Sitemaps: Is there such a thing as too big?

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I use the Google XML-Sitemap plugin in all my WordPress installations. It’s a great way to tell Google, Yahoo and Bing when my site updates, and for them to easily see what’s new. It’s a nice set-and-forget kind of plugin.

I’ve been noticing something strange on one of my sites lately – the sitemap keeps timing out and producing nothing but a blank screen. That’s never good – so I’ve been digging into the site to suss out the issue.

I think part of the problem is that this particular site has over 2,700 blog posts. Building the sitemap for that site, and including all the tags and categories was killing the process.

My question today is this – should we be limiting the number of items we put in our sitemap.xml file? Should I cut it off at an arbitrary number, such as 25, or leave all 2,700 in there knowing that only the most recent 5 or so posts are the ones I really want Google to see.