What one summary promises, and what the merge of 8 delivers

What one summary promises, and what the merge of 8 delivers

Four quantiles of 20,000 log-normal, σ = 1.2 — a latency distribution values. The promise column is ε times the mass above the quantile, which is what a single high-biased summary at ε = 0.01 is entitled to. The merged column is the rank error a merge of 8 shard summaries actually made. Where the merged error exceeds the promise the row is marked: the merge did not break its OWN bound — which is looser, and compounds up the tree — it broke the one a reader would have been quoted.

Drawn at 700 × 294, wide on the page. Everything above is what merge-quantiles returns with no arguments; the caption is the generator's own, computed from the numbers in the drawing rather than written beside it.

6 essays call merge-quantiles. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about — which is what optcheck and figfill exist to catch.