We have been using a few useful WordPress plugins on our blogs from the past years and have always been on high server load issues because of which we had to move from shared hosting to dedicated and then move the blogs onto different services like Dedicated, VPS with backups on external drives. The blogs can get heavy spike in the sql queries mainly because of the WordPress plugins which the load goes up and you will have to either upgrade the current VPS or move to a higher configuration. In order to Find Server Load check out our article which is useful for more Cpanel based hosting accounts.
One best suggestion would be to stop using the Contextual Related Posts Plugin which is available at http://wordpress.org/extend/plugins/contextual-related-posts/. No offense to the plugin developer but we have went ahead with multiple tries and have confirmed the below graphs.
The problem with these plugins is that whenever a blog post is read by a visitor, the plugin would run a few SQL Queries and search for other related posts based on title, content and category. This means that on every page load the server gets more resource used and when you disable these kind of plugins, the load is reduced because plugins like these need huge CPU resources.
The above screenshot is taken from our Linode CPU Load Graphs section which shows the current load on the VPS and in order o give you more idea we went ahead by activating the plugin for a few minutes. It’s clearly shown the load moves to the top and because of this the blogs get frequent HTTP Error 503 Service unavailable & Error establishing a database connection errors in the WordPress based blogs.
In order to give another solution in the form of a WordPress plugin which would allow you to display related posts on your blog and feed, we would suggest you to use the YARPP [Yet Another Related Posts Plugin] available at http://wordpress.org/extend/plugins/yet-another-related-posts-plugin/ which is quite better in terms of not just the performance but also takes very less CPU usage giving you less issues on the host. The best part is that this plugin does caching, which would increase the performance and also the speed.
The above screenshot would give you a clear idea on the usage of CPU resources in the form of MySQL Queries when the plugin was activated for a limited period of time.
Alternative Suggestion :
Check out Google Related Links which is a service which wont put any load on your server because it actually finds the related posts based on the Google Indexed Blog posts and pages. Do read our other Tips to Reduce WordPress High Server Usage Problems.
The best part of using the Related Links by Google is that you don’t put any load on your server and the results are loaded super quick.