distributed systems
5 minEvent-Time Windows: Watermarks, Late Data, and Correctable Results
Design a minute-level dashboard that tolerates delayed events without treating a watermark as proof that every event arrived.
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19 matching resultsArticles and interview answers
typescript
6 minTypeScript results: distinguish absence, invalid input, and dependency failure
Parse unknown data and use discriminated unions to preserve operational meaning through callers.
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Q&AWhy model missing, invalid, and unavailable as separate TypeScript results?
They require different caller behavior and must not collapse into null.
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Validate unknown runtime data, then preserve outcome meaning in a discriminated union. Exhaustive handling exposes new states during compilation; structural validation does not establish permissions or retry safety.
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Q&AWhat property should a reduce operation have for safe parallel combination?
Associativity and an identity element make regrouping partial results meaningful.
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A parallel reduction may group values differently, so its combine operation should be associative for equivalent results and have a suitable identity value. Floating-point addition can vary slightly with grouping. Avoid reducers with hidden side effects because execution order may not be stable.
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Q&AHow do you confirm and fix an ORM N+1 query?
Count repeated statements per request, then batch-load without changing result cardinality.
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Trace or log normalized SQL for one request and look for the same child lookup repeated once per parent row. Replace the loop with an eager/batch load or a query at the correct grain. Verify query count and returned rows; a broad join can fix round trips while accidentally multiplying results.
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Q&AWhat is the difference between WHERE and HAVING?
WHERE filters input rows before grouping; HAVING filters groups after aggregation.
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Use WHERE to remove rows before GROUP BY, such as excluding inactive employees. Use HAVING to filter aggregate results, such as departments with COUNT(*) greater than five. Moving a condition between them can change both meaning and query work.
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Q&AIs Python map eager or lazy?
In Python 3, map returns an iterator that computes values as it is consumed.
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Python 3 map is lazy: it returns an iterator and evaluates each mapped value as the iterator advances. Convert it to a list only when you need materialized results or repeated traversal. Lazy evaluation saves memory but exceptions may occur later when a consumer iterates.
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Q&AHow are Oracle analytic functions different from GROUP BY?
Analytic functions calculate across a partition while keeping each input row in the result.
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GROUP BY collapses rows into one row per group. An analytic function uses OVER with partition, ordering, and frame rules to calculate a value while preserving row detail. Specify a deterministic ordering and explicit frame for running totals when peer-row behavior would matter.