Reputation out of sync (upvote not counted)

Question

The reputation displayed in my profile and on https://stackoverflow.com/reputation were the same for quite a while already - the changes to the reputation system worked out well. Still, something went wrong today. First I noticed that the indicator on the "reputation" tab mentioned 15 points reputation increase when I really gained 25 points:

I then checked the total reputation and there is a 10 points mismatch here as well:

I guess that triggering a reputation recalc will fix this - but this still might be a bug worth looking into. Unfortunately, I have no idea what triggered it. From what I can tell, it was an absolutely normal upvote that didn't get counted for some reason.

Edit: I'm pretty certain that my total reputation was 15434 this morning - my network profile however claims that it was 15424. So maybe the issue is with the 10 points I received yesterday, the display in the network profile doesn't show them for some reason.

Answer 1

This happens because of how Linq2SQL works, and it really, really sucks but there's little we can do about it without a major overhaul (getting off Linq2SQL for this, which we have considered, and continue to). So here's how it goes:

Let's assume you're at 100 rep before this happens, to keep it simple.

• OP upvotes your answer, request sent to the server, in progress...
• OP accepts your answer, request sent to server, in progress...
• Upvote request gets your user object (100 reputation)...
• Accept vote request gets your user object (100 reputation)...
• Upvote passes through logic/checks, etc, determines you get 10 points... 110 reputation
• Accept vote passes through similar logic, determines you get 15 points... 115 reputation RUH ROH
• Upvote saves, in the form of Update Users Set Reputation = 110 Where UserId = @Id
• Accept vote saves, in the form of Update Users Set Reputation = 115 Where UserId = @Id
• You now have 115, not 125.

....you see where the problem is here. Since Linq does a = and we can't make Linq2SQL do a Reputation = Reputation + @delta format...last save wins in this kind of race.

The good news is that the reputation history view that tracks every change does not suffer this problem...since it's just inserting 2 rows (in there your summation of rep is what it should be). This allows us to compared, detect and fix up these race results every night, so there's a job to do that until we go nuts and rewrite how rep is saved (it would touch a lot of code).