FreeBSD 6.2-STABLE && apache 2.2.4 = bad performance. Help!

[Chuck Swiger]

On Jul 18, 2007, at 4:15 PM, Michael Vaughn wrote:
>> Your Apache processes are huge; mine typically stay under 20MB in
>> VSIZE even with PHP loaded (this is Apache-2.0.59 + PHP 4.4.7 or PHP
>> 5.2.x).  I suspect your PHP app(s) are leaking memory or otherwise
>> have some significant problems with the way they are coded.
>
> The SIZE is huge; What they really use is about 20-30Mb as would be  
> expected.

I tend to see 20MB VSIZE and 15-18 MB RES; 140MB VSIZE and 20MB RES  
means 120MB is either swapped out, allocated but never referenced, or  
in "inactive" memory state.

That memory profile of your apache is surprising and resembles only a  
few cases I ran into, where people were writing huge Perl+DBD/DBI  
scripts via mod_perl that inflated RAM usage significantly and caused  
similar problems until some sanity checking and limiting of result  
sets was implemented in their code.

>> > I had to lower MaxClients on apache substancially from 128 to 32,
>> > or loads would quickly go to 40+. (Other servers with dual cpus  
>> instead of
>> > quad and apache 1.3 on freebsd 6.0 don't have this problem)
>>
>> The fact that your server starts dogging out around 40 processes is
>> not surprising-- 40 * ~140MB per httpd child = 5600 MB, which exceeds
>> the available physical memory in the system, at which point you start
>> swapping excessively and the performance is going to plummet.
>
> Swap: 8000M Total, 8000M Free

OK-- was this under your 30+ simultaneous clients load where you  
start seeing problems, or was this at a point where the system was  
closer to idle?

>> > Am I the only one getting terrible performance with apache2 on
>> > FreeBSD 6 ?
>>
>> Apache-2.0 + PHP does just fine for me; I'm not sure that Apache-2.2
>> + PHP5 has been as well tested or is as lightweight in resources as
>> the older Apache 1.3 or 2.0 flavors are.  It might be worth
>> downgrading to an older Apache to test things out, but it really does
>> sound like the web app you've got is the problem more than FreeBSD 6
>> or the rest of your infrastructure....
>
> I might give 2.0 a go; I felt this was worth mentioning because  
> most of the cpu time is spent on system, even with just 32 MaxClients.
>
>  Do note I mentioned the same app runs on inferior, with loads of  
> 0-4 (not optimal, but there is no noticeable slowdown there) on  
> FreeBSD 6.0/i386 apache 1.3 (this is 6.2-STABLE/amd64 apache  
> 2.2.4), and that is also part of the reason I went ahead and mailed  
> the list. It doesn't make sense that a server with twice the ram,  
> twice the processors and a recent OS version is spending 70% of the  
> time in system% whereas the old servers running for 400+ days spend  
> about 25% in system%.

True enough.  There's a fair difference in memory profile between the  
32-bit x86 flavor of FreeBSD and the AMD64 flavor, although I  
wouldn't expect it to result in such an extreme difference.  It'd be  
interesting to see how the 32-bit version of 6.2 does and whether it  
makes a noticable change, if you get a chance to switch out for  
testing...

-- 
-Chuck