On Tue, Oct 28, 2008 at 10:44:49AM -0400, Francis Dubé wrote: > Jeremy Chadwick a écrit : >> On Mon, Oct 27, 2008 at 12:56:30PM -0700, Chuck Swiger wrote: >> >>> On Oct 27, 2008, at 12:38 PM, FreeBSD wrote: >>> >>>>> You need to keep your MaxClients setting limited to what your >>>>> system can run under high load; generally the amount of system >>>>> memory is the governing factor.  If you set your MaxClients >>>>> higher than that, your system will start swapping under the load >>>>> and once you start hitting VM, it's game over: your throughput >>>>> will plummet and clients will start getting lots of broken >>>>> connections, just as you describe. >>>>> >>>> According to top, we have about 2G of Inactive RAM with 1,5G Active >>>> (4G total RAM with amd64). Swapping is not a problem in this case. >>>> >>> With 4GB of RAM, you're less likely to run into issues, but the most >>> relevant numbers would be the Swap: line in top under high load, or >>> the output of "vmstat 1" / "vmstat -s". >>> > We're monitoring our swap with cacti, and we've never been swapping even > during high load because we dont let apache spawn enough process to do > so.
I'm not sure you fully understand the concept of swapping (the term can be used for a multitude of things). :-) Some processes which sit idle/unused will have portions of their memory "swapped out" (to swap/disk) to allow for actively running processes to utilise physical memory. This is something to keep in mind. >>> It would also be helpful to know what your httpd's are looking like >>> in terms of size, and what your content is like. For Apache serving >>> mostly static content and not including mod_perl, mod_php, etc, you >>> tend to have 5-10MB processes and much of that is shared, so you >>> might well be able to run 400+ httpd children. On the other hand, as >>> soon as you pull in the dynamic language modules like perl or PHP, >>> you end up with much larger process sizes (20 - 40 MB) and much more >>> of their memory usage is per-process rather than shared, so even with >>> 4GB you probably won't be able to run more than 100-150 children >>> before swapping. >>> > Here's an example of top's output regarding our httpd process : > 54326 apache 1 96 0 156M 13108K select 1 0:00 0.15% httpd > 54952 apache 1 96 0 156M 12684K select 1 0:00 0.10% httpd > 52343 apache 1 4 0 155M 12280K select 0 0:01 0.10% httpd > > Most of our page are in HTML with a LOT of images. Few PHP pages, very > light PHP processing. > > 156M x 450 process = way more RAM than what we have (same for RES). > Concretely, how must I interpret these results ? It's as I expected -- you don't understand the difference between SIZE (SZ) and RES (RSS). The simple version: SIZE == amount of memory that's shared across all processes on the machine, e.g. shared libraries. It doesn't mean "156MB is being taken up per process". RES == amount of memory that's specifically allocated to that individual process. The three httpd processes above are taking up a total of ~38MBytes of memory (13108K + 12684K + 12280K). > Right ! I would really appreciate few explanation on this. Do the shared > pages counts as active or inactive RAM ? How can i calculate how much > physical RAM an apache process is taking ? How the VM works in this > regard ? ;) Others will have to explain the shared memory/pages aspect, as it's beyond my understanding. But recent versions of 7.0 and 7.1-PRERELEASE contain a tool called procstat(1) which can help you break down the memory usage within a process. -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB | _______________________________________________ email@example.com mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"