db/kv/membatchwithdb: restrict overlays to the pure-Go memStore backing - #22534
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db/kv/membatchwithdb: restrict overlays to the pure-Go memStore backing#22534yperbasis wants to merge 1 commit into
yperbasis wants to merge 1 commit into
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Split out of #21293. Shared-tx read views are safe under a concurrent parent Close only because memStore's Rollback/Close are no-ops on the data; typing memTx as *memStore enforces that backing. Remove the unused MDBX-backed constructor, whose write tx pins an OS thread and would invalidate cursors mid-iteration.
This was referenced Jul 16, 2026
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Split out of #21293 (
FcuBackgroundCommitgroundwork).Shared-tx overlay read views (
MemoryMutation.NewReadView/NewTemporalReadView) are safe under a concurrent parentCloseonly on the pure-GomemStorebacking, whoseRollback/Closeare no-ops on the data — that is what lets a background-commit goroutine close the published overlay while RPC readers still iterate views. This PR makes the invariant structural instead of conventional:MemoryMutation.memTxis typed*memStore(waskv.RwTx), so an overlay cannot be constructed on a backing whoseRollbackinvalidates cursors.NewMemoryBatchMDBX(the MDBX-backed constructor, unused) is removed: its write tx pins the goroutine to an OS thread and itsRollbackdestroys the data under live read views — exactly the construction the invariant forbids.newReadViewMut, with pointers fromMemoryMutation.Rollback,SharedDomains.Close, andFilters.WithOverlay/WithTemporalOverlay(the read-view producers/consumers that rely on it).