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Backend now tracks last-seq as a monotonic high-water mark (survives truncation) and exposes :truncate-through. compaction.sx: persist/compact checkpoints then drops events with seq <= snapshot seq; should-compact?/ maybe-compact give an explicit every-N policy. Determinism: post-compaction replay value == uncompacted full replay. Phase 3 complete, 76/76. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
44 lines
1.6 KiB
Plaintext
44 lines
1.6 KiB
Plaintext
; persist/compaction — once a snapshot subsumes a log prefix, those events are
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; dead weight: replay starts from the snapshot, so events with seq <= the
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; snapshot's seq are never folded again. Compaction checkpoints then truncates
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; that prefix. The seq counter is monotonic (backend high-water mark) so future
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; appends keep climbing — the surviving tail keeps its original seqs and replay
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; from the snapshot still equals a full replay of the pre-compaction log.
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; Policy is explicit: compact when the uncompacted tail reaches `every` events.
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; Requires: lib/persist/snapshot.sx, lib/persist/log.sx.
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; events accumulated since the last snapshot for name
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(define
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persist/uncompacted
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(fn
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(b stream name seed)
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(-
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(persist/last-seq b stream)
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(persist/project-seq (persist/snapshot-load b name seed)))))
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; policy: should we compact yet? tail since snapshot >= every
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(define
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persist/should-compact?
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(fn
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(b stream name every seed)
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(>= (persist/uncompacted b stream name seed) every)))
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; checkpoint then drop the snapshotted prefix; returns the new snapshot state
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(define
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persist/compact
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(fn
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(b stream name step seed)
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(let
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((state (persist/checkpoint b stream name step seed)))
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(begin (persist/truncate b stream (persist/project-seq state)) state))))
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; compact only if the policy fires; always returns the current snapshot state
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(define
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persist/maybe-compact
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(fn
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(b stream name step seed every)
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(if
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(persist/should-compact? b stream name every seed)
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(persist/compact b stream name step seed)
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(persist/snapshot-load b name seed))))
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