any ''stickness'' that occurs? i.e. where a
request from
> person A that goes to ruby process 2 the first time will go to  
> process 2
> again for the next person A request (I assume no?)
Not with apache and usually not with fcgi. some front end proxies  
allow this like pound or nginx. Its called sticky session adn it  
makes sure a clients request always goes to the same backend.

With rails I don''t think this is a good idea. You need to code your  
rails apps so that any backend can answer a request.

>
>
> d) is there any sharing of contexts between the ruby processes?  i.e.
> Can a ruby class variable be "seen" across processes?
No the ruby processes are totally independent. you can share state  
through the database or via a drb server or memcached.
>
> e) is there any equivalent to the java static class variable (which  
> can
> be accessed from any user request coming in which is being hosted  
> within
> the same web-container on the same JVM)?   I understand there
isn''t an
> equivalent in ruby?
I''m not familiar with Java enough to know what this means exactly.  
But I don''t think rails has what you want here. Can you explain what  
you want to do with this and then I can help?
>
>
> f) does the running ruby process handle multiple simultaneous user
> requests at the same time?  i.e. is it operating in a multi-threaded
> mode?
No each request to rails gets gaurded with  mutex. So each of your  
rails processes will only serve one request at a time and new  
requests will queue up waiting their turn. So you need to watch out  
if your users are dong huge file uploads. If you have three fcgi''s  
and people try to upload 5 huge files at the same time, two of them  
will queue up and wait until one of the other uploads is done.
>
> g) If so (for last question) is there any scope for collisions when
> using class variables (@@variable), or is each user request (i.e. each
> HTTP request) totally isolated from every other request at the
> ruby/rails application level?  (of course the database would be  
> shared).
> i.e. could both users/requests share the same class variable somehow??
On each request, your models and controllers are instantiated and go  
from there. @@classvars can get confusing because they are visible  
throughout the entire inheritance tree from where they are defined.  
So you can use these but think it thru carefully if you do as it can  
get confusing and if you don''t do it right it can cause leakages  
between sessions.
>
>
> h) what non-database caching raw ruby techniques are there for same
> caching a bunch of constants stored in a properties type file -  
> perhaps
> put the properties/configuration setting in a ruby file itself as
> constants.  Is it effectively already "cached" once it is
"require"ed
> via ruby then holding it in memory?  or does ruby re-load that file  
> each
> time?
If you put a constant in environment.rb it will only load on bootup  
and will stay in memory until the procees is killed.

>
> i) what would be simplest / rudimentory way to load/cache a bunch of
> properties/configuration parameters for an application?  (would it  
> be as
> per my suggestion in item h)
I would make a yaml config file and then load the contents of that  
into a constant in environment.rb. That works great for certain  
things. Of course you don''t want to store a huge amount of data thins  
way but for config options it works great.

>
>
> Signed
> Still a bit confused about ruby/rails contexts  :)
No worries, its a bit difficult to figure out on your own. But once  
you follow a few guidelines it will become clear.
> Thanks in advance
>
You''re welcome!

Cheers-
-Ezra


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Thanks heaps Ezra & Ryan for answering.  I''ll respond below:

e) Equivalent to Java Static Class
- I didn''t explain that well my question, but it was really what does
the
language offer itself in terms of shared in-memory data across any/all
requests.
- Ryan points out there is really no equivalent
- RYAN: When you mentioned in-memory cache options I guess you were
referring to some external operating system support?  What did you have in
mind for a unix installation?

f) running ruby process handle multiple simultaneous requests
- EZRA: Tks.  Do you whether a typical apache/fastcgi setup will detect the
"I don''t have enough running ruby processes" and start new
ones?  In
particular I''m using dreamhost at the moment for hosting &
wondering whether
I need to configure anything here myself, or request it from the hosting
provider.

g) scope for collisions when using class variables (@@variable)
- Ezra: I''d love to understand what you meant by "think it thru
carefully if
you do as it can get confusing and if you don''t do it right it can
cause
leakages between sessions" (i.e. re use of class variables) - are you able
to expand?

i) way to load/cache a bunch of properties/configuration parameters
- Tks
- I was considering usage for simple localisation, and have a couple of
different files each with say 5 to 10 pages of key,value pairs.  How do this
sound re size?  The only other way would be to hit the database each time in
fact no?  i.e. is there any in-between approach that ruby/rails offers (e.g.
lazy-loading type support that is then cached?)

Thanks again
Greg


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---