Why Computers Can't Count Sometimes

Sometimes, numbers on sites like YouTube and Twitter jump up and down; subscriber counts lag, like-counts bounce all over the place. Why is it so hard for computers to count? To answer that, we need to talk about threading, eventual consistency, and caching.

Thanks to my proofreading team, and to Tomek on camera!

(you can find contact details and social links there too)

[TomScottGo]

This was a really difficult script to write! Folks who know 'eventual consistency' as a more formal term may be annoyed that I'm using it a bit loosely here. Hopefully this works as an explainer for folks who are new to it, though!

[socialblade]

Great video! We get people asking about this topic all the time!

[AbbreviatedReviews]

"Eventual Consistency" is the method I use for getting enough sleep. I'm sure it'll get there one day.

[randomgblsfs]

"Computers are just overgrown calculators"
Something I will say to an AI in the future just to insult it.

[MrZedblade]

I had to explain this to a client once. You did a much better job at it. We had thousands of people per minute interacting with a map and deciding where to place their "donation". There was a counter on the page showing how many "donations" have been made so far and it ran into the millions. We had dozens of AWS Instances, 15 or so RDS Read replicas, and Elasticache servers running to handle the traffic. But the testers (who were sitting next to each other) kept reporting minor discrepancies in their numbers when glancing across at the other tester's screens. I kept trying to explain the concept of "eventual consistency" and that although each individual user should still see the number going up on their screen, two users might just see different figures. But we would still eventually sort it all out and get the down-to-the-penny accurate results at the end of everything. I wish I could have shown them this video.

[SkillsWithPhil]

I've learned so many random things thanks to this channel. These are types of the channels that deserve a YouTube Premium show.

[CheckEmGG]

when the client gives 2 requirements: host 4K videos quickly and have a view counter.
Dev team says: okay we can implement the video stream in a week but the counter will take us 3 months.
This kind of "hard thing is easy and easy thing is hard" happens so much in development.

[hux]

8 minutes, one take, not a single unplanned "um" or "ah": Tom is so damn good at this! How he doesn't have a lucrative TV presenting career is amazing to me. I can only assume he doesn't want one and that he's very happy with what he already has.

[MegaChickenfish]

One of the most surprising things as I learned about IT is how much of this stuff that seems to "just work" really doesn't, but only provides the constant illusion that it does to the front end user. I never thought a calculation like this could be this challenging.

[ryanmorris]

I just want to complement you, Tom, on your narration. I've noticed the One-take approach before on your videos, but this one was impressive. It can't be easy to keep your inflection and pacing interesting for such a long take, let alone doing it in such a conversational tone.

[mcandelaria]

My eyes: see 67 and 68
Me: ah yes, it's all coming together now

[MrLarsjansen]

As a developer, I know about caching and basically everything you talk about, but it is still so interesting and I still learn from it. Especially how to explain things to other people. Thanks!

[LindsayDaly]

*Tom Scott*
*Tom Scott Returns*
*Tom Scott Forever*
*Tom Scott and Robin*

*Tom Scott Begins*
*The Dark Programmer*
*The Dark Programmer Rises*

*Tom Scott vs. VSauce: Dawn of Knowledge*

[AuthenTech]

Anyone remember the old "under 301 club"?! :)

[DzeeBzee]

"Why computers can't count sometimes"




Let's count with Microsoft
1, 2, 3, 95, 98

[megalexantros]

K-pop community needs to see this, so they can stop complaining about views disappearing.

[davr]

I wish everyone saying "lmao 15 likes 0 views youtube is high 😂😂😂" saw this video

[TommyCallaway]

A programmer is going to the grocery store and his wife tells him, "Buy a gallon of milk, and if there are eggs, buy a dozen." So the programmer goes, buys everything, and drives back to his house. Upon arrival, his wife angrily asks him, "Why did you get 12 gallons of milk?" The programmer says, "There were eggs!"

[rexpimplemyer]

Its also a good reason to confirm that the "last one" of an item on ebay, Amazon, etc. is actually "still there" when ordered, or else you may be emailing the refund department as well. For the same reasons just described.

[HYPERPLASMATIER]

right at 7:47, when you said "All out of sync--", my video started to buffer, and I mistook it for comedic effect... It was real. And you sir? You've made me laugh for the sheer fact of how perfect it was to buffer at that moment. Brava, your video makes its own jokes.