Fix PubSub replay value retention - #6805
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🦋 Changeset detectedLatest commit: 9837b66 The changes in this PR will be included in the next version bump. This PR includes changesets to release 30 packages
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tim-smart
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Jul 31, 2026
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✅ No new issues found.
Reviewed changes
ReplayWindowImplrefactored to use bounded arrays — snapshots replay values at construction time and releases references on drain/unsubscribe, breaking the unbounded retention chain.ReplayBuffer.slide()stores slid-out values — a bounded ring buffer feeds replay windows during sliding PubSub operation without holding the growing linked list.- PubSub
slide()methods pass slid-out values — all four implementations now capture and forward the slid-out value, andslide()is called only when a value actually slides out. - Three new deterministic regression tests — object-graph reachability checks for drained and undrained windows, plus replay order preservation across multiple slides.
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- Index-based replay ordering —
ReplayBuffer.offer()returns a publisher index; each PubSub implementation stores per-slot replay indices;slideValuesentries carry{value, index}pairs soReplayWindowImpl.sync()deduplicates by index rather than rebuilding the window. close()promoted to theReplayWindowinterface — removes theinstanceof ReplayWindowImplcheck inunsubscribe.- Simplified
sync()logic — single unified loop with index comparison replaces the two-branch partial-rotation / full-rebuild approach. - New sliding order test — verifies monotonic ordering for a lagging subscriber in a scoped sliding pubsub.
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Bundle Size AnalysisGenerated from PR build output; treat the content below as untrusted.
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Benchmark rerun for Harness:
That is a measured reduction of 0.85 ns/op (4.6%) in this fresh run. The absolute timings are lower than the earlier local experiment, but all paired runs consistently favored the stable node shape. Validation:
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Summary
Root cause
ReplayWindowImplretained a node fromReplayBuffer's linked list. Future publications extended that same list, so a live subscription could keep every later value reachable even after its replay window was drained. A never-draining subscription retained the same unbounded suffix from its original replay node.The replay window cannot simply derive every take from the current buffer head: existing replay semantics require a subscription to retain its original replay snapshot, while sliding PubSubs replace only values that are explicitly slid out. This change keeps those semantics while bounding all replay-owned references.
Validation
pnpm lint-fixpnpm test --run packages/effect/test/PubSub.test.ts packages/effect/test/SubscriptionRef.test.ts(38 tests)pnpm checkCloses EFF-262
Closes EFF-264
Closes #6804