Fleet history is greatly slowing down the save speed of my 100+ year game. For the first time since reinstalling 1.13 from scratch, I opened up the database in an SQL editor and deleted all but the most recent fleet history, which amounted to around 240,000 entries. There were also an inordinate number of GameLog messages about NPR fleets running out of fuel.
Once I deleted all log entries of those two types, saving my game went from 13 seconds before, to just 6 seconds after cleaning the database. (On an SSD, with a top-tier CPU)
I would recommend wiping Fleet History for civilian shipping lines after some number of years (10? 20?) and same with NPRs. Player naval fleet histories should be kept forever.
SJW: Suggestions rather than Bugs. However, I have removed NPR and Shipping Line fleet histories beyond five years.