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#observability

tuckerl.ee

Building thoughtful software with AI.Notes from the systems behind the work.

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Latency panel said p95 and was averaging averages

Rereading my own dashboard rebuild, I found a panel labeled with percentiles that averaged per-window means, plus a handful of smaller labels that promised more than their queries: substring metric picks, ignored temporality, a token total that widened, and seed data the two lanes can't agree on.

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Average stored in a table that adds everything up

A few of my ClickHouse rollups kept an average next to the total, and the summing engine would have added those averages on every merge; now they keep total and count and divide at read time, and the affected rollup keys now include every label they store.