Under default adaptive retention, every flush() recomputed total history
bytes by walking EVERY committed generation's delta — O(all generations)
with disk re-reads past the 4096-entry delta-cache bound. On a production
brain with 70,000+ accumulated generations this turned every write into a
full-tail scan (60-100s writes, escalating with history growth), even
though the free-RAM budget never tripped and nothing was ever reclaimed
(SELF-GENERATIONS-GROWTH).
historyBytes() now maintains a running total: seeded by one walk on first
use, then updated incrementally at both commit paths (+bytes) and the
compaction reclaim loop (−bytes), dropped on reopenAfterRestore. The
adaptive retention check on every flush is O(1). Invariant regression-
pinned: running total ≡ fresh walk through transact commits, single-op
group commits, and compaction.
New brain.historyStats() (exported HistoryStats): read-only generation
count / bytes / generation+timestamp range / horizon / retention mode /
effective budget — the one-call per-brain fleet audit for retention
exposure.
David Snelling
6207e48b51