Details here: https://github.com/LemmyNet/lemmy/issues/3165
This will VASTLY decrease the server load of I/O for PostgreSQL, as this mistaken code is doing writes of ~1700 rows (each known Lemmy instance in the database) on every single comment & post creation. This creates record-locking issues given it is writes, which are harsh on the system. Once this is fixed, some site operators will be able to downgrade their hardware! ;)
In this one case, it was hand-written SQL inside a PostgreSQL FUNCTION that the ORM knows nothing about. But there is a approach in the entire application to have live-data from PostgreSQL for every little thing.