Settings
Everything here is stored in this browser and nowhere else. There is no account to attach it to and no server holding a copy — which is why the export button below is the only backup that exists.
Appearance
Theme
System follows your operating system while the tab is open. The palette is defined twice — once for each theme — and never generated from the other.
Engine
Dataset scale
Small is a hundred or so rows, sized for reading a result set. Realistic is a million, generated lazily from a seed, and it is the only size where a cost mistake actually hurts.
Explain every query
Runs EXPLAIN alongside each playground query without being asked. Off by default in drills, where reaching for the plan yourself is part of what is being measured.
Editor
Font size
The query editor only. Lesson prose has its own scale and does not follow this.
Line numbers
Parse errors are reported with a line and column, so the numbers are worth having when a query grows past a few lines.
The planner
The cost model’s constants. These are a model, not milliseconds — they do not predict your production database. What they are good for is comparison, and turning one changes every plan in the app at once.
random_page_cost
What a page fetched at random costs against one read in sequence. The default of 4 describes a spinning disk; on an SSD it is closer to 1, and almost nobody changes it. Set it to 1 and watch the index scans appear.
work_mem
How much a sort or a hash may hold before it has to batch. Lower it and watch a hash join report more batches and a sort start paying for pages.
Your data
- Exercises
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- Solved
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- Attempts
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- Stored
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This browser is not storing anything. The session works, but nothing will survive the tab.