Slow server, but excellent "top"

[kokoko]

Hi,

I have an Apache server that serves PHP pages.

When the traffic load is important (8-12 PHP pages per second), this server gets very slow to respond to HTTP requests.

But strangely, the server does not seem busy. This is what I get from a "top" command :

top - 23:05:55 up 145 days, 6:56, 1 user, load average: 0.05, 0.06, 0.09
Tasks: 208 total, 1 running, 206 sleeping, 1 stopped, 0 zombie
Cpu(s): 2.0%us, 0.3%sy, 0.0%ni, 97.2%id, 0.0%wa, 0.2%hi, 0.3%si, 0.0%st
Mem: 2047128k total, 1813424k used, 233704k free, 236336k buffers
Swap: 522104k total, 116k used, 521988k free, 844624k cached

I've been looking around to try and solve this issue but can't understand why the server gets slow.
Any idea why the server is so sluggish to respond, while the CPU seems to be "idle"?

The server is slow to serve php scripts, but also static images. ssh does not seem to be slowed down though.

Thanks,
David

[Mr Bo Jangles]

Is it a dedicated server or VPS?

[kokoko]

It is a dedicated server

[vordmeister]

Does the server become slow when the traffic is high, or just at times of day when the traffic tends to be high.

Reminds me of a problem with my last host. My server had no load, but their routers were overloaded (with requests for other servers). I changed host.

Do you see any long delays in a tracert?

[kokoko]

I do not have tracert on the server. But when the server gets slow, I tried to do
- PINGs from this server to public servers (google.com etc)
- PINGs from my computer to this server

all these PINGs were quick and normal. No long delays here.