On Thu, 2003-09-25 at 05:36, Ruslan U. Zakirov wrote: > I'm looking for suggestions, information, may be atricles about > different memory usage issues concerned with mod_perl1.
The best information about this kind of tuning is at http://perl.apache.org/ and in the book "Practical mod_perl" from O'Reilly. > On one Russian forum man posted an review of memory "leaks"(caveats): > > sub handler > { > my $r = shift; > $r->send_http_header('text/plain'); > print "Hello, World!\n"; > print ttt(); > return OK; > } > sub ttt > { > my $huge_text = 'x' x 1000000; > my $huge_text = $huge_text . "abc" . "bcd"; > return 1; > } > > 1) Restart Apache > 2) Start `top` > 3) Request. > 4) Apache eats ~4MB instead of 1.... When I run this (with a few changes to make it a valid module), my apache uses 3784K of memory total, and more than half of that is shared, leaving only 1620K per child actually being used. It doesn't grow if I keep hitting the same handler over and over. There is no leak. > I know that mod_perl(or may be perl) don't free memory of $huge_string > because most likely it will be needed in next call, but also it take > another MBs for concatenation. Why? It's just a matter of how Perl does the concatenation. When you write it this way, it creates a temporary string and uses more memory. It doesn't take the additional memory if you do it like this instead: $huge_text .= "abc" . "bcd"; You can see the same effect in a command-line Perl program. > But if I want to prevent huge memory usage I can add undef($huge_text); > just before return, but undef force freeing of only 1MB. ~3MB leaks and > make me use MaxRequestsPerChild... :( It's not really leaking (it doesn't grow). You can't undef the temporary string you created because you have no name to reference it by. > It's an hypothetical example, but now we use huge system(RT from Best > Practical) and without limiting requests per child we fall in apache > lock down. I don't know enough about RT to comment on it, but it's a mistake to run any mod_perl system without Apache::SizeLimit (or Apache::GTopLimit) enabled. - Perrin
