On 2/24/2019 1:32 PM, André Warnier (tomcat) wrote:
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.
That's right, thanks for catching it. Should've said child processes
will already have the Perl interpreter loaded.
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
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