Removing a key from jsonb is sloooow

[Volkan Unsal <spocksplanet@xxxxxxxxx>]

I'm trying to remove a key from a jsonb column in a table with 10K rows, and the performance is abysmal. When the key is missing, it takes 5 minutes. When the key is present, it takes even longer.

Test with non-existent key:

>> update projects set misc = misc - 'foo';
Time: 324711.960 ms (05:24.712)

What can I do to improve this?