I'm trying to publish a posts in my WordPress, but when cointain too much words save but doesn't save the content of description like example. I need take the information inside a file and save it in my DB, but when I press publish or update, the request is send it, but when the page reload, show all the other fields but not the description, when I'm sending around 5 millions of words or even more. How I'm using a script to take the content of a file, my files are around 1mb until 20mb, just text with somes styles. In the DB I'm using longtext as value until I know that support 4Gb, so I don't understand why the posts can save the data.
If you look into LONGTEXT documentation you'll see that:
The effective maximum length of LONGTEXT columns also depends on the configured maximum packet size in the client/server protocol and available memory.
So I would say that 4GB support is only theoretical, in real life your server configuration wouldn't allow operating on such a big chunk of data in one DB field, especially if it's a shared hosting solution.