This is a privacy-related update that I've always intended to implement on Tildes, and I finally spent some time on it this week.
Keeping eternal records of everything that every user ever voted on is some of the most sensitive data that sites with a voting system have. Your voting history says a huge amount about you, your interests and opinions, and can even serve as a decent proxy for showing what times you were active on the site, what posts you were reading, and how long you spent reading the comments on each of them. In exchange for these major privacy implications, you get the tiny benefit of being able to tell which old posts you voted on (if you even go back to old posts).
So now, to match up with Tildes's general approach of deleting as much sensitive data as possible after 30 days, the voting on posts closes when they're 30 days old. After a post's voting is closed, the records of which individual users voted on that post are deleted, but the count of how many votes there were is kept. So old posts will continue showing their same "scores" exactly the same as before, but there will be no record of which individual users cast those votes.
However, this isn't a purely positive update: the main downside is that the voting does need to be closed (otherwise there would be no way to prevent people from voting again after their first vote is deleted), which prevents the occasionally useful ability to vote on old topics or comments. Overall though, voting on older posts is extremely rare, with less than 1% of the votes on Tildes ever made on something that was over 30 days old at the time of voting.
When the "delete old sensitive data" job runs for the first time after this update later today, 97% of the voting data in the database will be deleted. That's a massive decrease in the amount of sensitive data the site is retaining, and something that most sites would never consider doing, because of the value of that data for behavior analysis and ad-targeting.