When I first signed up at Linode my sites all loaded very fast. Now after about 6 weeks they are very slow to respond. I have 3 main sites, 2 of which have forums attached. It appears the forums load pretty fast but the wordpress sites are taking upto 10 seconds to load on my connection.Initailly these sites loaded up in a couple of seconds or less.

It appears that the delay is between clicking the page in favorites and the actual domain name displaying in the url bar. Once the url is in place in the url bar the site loads fast.

where do I start in working out

A) if there is a problem
B) Correcting the problem.

This appears to be the slowest site :

http://www.real-whitby.co.uk/

Do you have any Wordpress caching modules installed? I've heard there are some really good plugins that cache a ton of the data from the database so that queries don't have to be run every time.

Hi There, In have w3total cache installed. However its always been installed. The sites ran exceptionally fast for about 3 - 4 weeks now they slowed right down.

Hi, I just tried to access your site, but it looks like things are completely down right now: http://www.downforeveryoneorjustme.com/www.real-whitby.co.uk

Is there anything new going on with resource utilization on your server? To rule out external factors, are things like ping times and transmission speed still the same?

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Amateur, eager to learn.
My hematology, oncology, and chemotherapy regimen wiki

Looks like it's not a speed issue with loading resources (which any plugin for caching/compressing will not help), but instead the clients are waiting 3+ second just to get a response to the request.

This sounds like either:
1. Apache/Nginx is handing on requests
2. PHP is running very slowly holding up the request

To rule out 2, if you copy all of the source of the HTML (go to View Source on the homepage, copy all the code, and create a file in your Document Root called test.html (or simular). Go to the webpage but with /test.html instead, and see how quick the page runs, if it's instant, then its probably PHP, if its still slow then it seems to be your Web Server. Can you then post you Web Server Configuration.

Regards,
Matt