I've a had one of our servers going down (network wise) but keeping its uptime (so looks the server is not losing its power) recently. I've asked my hosting company to investigate and I've been told, after investigation, that Apache and MySQL were at all time using 80% of the memory and peaking at 95% and that I might be needing to add some more RAM to the server.
One of their justifications to adding more RAM was that I was using the default max connections setting (125 for MySQL and 150 for Apache) and that for handling those 150 simultaneous connections, I would need at least 3Gb of memory instead of the 1Gb I have at the moment.
Now, I understand that tweaking the max connections might be better than me leaving the default setting although I didn't feel it was a concern at the moment, having had servers with the same configuration handle more traffic than the current 1 or 2 visitors before the lunch, telling myself I'd tweak it depending on the visits pattern later.
I've also always known Apache was more memory hungry under default settings than its competitor such as nginx and lighttpd. Nonetheless, looking at the stats of my machine, I'm trying to see how my hosting company got those numbers.
I'm getting:
# free -m
total used free shared buffers cached
Mem: 1000 944 56 0 148 725
-/+ buffers/cache: 71 929
Swap: 1953 0 1953
Which I guess means that yes, the server is reserving around 95% of its memory at the moment but I also thought it meant that only 71 out of the 1000 total were really used by the applications at the moment looking a the buffers/cache row.
Also I don't see any swapping:
# vmstat 60
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 0 57612 151704 742596 0 0 1 1 3 11 0 0 100 0
0 0 0 57604 151704 742596 0 0 0 1 1 24 0 0 100 0
0 0 0 57604 151704 742596 0 0 0 2 1 18 0 0 100 0
0 0 0 57604 151704 742596 0 0 0 0 1 13 0 0 100 0
And finally, while requesting a page:
top - 08:33:19 up 3 days, 13:11, 2 users, load average: 0.06, 0.02, 0.00
Tasks: 81 total, 1 running, 80 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.3%us, 0.3%sy, 0.0%ni, 98.3%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 1024616k total, 976744k used, 47872k free, 151716k buffers
Swap: 2000052k total, 0k used, 2000052k free, 742596k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
24914 www-data 20 0 26296 8640 3724 S 2 0.8 0:00.06 apache2
23785 mysql 20 0 125m 18m 5268 S 1 1.9 0:04.54 mysqld
24491 www-data 20 0 25828 7488 3180 S 1 0.7 0:00.02 apache2
1 root 20 0 2844 1688 544 S 0 0.2 0:01.30 init
...
So, I'd like to know, experts of serverfault:
Do I really need more RAM at the moment?
How do they calculate that for 150 simultaneous connections I'd need 3Gb?
Thanks for your help!
