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From "Deighan, John" <JDeig...@pcgus.com>
Subject RE: ModPerl::RegistryLoader
Date Thu, 21 Jul 2011 12:32:47 GMT
I don't know about ModPerl::RegistryLoader, but the simplest solution is just to "preload"
the interpreters either manually or through a script whenever you restart Apache. In your
httpd.conf file, you control how many interpreters are running and how many hits each interpreter
handles before reloading that interpreter (it can be unlimited if you wish). If, e.g., you're
configured to run 6 interpreters, to be sure they're all loaded, you will need to send 6 concurrent
requests to the server - if you send requests serially, it might use the same interpreter
to serve all 6 requests. In our case, we've set up a web page that is a frames page with multiple
frames, each making the same request to the server. We also have a script that utilizes LWP::UserAgent
to do basically the same thing.

FYI, our application consists of a single script which, depending on the parameters passed
to it, can do many different things. Because of that, once that one script is loaded in an
interpreter, there's nothing else to load. If you have many separate scripts, you can either
do the above, but for each script. However, usually if you have many scripts, each script
is quite small, but may load many Perl libraries (i.e. modules). Keep in mind that if you
load a single script that loads, e.g. 10 Perl libraries, then when another script is required
that uses some of those libraries, Perl will detect the libraries that have already been loaded
and not load them again. For that reason, the other scripts should load very quickly so it
may be sufficient to just preload the script that uses the most of these common libraries.

An httpd.conf configuration we often use is something like:

# Set up the settings for interpreters within mod_perl

PerlInterpStart 12
PerlInterpMax 12
PerlInterpMinSpare 12
PerlInterpMaxSpare 12
PerlInterpMaxRequests 2048

We've found that having a fixed number of interpreters at all times works best for us - we've
had problems in the past where an interpreter is retired by Apache when the load temporarily
drops, only to be started up when the load picks back up (usually within a very short amount
of time), requiring a full reload and slowing down response. That's why the first 4 settings
are all the same. You might want to look it up, but I believe that if PerlInterpMaxRequests
is set to 0, an interpreter will take an unlimited number of hits without reloading. Reloading
an interpreter, however, can help if you have memory leaks or other such "bad" things that
accumulate over time.
________________________________________
From: Jiří Pavlovský [jira@getnet.cz]
Sent: Thursday, July 21, 2011 4:45 AM
To: modperl@perl.apache.org
Subject: ModPerl::RegistryLoader

Hello,

The documentation for "ModPerl::Registry" states: "Note that each httpd
process or "child" must compile each script once, so the first request
to one server may seem slow, but each request there after will be
faster. If your scripts are large and/or make use of many Perl modules,
this difference should be noticeable to the human eye."

I've indeed run into this as my service is not accessed so often so
typically the user requests reaches some httpd child which did not
compile the script yet. So user usually has to wait for the compilation.
In my case the difference is huge (2s versus tenths of ms) which makes
notable difference for the user experience for the various autocomplete
inputs etc.

So I was looking a solution and found ModPerl::RegistryLoader. I'm just
not sure I understand it completely. Is this the "compile once at
startup" solution? Do I just put " my $rlbb =
ModPerl::RegistryLoader->new();" into my startup file?


Thank you,
Jiri

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