query: RecentCreates snapshot COW and head RCU - #261
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August 25, 2026 18:23
snapshot cloned the pending HashMap on every stamp. Hold pending as Arc<LiveMap>: snapshot Arc-clones; note/filter make_mut; empty maps reuse one process Arc. Closes algo-review P17.
publish_layer/drop_ready/drop_from/expire_through stored a chain built from a stale load_full. CAS the ArcSwap head and retry; a lost drop_from vs publish cannot restore dropped heights. Closes algo-review Q-M2.
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What
RecentCreates::snapshotno longer clones the pending HashMap on every stamp. Pending is a COWArc<LiveMap>: snapshot Arc-clones;note*/filter_pendingmake_mut; empty pending reuses one process Arc.Head publish/drop is RCU.
publish_layer/drop_ready/drop_from/expire_throughCAS-splice vialayer_chain::{cas_head,rcu_head}and retry on a lost CAS. A staleload_fullthenstorecannot restoredrop_fromheights.Why
Stamp snapshots were copying the pending map (pins included) every wave (algo-review P17). Head update was load-then-store, safe only if the write thread was the sole mutator — unenforced, and
drop_fromis on the reorg path (Q-M2).Algo-review
Closes P17 and Q-M2 by deleting those rows in the same commits as the fixes.
Independent of
confirm/wire-plan-batch.Tests
snapshot()calls with nonote*/publish_layer/drop_*share pending byArc::ptr_eqnote_pinsdoes not see the note; after does;create_pinArc-clones the pincas_headagainst a staledrop_fromhead fails; retry prepends onto the current head; dropped height stays gone