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When designing a schema for ClickHouse, there are dozens of large and small decisions engineers need to make to design a well-performing solution fit for the problem being solved.
The following documents outline various schemas we have at PostHog, examining why they are designed this way, what are some good parts about them and mistakes that were made.
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Problem and constraints PostHog provides Apps for data imports, exports and transformation purposes. App metrics helps users of apps want to know whether the apps are reliable and have tooling to debug errors. When designing the schema, we needed ingestion of these stats should be as 'cheap' as possible. On the flip side queries against the data did not need to support much beyond time-range filtering. Schema Decision: Store errors in the same table as metrics Error tracking is fundamentally…
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