For some reason the rerender of HTML for the page https://commons.wikimedia.org/wiki/User_talk:BKMzastavka got caught in an infinite loop creating millions of copies of the same thing in the stashing table.
This resulted in 100 writes per second into the stashing table and a partition that grown to 150 gb.
It seems like the loop is originate within RESTBase itself. One weird thing about the page is than in the latest table there was a revision which according to MW doesn't even exist:
select * from "commons_T_parsoid__ng_html".data where "_domain" = 'commons.wikimedia.org' and key = 'User_talk:BKMzastavka'; User_talk:BKMzastavka | 269290610 | ed7e5e6e-d283-11e7-830e-948a9d85eed2 User_talk:BKMzastavka | 269070421 | b00719f8-d1cf-11e7-9ac5-c1fd1670d9dd User_talk:BKMzastavka | 269070421 | e1aca272-d188-11e7-86f8-ead141b8ee5a
The revision number 269290610 doesn't exist. So, on an attempt to save a new render of 269070421, the latest bucket reported 412 (meaning that the content should be stored in the fallback bucket). The check for content equality probably also failed because of that 269290610 revision existence. The most pressing open question is why did it begin infinitely looping?