fix(swift-sdk): make a changeset round linear without giving up atomicity - #4595
fix(swift-sdk): make a changeset round linear without giving up atomicity#4595romchornyi wants to merge 2 commits into
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…e watermark last A changeset round in `PlatformWalletPersistenceHandler` accumulated every row unsaved until `endChangeset`, so each per-row `fetch()` in `upsertUtxo` / `upsertTransaction` re-scanned the whole pending set — O(rows²) per round. On a mixing-heavy wallet the catch-up round after a backward re-walk (thousands of TXO/transaction upserts) turned into minutes of compute on the persistence queue and looked like a hang; sampling put every sample inside SwiftData's pending-merge hashing. Flush `backgroundContext` every 500 applied rows (`noteRowApplied`) so the pending set stays bounded and the round is linear. Because intermediate saves commit rows before the round ends, the `syncedHeight` watermark can no longer be written when the chain changeset arrives: stage it in `deferredSyncedHeights` and apply it immediately before the round's final save. The watermark certifies "every row at or below this height is durable", so it must be the last thing a round commits — a crash mid-round then leaves idempotent rows without an advanced watermark, and the durable re-walk redelivers the remainder. Staged watermarks are dropped on rollback, like the parked payment rows. Measured on the same wallet: the persisted frontier went from stuck at 2,174,999 for 10+ minutes to advancing continuously; a simulator kill mid-round resumed from the last committed watermark and reached the tip with a store that matched the chain.
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ChangesWallet persistence
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The changeset persistence path now uses round-scoped lookups while retaining a single final save for each round. No current merge-blocking risk is identified. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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In
`@packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletPersistenceHandler.swift`:
- Line 178: Update the endChangeset flow around backgroundContext.save() to
preserve atomicChangesets: do not commit the shared changeset context before
every callback succeeds. Coordinate an acknowledged checkpoint with Rust, or
isolate the writes in a transaction that rollback() can undo as one unit,
ensuring callback failure leaves no partial SwiftData changes.
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…a round registry instead of intermediate saves Review (#4595): the intermediate `save()` every 500 rows committed every dirty object in `backgroundContext`, so a callback failing later in the round left those rows committed while `endChangeset` rolled back and reported failure to Rust. That breaks the declared `atomicChangesets` contract, which invitation creation requires — the bit cannot simply be dropped. Replace the intermediate saves with a round-scoped registry. The quadratic cost was never the number of rows but the per-row `fetch()` by txid / outpoint: SwiftData evaluates the predicate against the context's pending changes, hashing the whole unsaved set on every lookup. While a round is open, `lookupTransaction` / `lookupTxo` / `lookupPendingInputs` serve rows this round has fetched or created from dictionaries and fall through to a store-only fetch (`includePendingChanges = false`) on a miss. Every in-round creation of those entities registers itself, so a store-only miss never means "created earlier this round"; rows deleted this round are filtered via `isDeleted`. The registry is reset at `beginChangeset` and after commit or rollback. Outside a round the helpers behave like the plain fetches they replace. One `save()` per round, as before; the deferred-watermark staging is no longer needed and is gone. Same wallet, simulator rescan of the full history with a process kill at height 2,180,000 and a relaunch: persistence kept pace with the scan (~2.0M heights in ~75 s), resumed from the persisted watermark, reached the tip; the store matched the previous run row for row (6,787 transactions, 13,882 TXOs, no duplicates, no stubs, no failed rounds).
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Final validation — GLM Flash + Sol
The round-scoped registry removes the quadratic pending-change scans while preserving a single final save, but its store-only fetches run on the write context and can overwrite staged mutations or deletions with committed snapshots. This data-loss path must be fixed before merge; focused round-level regression coverage should also protect the registry’s bookkeeping contract.
