The purpose of this module is to bring your website visitors deeper into your blog. It does that by creating links in your blog post, to other posts in your blog. The idea is once someone has finished reading a post, they will follow the links to other posts in your blog, bringing them "deeper" into your blog.
The module uses a very simplistic algorithm to find other posts in your blog that seem to have something to do with the keyphrase. If you define the keyphrase "magic", the module will try to find a post in your blog that seems to have something to do with magic, and creates a link to that post.
The algorithm used to find relevant posts is very simple... nothing fancy. Assuming the keyphrase defined is "magic", the algorithm works like this:
It searches for blog posts that have the phrase "magic" in either the post title, post excerpt, or post content. It then gives each found post a point value to find out which one is the most relevant to the keyphrase "magic".
A post is given 5 points for each occurrence of the keyphrase in it's title. It's given 3 points for each occurrence of the keyphrase in it's excerpt. It's then given 1 point for each occurrence of the keyphrase in the post's content.
Any post that has 5 or more points is considered a match for the keyphrase. Of all the matching posts, the one with the highest number of points is considered the most relevant to the keyphrase, and it's the URL to that post that will be used in the link the keyphrase.
Since a post is given 5 points for every occurrence of the keyphrase in it's title, and a post needs 5 or more points to be considered a match, having the keyphrase in the title of the post makes it an automatic match. That doesn't mean that'll be the post that is linked to. Other posts still might score higher if the keyphrase is found many times in it's content or excerpt.
The module only has one setting: Don't Search Post Older than Days. If this setting is set to 30, then the module will only look for relevant post that have been modified or created in the past 30 days. The default value if this setting is left blank, is 20 days.
It's important not to set this setting too high. The further back you let the module search, the longer it will take to find the best match for the keyphrase.
You can increase the performance of this module by turning on FULLTEXT indexes in the WordPress database. If FULLTEXT indexes aren't found on the post title, excerpt, or content columns, the module will use a slower method to find relevant posts. If FULLTEXT indexes are on the post title, excerpt, and content columns, then the module will use a much faster MySQL approach to finding relevant posts.
A default install of WordPress does not have FULLTEXT indexes on only columns, but you can add them yourself. Adding the indexes will have no effect on WordPress, and will speed up this module.
You can add the indexes from phpMyAdmin by issuing the following SQL:
ALTER TABLE `wp_posts` ADD FULLTEXT (`post_content`, `post_title`, `post_excerpt`)
Replace 'wp_posts' if you are using something other than the default table prefix. 95% of you will be fine issuing that exact query. Make sure you have the correct database selected when you issue the query.