Backend & systems·Data modelling and storage engines
you wrote one kilobyte and the disk did fifteen kilobytes of work, because the row is in three indexes and compaction will rewrite it twice.
Write amplification
The ratio of physical bytes written to logical bytes you asked to store. It comes from index maintenance, write-ahead logging, page-level rewrites and background compaction. It is the reason adding "just one more index" degrades write latency, and the reason an SSD wears out faster than the raw data volume suggests.