Uknown meta entries in wp_postmeta

Question

I'm working on a site that has been running for few years and had different maintainers so it's kind of a mess. What I found weird is a lot of entries in wp_postmeta where all the keys are numeric and contain a string like this:

wpAjaxe17fbeda4c811052694cd66e93bf1868f720040882f22c2bba8432e030f010c8069596982baf4cc001345db989c7f98c

where wpAjax is the fixed part and the rest is a sequence of hexadecimal values (or so they seem). These entries are 1170 and the meta_key ranges from 45511 to 46788 and the last post (as in the one with the greatest ID) referred to one of these meta keys is dated almost three years ago, so I think they might have been created by some plugin which has been long forgotten now.

Is there any way to find out if any plugin uses those kind of meta values? I did a search but found nothing.

I'd like to know if they're safe to delete because they seem useless and also mess up the post creation page as they fill the custom field dropdown select (I had to modify the code to exclude numeric meta keys).

Answer 1

The best way to know which plugin was adding them is to search/grep your installation for occurrences of 'wpAjax' and "wpAjax". If you find none (which is likely, since the oldest is 3 years old) safely delete from wp_postmeta where meta_key like 'wpAjax%', or something along those lines, if the latter statement might match something it shouldn't... (Don't forget to flush memcached along the way if you're using it.)

Answer 2

There was a nice function that @MikeSchinkel wrote in an answer to How can I delete orphan keys in Wordpress database tables? about a similar issue in the wp_options table. Its not a direct parallel, but would that approach work for you?

Answer 3

the last post (as in the one with the greatest ID) referred to one of these meta keys is dated almost three years ago

I think it's pretty safe to say they're no longer needed.

Perhaps it was a caching method that got deprecated, or, as you suggested, an old plugin.