Re: Advice on Apache

[Mark T. <ma...@fr...>]

> Obviously there is an advantage to mod_perl's persistence, speeding 
> up response processing significatively (I've seen claims of 
> improvements in the order of 10 to 100 times!, depending on code) in 
> exchange for a bit more RAM. This is clearly a usable benefit!
> 
> Where do you all think mod_perl can fit into sql-ledger's scheme of things?

It probably doesn't need to for the vast majority of SQL-Ledger users:

We do virtual-hosting and have offered mod_perl on our servers for several years now. Our own e-commerce stuff 
and anything else that will generate large numbers of hits is built in Perl/mod_perl. mod_perl is probably one of the 
single most powerful technologies available to web developers using Perl.

mod_perl integrates the Perl language interpreter into the Apache web server. This has two main advantages:

1. the developer gets access to the Apache API via Perl, allowing Apache modules (or handlers) to be written in Perl
2. Perl scripts can run as Apache::Registry scripts, meaning they are parsed, compiled and executed in the         
Apache process itself.

Once a script has been parsed and compiled into the Apache parent process (preferably at Apache start-up) the 
next request that calls the script is answered from the compiled version cached by Apache. This means the 
overhead of starting a Perl process, parsing and compiling the script for each request is avoided. The result is 
performance that comes close to that of compiled C-code in many cases.

So, mod_perl is used for speed and power by folks that use Perl. But, for applications like SQL-Ledger its benefits 
are likely to be minimal at best (unless the same system is being used by many users simultaneously).

There are a couple of caveats when using mod_perl. But they do help enforce good coding practices. Because the 
Perl scripts/handlers/Apache-modules are persistent name-spaces and variable-scoping become critical. A global 
variable will be shared by all Apache processes that handle requests for a particular script. mod_perl Apache 
processes can be pretty large. On modern systems this is usually not a problem. On a busy server it is generally 
preferable to have an Apache child process using 10MB-RAM (a lot is shared memory on OS's like Linux) than to 
fork and exec a new Perl process for every hit to a frequently requested resource.

There is no harm in using a mod_perl capable server to run SQL-Ledger since Perl scripts can always be run as 
standard CGI processes. The Apache configuration can control the use of mod_perl on a per-file/script basis.

For more info see:
http://perl.apache.org/guide/

Mark

Mark Tiramani
FREDO Internet Services
ma...@fr...