DEFAULT_MIN_RISE

The p90 presses only this far above its baseline, whatever the factor: a factor alone is relative, and a store whose appends take a millisecond (PostgreSQL on a near network) would press on noise of a millisecond or two, as one of a few milliseconds would on the jitter of a busy pool. Twenty milliseconds is about one more round trip queued on a pool under load, a delay the writes feel.