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Premature optimization in interviews kills more designs than actual bottlenecks. Start simple, scale when requirements force you to, and explain the complexity cost when you do.

You just told your interviewer you'll split into multiple databases. They're now waiting to see if you understand what you're giving up.

How Slack scaled MySQL to 1.5 billion messages a day

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This is the large-blobs pattern. Anytime you're moving big files, get your application server out of the data path. Object storage is purpose-built for this. Your app servers are not.

A user uploads a 4GB video to your app. Your server times out after 30 seconds. Upload fails.

These tools solve real problems at scale, but they also introduce operational complexity. Strong candidates start simple and only add complexity when requirements demand it.

Knowing when NOT to use a pattern separates senior engineers from everyone else. Four advanced techniques that fail interviews when used prematurely.