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One Contains Call, 375 Million Comparisons

By Sukhpinder Singh · DEV Community · 11/2/2026

A nightly reconciliation job that cross-checks incoming orders against a list of active SKUs crept from "instant" to "noticeable," and the profiler pointed straight at a line I'd have sworn was free. It was a membership check. One Contains . The kind of thing you write without thinking because it…

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