why app updates can sometimes break features that have worked well for a long time
In: Technology
Because apps are complicated and have a lot of connected pieces. There are dozens of people working on them and they all don’t know everything. So one guy makes a change that effects something another guy did 3 years ago and now something doesn’t work
To change a wall mounted light fixture, you have to turn off the circuit breaker. You forget to switch it back on and ship the new version of the room to all your clients. The new fixture looks great, but none of the lights work, because the breaker is off.
That, but with computer code.
Because software can be really complicated under the hood.
But also because sometimes two related features are both developed on their own, and while New-Feature1 works with Old-Feature2, and New-Feature2 works with Old-Feature1, for some reason New-Feature1 and New-Feature2 might not work well together, and the combined result wasn’t tested thoroughly compared to each individual change.
Software is complicated, even for seemingly simple things. Let’s just take something like an upvote on Reddit. You might think that you just write something to give an upvote when someone hits the button, right?
But no, it’s much more complicated. Software will be encapsulated so that each discrete part is done by discrete code, but this also makes it reusable for other things. What does that mean?
Reddit supports both mobile and web based, and they don’t want to write everything twice, so for the webpage and their mobile apps, they would just make a button that can receive a click for the upvote.
This will then call an API to say “X user submitted an upvote on Y post/comment”
This will need to get written to a database, but lots of things you do on Reddit needs to get written to a database, so there will be a separate part that writes to the database.
You don’t want everyone who is accessing Reddit to have to hit that database when they are scrolling, because that would mean millions of database calls as you scroll Reddit just to see all of the upvote and comment counts. So instead, all of this data will be kept in an in-memory cache.
That write to the database will then also need to update that in-memory cache. This will probably be done in another piece of code.
Then the success of this DB write and cache update needs to get sent to the original upvote API.
This will then send something to either the web page or the mobile app to notify it to update the upvote count on their view.
Now, let’s say that someone at Reddit is working on an update to the award system. They make some changes, but it also will affect that database write and the cache update, adding an extra field to all of those. They didn’t realize the upvote API used some of those same modules in its call. This change works perfectly for the award update.
Then there is also how software is tested. Reddit can’t have a group of people testing every possible thing Reddit can do on iPhone, Android and the web with each and every update. Instead most testing is done via code itself. But this means that each step in that above chain is tested separately. And often some of those tests are poorly written, so perhaps the upvote API will only check that the database got updated, but not the cache when a write it done. So even running all of the tests, that passes.
However when the update goes out, now the upvote button API doesn’t work as this change makes it so the upvote API gets an error on the cache update, which reports an error to the API which reports an error to you the user. However it is still kind of working, your upvote did go in, it just didn’t update the cache so your view didn’t get updated. But if there was something else that triggers a cache refresh, then it would refresh from the DB, get the correct value and things then work.
You’ve built a Lego set (an app), it’s a tower with 10 identical floors. You decide one day, “I want to add a balcony near the bottom!”
So you unstack the floors. You build the balcony (feature). You connect it to the floor you want near the bottom, it fits perfectly. You put the whole tower back together and its gorgeous. You’re done.
Then one day your friend comes over (user) and, after hearing about your tower, decides the balcony would look much better on the top floor. So he follows your instructions and swaps out the floors, they’re all identical anyways.
When he puts it together, the balcony, which is now at the top, causes the whole tower to fall over.
You redesign the tower so bottom floors can’t go near the top, and balconies can only be attached to bottom floors.
That’s basically what happens. A user finds some use case that nobody thought of before the app was released and that use case is not properly handled.
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