Elements written per key inserted, 16,384 random keys

Elements written per key inserted, 16,384 random keys

The same 16,384 insertions into an in-place B-tree and into a log-structured store at four size ratios. The B-tree dirties one leaf per key and that leaf is evicted before it is touched again, so it writes a whole block — 49 elements — for each key. The log-structured store writes each key once per level it passes through and writes in whole blocks, so it moves 2.0 elements per key at T = 4. Neither number appears in any operation count, and the second structure exists entirely because of the first.

Drawn at 700 × 310, wide on the page. Everything above is what write-amp returns with no arguments; the caption is the generator's own, computed from the numbers in the drawing rather than written beside it.

15 essays call write-amp. 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.