Re: mod_perl interpreter pool

On 24.02.2019 01:50, Gazzali Jaleel wrote:
>
> On 2/22/2019 2:15 PM, John Dunlap wrote:
>> The Prefork MPM has the following settings:
>> <IfModule mpm_prefork_module>
>>          StartServers                     5
>>          MinSpareServers           5
>>          MaxSpareServers          10
>>          MaxRequestWorkers         150
>>          MaxConnectionsPerChild   0
>> </IfModule>
>>
>> I see these Apache directives but the documentation states that they only apply to a
>> threaded mod_perl/Apache which prefork definitely is not:
>> PerlInterpStart
>> PerlInterpMax
>> PerlInterpMinSpare
>> PerlInterpMaxSpare
>> PerlInterpMaxRequests
>>
>> How does mod_perl allocate interpreters to the prefork worker processes? Is there one
>> perl interpreter for each of preform worker? Is there a pool of perl interpreters which
>> is smaller than the pool of prefork workers? Are there settings for configuring the size
>> of the perl interpreter pool? When a request comes in, does the user have to wait for a
>> perl interpreter process to start or is there already one waiting for them?
>
> If you're asking about mod_perl and prefork:
>
> Apache handles child process creation. Each Apache child process loads the Perl
> interpreter when it starts

Actually, I believe that since this is "prefork", it is the main Apache process (which 
already contains a perl interpreter) which gets "forked" (in other words duplicated, as it 
is) to create a child.  So there is not really a perl interpreter "being started" here (at 
least not in the sense of "being loaded" etc), it is already loaded and it is part of what 
is being duplicated.
(For a more detailed and precise explanation and example, see : 
http://perl.apache.org/docs/2.0/user/handlers/server.html)
Correct me if I'm wrong.

I have no qualms with the rest below, sounds correct to me.

  and the Perl interpreter persists in the process till the
> process terminates. So, at any given time, there're as many Perl interpreters loaded and
> ready as there're Apache processes. When a request comes in, if there's an available
> Apache process to serve the request, it's served. If not, Apache will create a new process
> or queue the request to be served when a process becomes available.
>
> With the numbers above, your server is able to handle 150 simultaneous requests. If
> processes are not busy serving requests, then Apache will kill idle processes based on
> (Min|Max)SpareServers of 5,10. For an overly simple example, if you get 150 requests at
> 8:30 am,  the server could create 145 processes to meet demand. However, if not busy at
> 8:31 am, when everyone has stepped away for coffee, your process count could be down near
> 10. When the boss comes in at 10am and it's back to work, the server will create 140 new
> ... at 10:01am, it's down to 10 again.
>
> Generally, with mod_perl, you don't want Apache to kill idle processes but want them to be
> around, ready to handle new requests. For maximum performance,  (Min|Max)SpareServers
> could be as high as your MaxRequestWorkers. Of course, all of this depends on your RAM,
> CPU utilization etc. and you should be able to find a happy medium as you tweak the numbers.
>
>>
>> --
>> John Dunlap
>> /CTO | Lariat/
>> /
>> /
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