Migrating To Checkpoints

Migrating to Checkpoints

Update existing createSync() code to use checkpoints. Preserve provider behavior first; only change the progress/resume mechanism and the deletion handling needed to make checkpointing correct.

Scope

• This skill assumes Zero YAML TypeScript syncs. If nango.yaml still defines the sync, suggest migrating to Zero YAML as a next step before or alongside the checkpoint migration. Mention the migrating-to-zero-yaml skill, suggest npx skills add https://github.com/NangoHQ/skills --skill migrating-to-zero-yaml if it is not installed, and link the docs: https://nango.dev/docs/implementation-guides/platform/migrations/migrate-to-zero-yaml.
• Prefer one sync at a time when a repo has many providers.

Gotchas

• Always call saveCheckpoint() immediately after every successful batchSave() (and after batchUpdate() / batchDelete() when those advance progress). This is required inside pagination loops (for await over nango.paginate, manual cursor/offset loops, nested fetches)—not only once at the end of exec. Saving only after a helper returns or only at the end of exec leaves no durable progress if the run fails mid-pagination.
• Do not guard saveCheckpoint() with "more pages remain." A pattern like if (nextCursor) { await nango.saveCheckpoint(...) } skips the call on the terminal page. If the whole dataset fits on that first page, no checkpoint row is ever written, and clearCheckpoint() then fails with checkpoint_conflict ("Checkpoint has been updated since last read") — the same error a real concurrent write would produce, because clearCheckpoint() is optimistic-locked and a delete matching zero rows is rejected identically. Always save the checkpoint on every page, including the last, before clearing it.
• Do not add a checkpoint that is only saved. The next run must use it in provider request params or pagination/resume state.
• Use flat checkpoint objects only: string, number, or boolean values. Store dates as ISO strings; do not save Date objects, arrays, or nested objects.
• The first run after deployment has no checkpoint yet, so it behaves like an initial sync and may take longer than later incremental runs. Tell the customer when this matters.
• Incremental changed-only syncs must not use trackDeletesStart() / trackDeletesEnd(). Those endpoints omit unchanged rows, so Nango would mark unchanged records as deleted.

Inventory

Search for legacy and partial checkpoint patterns:

rg -n "lastSyncDate|syncType:\s*['\"]incremental|deleteRecordsFromPreviousExecutions|trackDeletes:|track_deletes|getCheckpoint|saveCheckpoint|clearCheckpoint" .

For each sync, identify:

• Existing lower bound or resume marker: updated_at, modified_since, changed-records endpoint cursor, page token, offset/page, since_id, etc.
• Whether the provider request returns changed rows only or walks the full dataset.
• Pagination shape and whether progress can be saved after each page.
• Model names passed to batchSave, batchUpdate, and batchDelete.
• Delete strategy: explicit deleted-record endpoint/tombstones/webhooks, full-refresh diffing, or no safe delete signal.

Choose the Checkpoint

• Timestamp lower bound: z.object({ updated_after: z.string() }).
• Cursor or changed-record feed: z.object({ cursor: z.string() }).
• Page/offset resume: z.object({ page: z.number() }) or z.object({ offset: z.number() }).
• Composite resume: combine flat primitives, for example z.object({ updated_after: z.string(), page_token: z.string().optional() }).
• Full refresh resilience: save a cursor/page checkpoint during the run and call clearCheckpoint() only after the full dataset was fetched and saved successfully.

If the provider cannot filter changes and cannot resume pagination, do not force checkpoints. State the provider limitation and keep or convert to an explicitly justified full refresh.