Source: reviewer 1: glm-5.3-flash (agent: phase1-reviewer, role: general); reviewer 2: gpt-5.6-sol (agent: phase2-reviewer, role: general); final verifier: gpt-5.6-sol (agent: sol-verifier, role: final-verifier)
Review provenance
- Phase 1 reviewers (GLM Flash):
glm-5.3-flash— general (completed); agentphase1-reviewer - Fresh verifier (Sol):
gpt-5.6-sol— final-verifier; agentsol-verifier - Phase 2 reviewers (Sol):
gpt-5.6-sol— general (completed); agentphase2-reviewer
🔴 1 blocking | 🟡 1 suggestion(s) | 💬 1 nitpick(s)
1 additional finding(s) omitted (not in diff).
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In `packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletPersistenceHandler.swift`:
- [BLOCKING] packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletPersistenceHandler.swift:189-191: Store-only fetches overwrite staged changes in the write context
`includePendingChanges = false` excludes pending changes from result construction, but fetching through the same `ModelContext` can refresh an already registered model from its committed snapshot. That refresh replaces unsaved scalar values and relationships, and a store-only refetch of a staged deletion can restore `isDeleted` to `false` before this filter runs. This is reachable here because Rust emits address-pool callbacks before the core wallet changeset: `persistAccountAddresses` fetches existing TXOs and stages `txo.coreAddress = row` at lines 3693-3699, but it does not register those TXOs. A later `lookupTxo` registry miss fetches the same object store-only through `backgroundContext`, restoring the committed relationship and silently dropping the backfill before the round’s only `save()`. Perform store queries in a separate read context and resolve their persistent identifiers in `backgroundContext`, or ensure every existing tracked model and tombstoned key is registered before any in-round mutation can precede a store-only lookup.
- [SUGGESTION] packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletPersistenceHandler.swift:162-170: Add round-level regression coverage for registry bookkeeping
Correctness now depends on every in-round creation and first mutation of `PersistentTransaction`, `PersistentTxo`, and `PersistentPendingInput` being represented in the registry because store-only queries cannot merge unsaved inserts safely. Add an in-memory changeset-round test that covers repeated and out-of-order transaction/TXO upserts, an existing row mutated before its first registry lookup, pending-input deletion followed by another lookup, rollback, and registry reset between rounds. This will detect both missing `registerRound*` calls and accidental reuse of committed or rolled-back objects.
- [NITPICK] packages/swift-sdk/Sources/SwiftDashSDK/PlatformWallet/PlatformWalletPersistenceHandler.swift:1926-1929: beginChangeset documentation still claims it is a no-op
`beginChangeset` now resets the round-scoped registry in addition to setting the tag, so the claim that it is a no-op beyond the tag is false. The reset is load-bearing because it prevents models cached by a committed or rolled-back round from being reused in the next round.
| descriptor.includePendingChanges = !inChangeset | ||
| let rows = (try? backgroundContext.fetch(descriptor)) ?? [] | ||
| return inChangeset ? rows.filter { !$0.isDeleted } : rows |
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🔴 Blocking: Store-only fetches overwrite staged changes in the write context
includePendingChanges = false excludes pending changes from result construction, but fetching through the same ModelContext can refresh an already registered model from its committed snapshot. That refresh replaces unsaved scalar values and relationships, and a store-only refetch of a staged deletion can restore isDeleted to false before this filter runs. This is reachable here because Rust emits address-pool callbacks before the core wallet changeset: persistAccountAddresses fetches existing TXOs and stages txo.coreAddress = row at lines 3693-3699, but it does not register those TXOs. A later lookupTxo registry miss fetches the same object store-only through backgroundContext, restoring the committed relationship and silently dropping the backfill before the round’s only save(). Perform store queries in a separate read context and resolve their persistent identifiers in backgroundContext, or ensure every existing tracked model and tombstoned key is registered before any in-round mutation can precede a store-only lookup.
