Persist attachment state per record during sync passes#3
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Pull request overview
This PR reduces attachment-sync contention by avoiding holding the attachment context mutex for an entire sync pass, and by persisting progress incrementally (per attachment) so completed transfers aren’t lost on interruption.
Changes:
- Add a pass-level lock and refactor
RunSyncPassAsyncto acquire the attachment context only for specific reads/writes. - Update attachment processing to persist each state change immediately after its transfer completes.
- Thread cancellation through
SyncStorageAsync/RunSyncPassAsyncso cancellation is observed between records.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| PowerSync/PowerSync.Common/Attachments/SyncingService.cs | Refactors sync pass execution and per-attachment persistence to reduce long mutex holds and improve progress durability. |
| PowerSync/PowerSync.Common/Attachments/AttachmentQueue.cs | Plumbs a CancellationToken through the public API for running an on-demand sync pass. |
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RunSyncPassAsyncheld the attachment context mutex for the entire pass and saved all state changes in one batch at the end. On a large queue, a single pass starved every other queue operation for its duration, plus any interruption discarded the progress of every completed transfer.The context is now acquired only for table reads and writes, and each attachment is persisted as soon as its transfer completes, matching the JS & Dart helpers.