pub static UNIQ_PROBE_CALLS: AtomicU64Expand description
v7.39 (round 166) — probe idx for a live row whose collated key
equals key (the fold of the row being written). Returns the row
position of the first conflicting live row. fold recomputes the
collated key of a candidate row so collation / bpchar semantics stay
byte-identical with the HashSet path; tombstoned rows are skipped the
same way; Cold locators are skipped because the fold path only ever
scanned hot rows.
v7.39 (round 492) — how many locators the uniqueness probe walks, and
how many probes there are.
The round-491 profile of delete_reinsert_1k put this function at
8.4 % of the connection thread. A BTree index carries one locator per
row VERSION, and this shape deletes and re-inserts the same ids over
and over, so the suspicion is that each probe walks every dead version
under its key. Round 490 fixed exactly that shape of defect on the
seek side — which is why this is a counter and not an assumption.