In my Google Webmaster Tools account, there are warnings about my site.
Some URLs listed in this sitemap have a high response time. This may indicate a problem with your server or with the content of the page.
What is the solution?
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It merely means that when the crawler visited some of your pages, the response speed was slow. It may or may not be an intermittent issue but I would recommend that you do a performance audit of your pages.
If you're not sure where/how to proceed, Google page insights is a good bet: https://developers.google.com/speed/pagespeed/insights/
Google is telling you that some pages found in your sitemap loaded very slowly. There are online testing tools to check the speed of your site. There are several, but the first good looking service is http://gtmetrix.com/. But while this is an option people like, read on.
Google does tell you what pages loaded slowly using Google Analytics, Site Speed, Page Timmings - select Average Page Load Time in the first column. If it is not sorted by descending times, then click the column header to change the sort. If you have not signed up for Google Analytics, I suggest you do. It is a gold mine of information.
First, you need to identify what where the issue is. I would run some tests on that page using one of the following tools:
These two will give you an idea of why your page is slow to respond. It could be the map taking too long to call home or it could be something related to your hosting environment. Usually if its your hosting then the entire site would be very slow.
Second, analyze the reports and identify the issue. Below are some things to look out for:
1) Bad TTFB (Time To First Byte) - 9 out of 10 times this means that you need to switch hosting
2) Any pages that are over 1 MB in size. You should avoid having any of your pages blow up like that. Common causes for this are big images that have not been optimized for web or a lot of extra code (usually happens with CMS)
3) A very high number of connection requests. For a small static site I would say that anything over 30 requests is too much for a single page. For a CMS site I would say anything under 60 - 80 is a norm.
4) If you use social media buttons on your site then look out for connection requests that take a very long time. Sometimes Twitter takes forever to load over https.
In conclusion. You can identify 99% of these issues using the tools provided above and they are pretty simple to fix once you know what they are.