persistCounts() was write-through on every count change with no
serialization, and the atomic writer named its temp file with millisecond
granularity. Two persists inside one millisecond shared the temp path: both
wrote it, the first rename consumed it, the second rename found nothing —
ENOENT, roughly 1,500 times a day on a busy production brain, with a full
ledger write per change behind it. No data was lost (the surviving rename
carried a complete ledger and the next change re-persisted), but the race
was real and the write rate absurd.
flushCounts() now runs exactly one persist at a time; requests arriving
during it collapse into one trailing pass that carries the burst's final
state — N changes cost at most two writes. writeFileAtomic() adds a
per-process sequence to the temp name so no two writes can share a path.
Pinned: a 25-change burst → ≤2 ledger writes, zero errors, ledger equal to
memory; parallel real writes land complete; three same-instant atomic
writes own three distinct temp paths.
David Snelling
5e3b343a0e