Quick software engineering explainers for things you should've googled by now
Joined December 2025
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272 Photos and videos
Jun 12
Most engineers can recite the seven OSI layers. Naming which protocols actually live at each one is where it gets fuzzy.
Here’s the full map, layer by layer.
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Jun 11
Your new colleague, a security expert, swears this admin endpoint is bulletproof: the JWT is issued by the server, and the code explicitly checks the payload for the admin role.
Now it's in production, and attackers are making themselves admins. What's wrong with it?
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Jun 9
Why do array indexes start at 0?
It's one of those things most developers just accept without thinking twice. The reason comes down to how arrays are actually stored in memory.
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Jun 8
TCP is reliable, UDP is fast. But why? It comes down to how each handles a lost packet.
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Jun 3
git tags and git branches both point at a commit. So how are they different?
git tags → stay on the same commit
git branches → move to the newest commit
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Jun 2
Quick SQL gotcha: there's an index on created_at, the query filters by created_at, and yet it's still scanning every row.
The property it's missing: sargable
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Jun 1
If Redis stores everything in memory, what happens when it restarts?
Depends on which persistence modes are enabled. Redis has two:
→ RDB: periodic snapshots written to disk
→ AOF: an append-only log of every write
Both can run at the same time.
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May 28
Redis is the reflex answer to “we need a cache,” but a lot of setups never touch the features that separate it from Memcached. Worth knowing what those are before defaulting to it.
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May 28
Classic pagination bug: a product search feels instant on the first few pages, then gets slower the deeper it goes. A few hundred pages in, response times stretch into seconds and CPU usage goes up. OFFSET is the culprit, and the fix is a one-line change to the query.
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May 27
A simplistic mental model
May 26
JUST IN: Uber’s COO says heavy AI spending is getting harder to justify, as higher token usage fails to show a clear payoff in consumer features.
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May 27
/users/verified vs /users?verified=true. Two URLs that handle the same need. Picking the right one comes down to a single question about what verified actually is.
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May 26
Auto-increment IDs are simple: take the last one, add 1.
That model breaks the moment two services need to do it independently.
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May 24
6/ One shot per post.
Two pre-scoring filters drop anything a user has already seen or already been served in the current session.
x.com/The_HappyPath/status/2…
May 23
Everyone has had a post on X stop the scroll, then lost it to a tab switch or a refresh. No amount of searching brings it back.
The For You pipeline has a reason for that.
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May 24
A feed that looks like magic from the outside is six well-named stages running in order. Every surprising behavior in the For You feed has a place in that diagram.
Full repo: github.com/xai-org/x-algorit…
Follow @The_HappyPath for more quick tech explainers
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May 23
Everyone has had a post on X stop the scroll, then lost it to a tab switch or a refresh. No amount of searching brings it back.
The For You pipeline has a reason for that.
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