Small subset of users get very slow page loads. CPU/bandwidth/etc not under load

This is driving me crazy, so I thought I'd see if anyone could give me a clue. I have a small VPS running Centos 5, newest Apache and MySQL and PHP.

• About 1% of my users report very slow page loads, even for static HTML pages. On the order of 0.1 kbps. But they do eventually get the pages to开发者_JAVA百科 load.

• It is always the same users who are afflicted, and they are always afflicted.

• The server is not under CPU or disk load and it is not memory or disk constrained.

• Throughput is very fast and consistent for all the non-afflicted users.

• Afflicted users can download files very fast from other VPS servers on the same host. So it doesn't seem to be the host.

Has anyone else experienced an issue like this?

/EDIT

• Tracert from affected users is normal

/EDIT2

• Users claim to have tried various operating systems and browsers
• Users come from a range of different geographic regions

It could be some craziness with DNS - esp. if the users are in a corporate environment. Usually, DNS lookups are cached, but if every request also includes a DNS lookup, that might explain the behaviour you identify.

If at all possible, you could ask those users to take their PCs (hopefully laptops) onto another network and try to connect.

You could also ask them to install Firebug (a plugin for the Firefox browser) - this gives you a very visual indication of what's going on.

Does the page include Javascript - esp. analytics tags from other providers? This can sometimes cause a visually slow page - it's downloaded fine, but the browser doesn't render it because it's working on the analytics code.

what does redbot.org say?

Also try running a web page test from a geographical region close to the users having the problem. Look at the waterfall chart and see if there are big wait times or TTFB times.

And in the off chance your users are in a location which may have a CDN/node down or even blocked. For example if your users are in china for example and you have 3rd party widgets being loaded like facebook/twitter they will be blocked by china firewall and will get 10 to 20 second timeouts.