Post change history update occasional delay?

I've noticed that sometimes the post change history updates especially slower, with a delay of several hours. For example, the history of post #5480528 currently states that the last edit was by me 8 hours ago adding a few tags including black shirt, however, if you look at the actual post, there're tags such as dress shirt added later on that are not found on the history page.

I've checked logged off to make sure that I am not the only one getting this. There also weren't any delay on other history counts such as wiki history or artist commentary history when the post change delay happens. I was assuming there're some kind of site updates/maintenance operating that caused these delays and moved on, but recently they've been annoying me a bit more as I need to constantly check the post change history to stay up-to-date when I'm tagging. So I want to know what exactly is this, just to make sure?

The post versions database lives in Amazon's SQS, which means that every time a post's tags get edited, our servers have to update the post versions database in the remote machine. When a big BUR such as the ones in topic #21283 gets approved, a large amount of edits is generated in a very small amount of time, and they all have to be synced to the remote database, so this causes delays while the post versions database tries to catch up.

If you look at the post versions page, right under the search options there's a warning that says "Recent updates may not have been processed yet. The most recently processed version was about X time ago." Usually the time displayed there is a few seconds ago, but because of those large BURs the history processing can slow down a lot. Right now it's at 3 hours ago.

There's nothing you can do other than wait until it's caught up.

Thanks for the info, it's nice to know why at least, ensures myself that I didn't crush anything.