09-13-2011
Lseek implementation
Hi everybody,
i've been googling for ages now and gotten kinda desperate... The question, however, might be rather trivial for the experts: What is it exactly, i.e. physically, the POSIX function (for a file) "lseek" does? Does it trigger some kind of synchronization on disk? Is it just for the file system?
Rationale:
I'm am running some benchmarks to get an idea, how our system (ext4@Debian5) works. I'm having 100 threads reading or writing randomly small requests on disk (POSIX read/write with DIRECT_IO) -> read,lseek,read,lseek,... or write,lseek,write,lseek,... . The mean lseek response time while reading is marginally small, however, the mean lseek response time while writing is appr. as high as the mean response time of a write itself (several ms), and I don't know why...
Any help is appreciated.
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LEARN ABOUT DEBIAN
lwp::protocol::psgi
LWP::Protocol::PSGI(3pm) User Contributed Perl Documentation LWP::Protocol::PSGI(3pm)
NAME
LWP::Protocol::PSGI - Override LWP's HTTP/HTTPS backend with your own PSGI applciation
SYNOPSIS
use LWP::UserAgent;
use LWP::Protocol::PSGI;
# can be Mojolicious, Catalyst ... any PSGI application
my $psgi_app = do {
use Dancer;
setting apphandler => 'PSGI';
get '/search' => sub {
return 'googling ' . params->{q};
};
dance;
};
LWP::Protocol::PSGI->register($psgi_app);
# can hijack any code or module that uses LWP::UserAgent underneath, with no changes
my $ua = LWP::UserAgent->new;
my $res = $ua->get("http://www.google.com/search?q=bar");
print $res->content; # "googling bar"
DESCRIPTION
LWP::Protocol::PSGI is a module to hijack any code that uses LWP::UserAgent underneath such that any HTTP or HTTPS requests can be routed
to your own PSGI application.
Because it works with any code that uses LWP, you can override various WWW::*, Net::* or WebService::* modules such as WWW::Mechanize,
without modifying the calling code or its internals.
use WWW::Mechanize;
use LWP::Protocol::PSGI;
LWP::Protocol::PSGI->register($my_psgi_app);
my $mech = WWW::Mechanize->new;
$mech->get("http://amazon.com/"); # $my_psgi_app runs
METHODS
register
LWP::Protocol::PSGI->register($app);
my $guard = LWP::Protocol::PSGI->register($app);
Registers an override hook to hijack HTTP requests. If called in a non-void context, returns a Guard object that automatically resets
the override when it goes out of context.
{
my $guard = LWP::Protocol::PSGI->register($app);
# hijack the code using LWP with $app
}
# now LWP uses the original HTTP implementations
unregister
LWP::Protocol::PSGI->unregister;
Resets all the overrides for LWP. If you use the guard interface described above, it will be automatically called for you.
AUTHOR
Tatsuhiko Miyagawa <miyagawa@bulknews.net>
COPYRIGHT
Copyright 2011- Tatsuhiko Miyagawa
LICENSE
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
SEE ALSO
Plack::Client LWP::UserAgent
perl v5.12.3 2011-05-12 LWP::Protocol::PSGI(3pm)