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SQLite persistence: after two quick writes to one row, the collection briefly shows the state before the second write

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  • Quelque chose ne va pas ?
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Une pull request liée a déjà été fusionnée.

  • #2208 par @KyleAMathews — fusionnée

Évaluation

Difficulté
4/5
Temps estimé
3-5 jours
Accessibilité débutants
48/100
Type d'issue
Bug
Clarté
Plutôt claire
Activité
Active
Stack technique
sqlite, typescript
Domaine
database, databases

Piste de recherche

Start with the persistence and transaction flow described in the issue, especially awaitTxId, applyMutex, pendingSyncedTransactions, and recomputeOptimisticState; the linked reproduction and its README contain the trace and timings. Trace how an update is handled while SQLite still stores the insert's synced transaction, then verify that the collection never shows an older state after awaitTxId resolves. The issue does not identify source files or tests, so locating the relevant code and adding a regression test will take familiarity with the project.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Description

  • I've validated the bug against the latest version of DB packages

Describe the bug

An Electric collection with persistedCollectionOptions inserts a row and updates it right away. Both handlers await awaitTxId. After the update is confirmed, the collection shows the pre-update state for 10–30 ms, then the updated state again. Without persistence, this never happens.

I hit this in a shopping list app. A user adds an item and ticks it off. The tick disappears for a moment, then comes back. An action that runs during that gap reads the old state: "clear bought items" saw the item as not bought and left it on the list. With 10× CPU throttling, the gap reached 263 ms in my app.

To Reproduce

Repro: https://github.com/daniel-fahl/tanstack-db-flicker-repro (StackBlitz). It needs no backend: a fake Electric server runs in the page.

  1. Open the repro.
  2. Click Add and tick 30 times. Each run inserts a todo and updates done to true without waiting in between.
  3. See the result: 30 of 30 runs flicker. Each run logs the states the collection showed, for example missing → unticked → ticked → unticked +24 ms → ticked +41 ms.
  4. Switch to Control (?persistence=off) and run again: 0 of 30 flicker.

Expected behavior

When awaitTxId(txid) resolves and the handler returns, the collection never shows a state older than that write.

Screenshots

None. The repro's log shows every state with its timing.

Desktop (please complete the following information):

  • OS: macOS; my app's CI also hits it on Ubuntu (GitHub Actions ubuntu-latest)
  • Browser: Chromium, via Playwright
  • Version: Chromium as bundled with @playwright/test 1.64

Smartphone (please complete the following information):

Not tested on a device yet. 10× CPU throttling stands in for a slow phone.

Additional context

Versions: @tanstack/db 0.15.1, @tanstack/electric-db-collection 0.6.2, @tanstack/browser-db-sqlite-persistence 0.2.36, @tanstack/offline-transactions 1.1.3, @electric-sql/client 1.5.28. The same result on @tanstack/db 0.15.0 with @tanstack/electric-db-collection 0.6.1, and on 0.13.0 with 0.5.9.

Cause, in brief: the update's txid arrives while SQLite still stores the insert's synced transaction. awaitTxId resolves, but the update's synced transaction waits for applyMutex, so it is not in pendingSyncedTransactions yet. When onUpdate returns, recomputeOptimisticState finds no committed pending synced transaction for the key and drops the optimistic row. The repro's README has the full trace with timings from my app.

Possible fix: I am not sure where it belongs. Two ideas:

  • awaitTxId resolves only once the synced transaction for that txid has reached the collection, at least as a committed pending transaction.
  • recomputeOptimisticState also keeps the optimistic row while a synced transaction for that key still waits on persistence.

Waiting until the rows are fully applied would deadlock: the collection holds back synced rows while a transaction is persisting, and the handler's own transaction is persisting while it awaits the txid.

My workaround: the handler waits 150 ms after awaitTxId resolves. That was the shortest wait that removed every flicker in my app at 10× CPU throttling.

Related: #2120 may be related. It covers changes that progressive mode applies and confirms during the background full sync.

Langage dominant
TypeScript
Étoiles
3.9k
Forks
277
Merge moyen
18 h 12 min
PR mergées (30 j)
229

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