[LON-CAPA-admin] memory and httpd processes

[Guy Albertelli II]

Hi All,

> I must agree with your assessment: The Linux kernel regards "free" memory
> as wasted memory,

There is the utility 'free' which reports more details:
             total       used       free     shared    buffers        cached
Mem:       2075512    1611560     463952          0     448848        570144
-/+ buffers/cache:     592568    1482944
Swap:      3068404          0    3068404


Where at first glance it looks like 1.6 gigs of memory is 'used'.

But once 'buffers/cache' is removed from the count you see that what
is used is .6 gigs


> > As to why this drastically improves performance, I will let those with much 
> > more knowledge answer that question more intelligently than I can.
> 
> Does it really improve performance or is that more an illusion?

There is a real memesurable difference unfortunately between a
'fresh' apache and an 'old' apache. This has nothing to do with the
amount of memory used or not used, but rather with the speed of
accessing and changing elements in perl's %ENV. Part of the 2.0 devel
cycle has been to reduce the use of hash as much as possible. 

Note

1) people with large numbers (30-40ish is large) of roles are more
affected by this than users with few roles
2) restarting the webserver regularly is a bad idea because this kills
the data caching and can cause a bad situation to get worse


Additionally 2.0 should use significantly less memory in any one
child. (Max apache child size will be aroun 80ish megs rather than the
200ish megs you can see in 1.3) and a centralized memory caching
mechanism should also make webserver restart not hurt, and allow for
more persitant caching while also speeding cache invalidation
(parameter information will update across the whole machine, no more
having to wait 10 minutes to see the effect of the parameter on the
machine you are logged into).


-- 
guy at albertelli.com  LON-CAPA Developer  0-7-2-9-