source: ['claude']
| // Instead, while a round is open, lookups go through the registry | ||
| // below: rows this round has fetched or created are served from these | ||
| // dictionaries, and a miss falls through to a STORE-ONLY fetch | ||
| // (`includePendingChanges = false`), which skips the pending-merge and | ||
| // is an index lookup. Correctness rests on one rule — every row of | ||
| // these entities created inside a round is registered at creation, so | ||
| // a store-only miss never means "not created yet this round". Rows | ||
| // deleted this round are filtered out (`isDeleted`), since the store | ||
| // still has them until the save. Outside a round the helpers behave |
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🟡 Suggestion: Add round-level regression coverage for registry bookkeeping
Correctness now depends on every in-round creation and first mutation of PersistentTransaction, PersistentTxo, and PersistentPendingInput being represented in the registry because store-only queries cannot merge unsaved inserts safely. Add an in-memory changeset-round test that covers repeated and out-of-order transaction/TXO upserts, an existing row mutated before its first registry lookup, pending-input deletion followed by another lookup, rollback, and registry reset between rounds. This will detect both missing registerRound* calls and accidental reuse of committed or rolled-back objects.
source: ['claude', 'codex']
3 participants
Issue being fixed or feature implemented
A changeset round in
PlatformWalletPersistenceHandleraccumulated every row unsaved untilendChangeset, so each per-rowfetch()inupsertUtxo/upsertTransactionre-scanned the whole pending set — O(rows²) per round. On a mixing-heavy wallet (~6.7k transactions, ~13.8k TXOs) the catch-up round after a backward re-walk turned into 10+ minutes of compute on the persistence queue and looked like a hang. Sampling the process put every sample inside SwiftData's pending-merge hashing underupsertUtxo. This is the SDK-side half of the large-wallet "sync finished but transactions are missing" reports; the app-side gate is dashpay/dashwallet-ios#1112.What was done?
The quadratic cost is not the number of rows but the per-row
fetch()by txid / outpoint: SwiftData evaluates the predicate against the context's pending changes, hashing the whole unsaved set on every lookup. The round stays ONE SwiftData transaction with onesave()inendChangeset(theatomicChangesetscontract is untouched); what changes is how in-round lookups are answered:roundTransactions,roundTxos,roundPendingInputs): rows this round has fetched or created are served from dictionaries keyed by their immutable identity (txid / outpoint).lookupTransaction/lookupTxo/lookupPendingInputsrun a store-only fetch (FetchDescriptor.includePendingChanges = false), which skips the pending-merge and is an index lookup. Every in-round creation of these entities registers itself (registerRoundTransaction/registerRoundTxo/registerRoundPendingInput), so a store-only miss never means "created earlier this round"; rows deleted this round are filtered viaisDeleted.beginChangesetand after commit or rollback inendChangeset. Outside a round the helpers behave exactly like the plain fetches they replace.upsertTransaction,upsertUtxo(incl. the stub-parent path and pending-input adoption),resolveInputOutpoint,removePendingInputs,markUtxoSpent,markUtxoInstantLocked.History: the first revision used intermediate saves every 500 rows; review pointed out that a later callback failure would then leave committed rows behind a rolled-back round, breaking
atomicChangesets(which invitation creation requires). That approach is replaced, not layered on.Note: #4589 touches the same file (swept-transaction handling); the hunks do not overlap, but whichever lands second needs a trivial rebase.
How Has This Been Tested?
No new unit tests (the handler has no round-level harness; adding one is a follow-up). Manual, same seed throughout (~6.7k transactions, ~13.8k TXOs, CoinJoin-heavy):
gettxoutaudit of every unspent row matched the chain.a2ba48d7(fix(dash-spv): make backward coverage durable by rewinding synced_height instead of sweeping in memory rust-dashcore#1002); the handler change itself does not depend on it.Breaking Changes
None. A round is still a single SwiftData transaction. Reviewer note: correctness of the store-only lookups relies on every in-round creation of
PersistentTransaction/PersistentTxo/PersistentPendingInputgoing through the register helpers; the three constructor sites in this file do.Checklist:
For repository code-owners and collaborators only
Summary by CodeRabbit
Performance
Reliability