[peruser] Multiplexers and many overloaded vhosts

Janno Sannik janno at kood.ee
Fri Nov 6 00:27:10 MST 2009


On 6.11.2009 6:46, cronfy wrote:
> Hello,
>
> second questuion in a separate message. Do multuiplexers serve other
> requests while waiting for vhosts that reached MaxProcessors limit? I.
> e. we have (a very syntetic example)
>
> * MaxMiltiplexers 5,
> * 10 Vhosts with MaxProcessors 3,
>
> and 5 Vhosts are completely busy (running all 3 processors). Does that
> mean thal all 5 Multiplexers will stuck in waiting for free processor
> for these 5 Vhosts and will not serve requests to other Vhosts?
>
>    
In the past, all the requests would wait in the multiplexers forever. As 
of  0.4.0 beta1, it behaves like this (quoting Taavi Sannik):

  - if the multiplexer cannot pass the request to the processor, then it
will respond to the client with error "503 Service unavailable" (only
works when multiplexer isn't directly passing the socket, eg when SSL is
not enabled and NameVirtualhost is set).

So it just starts to drop requests to this processor pool. There is also 
timing mechanism , which automatically shortens the timeout how long 
multiplexer waits every time it fails to pass on the request to same 
processor pool, if the pool is full. On the server-status page there is 
AVAIL. If that hit's 0 then multiplexer is allready rapidly dropping 
requests to that processor pool in order to protect the system.

I must say that 3 processors is awfully low.
> And how large is the queue for requests that come in at these moments
> (and can not be accepted even by multuiplexers)?
>    
> Thanks in advance.
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>    



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