Now that we require MySQL 4.1.2, we can look into using UUIDs in WordPress.
Universally unique identifiers are numbers that are unique in time and space. In the database world, they’re primarily used in order to work with data that is created in a decentralized manner. It allows to characterize a piece of data that isn’t stored in the database yet, to merge data from separate databases without needing to work around ID conflicts, etc.
The lack of genuine UUIDs introduces all sorts of quirks in the WP editor when we’re dealing with yet to be saved posts. #9471, #10456, #11145, #11990, and many more underscore the architectural problem that we’re facing. The media-related tickets exacerbate the issue.
Mark recently opened #11889 and suggested that we a) always create a new post when hitting the new post button, and b) have a garbage collector clean things up periodically. It is a solution, but I feel that using UUIDs — which were designed to deal with this kind of stuff — would be simpler.
Using them would mean pre-assigning a UUID to new posts, and placing it in a hidden field. Since this UUID characterizes our yet to be saved post, we can safely pass it around to an autosave handler, a media thickbox, etc., allowing to create the post on the fly when necessary.
Further down the stream, we introduce a slight change in our insert/update post handler: when saving a post whose ID is not assigned yet, we start by verifying if that post exists already — by querying the posts table’s post_guid field to know if that UUID exists.