Migration Steps

1. Add a named checkpoint schema near the sync and pass it to createSync():

const CheckpointSchema = z.object({
  updated_after: z.string(),
});

export default createSync({
  description: "Sync contacts",
  frequency: "every hour",
  checkpoint: CheckpointSchema,
  models: { Contact },
  exec: async (nango) => {
    // ...
  },
});

2. Remove syncType: 'incremental' from incremental migrations. The checkpoint field replaces that legacy signal.

3. Replace nango.lastSyncDate reads with await nango.getCheckpoint() and use the checkpoint in the provider request:

const checkpoint = await nango.getCheckpoint();

const response = await nango.get({
  endpoint: "/contacts",
  params: {
    ...(checkpoint?.updated_after && {
      updated_after: checkpoint.updated_after,
    }),
  },
  retries: 3,
});

4. After every batchSave(), call saveCheckpoint() in the same loop iteration—including inside nango.paginate and any extracted pagination helper. Pair them; do not defer checkpoint writes to the end of exec.

const contacts = response.data.items.map(mapContact);
await nango.batchSave(contacts, "Contact");

if (contacts.length > 0) {
  const lastContact = contacts[contacts.length - 1]!;
  await nango.saveCheckpoint({ updated_after: lastContact.updated_at });
}

Paginated sync:

for await (const page of nango.paginate<Item>(config)) {
  const records = page.map(mapRecord);
  await nango.batchSave(records, "Contact");
  await nango.saveCheckpoint({ updated_after: latestTimestamp(records) });
}

Invalid: await getAndSaveUsers(nango) that only calls batchSave inside the loop, then saveCheckpoint once in exec after the helper returns.

5. For timestamp checkpoints, prefer the provider record's sorted last-modified value. If records can share the same timestamp or the API cannot sort stably, use a composite checkpoint with a provider cursor/page token or a tie-breaker field such as last_id.

6. Do not accumulate all records in memory just to save one final checkpoint. Process, batchSave, and saveCheckpoint page by page.

Full Refresh With Checkpoints

Use this only when the API cannot return changed rows but can resume pagination. The checkpoint is for failure recovery, not incremental filtering — and it is mandatory, not optional. Nango syncs run inside a time-limited execution window. Without a checkpoint, a full refresh that does not finish in that window restarts from page 1 on the next run, re-fetching the same early pages every time and never reaching the rest of the dataset.

• Read the saved cursor/page before fetching.
• Call trackDeletesStart() on every execution of the refresh. It is safe to call repeatedly — it will not overwrite the start of a delete-tracking window that a prior execution of the same logical refresh already opened.
• Start pagination from the saved cursor/page when the checkpoint is present.
• After each successful batchSave(), call saveCheckpoint() with the next cursor/page (same loop body—never only at the end of exec) — including on the last page, not only when another page remains.
• Call clearCheckpoint() only after the last page is saved. Saving every processed page, including the last, guarantees that the normal page-processing path has a checkpoint row to clear. If a distinct path creates no checkpoint at all (for example, it processes no pages), do not call clearCheckpoint() on that path; it throws checkpoint_conflict at runtime. This is not a substitute for saving the last page.
• Call trackDeletesEnd() only after that clearCheckpoint(), so it fires exactly once, in the execution that actually finished the full dataset.
• On the next scheduled run, a cleared checkpoint makes the sync start from the beginning again.

Delete Handling

• If the provider exposes deleted records, tombstones, or delete webhooks, call batchDelete() for those IDs using the same checkpoint window.
• If delete detection requires comparing the full dataset, use full refresh: call trackDeletesStart('Model') before fetching/saving and trackDeletesEnd('Model') only after the full dataset is saved and the checkpoint is cleared.
• In a checkpointed full refresh that spans multiple executions, trackDeletesStart() can run at the start of each execution — it is safe/idempotent and will not overwrite the start of an already-open window. trackDeletesEnd() belongs only in the execution that completes the full refresh and clears the checkpoint.
• Remove deleteRecordsFromPreviousExecutions(). It is incompatible with checkpointed syncs.

Test

Run the local validation loop from the Nango project root:

nango compile
nango dryrun <sync-name> <connection-id> --validate -e dev --no-interactive --auto-confirm
nango dryrun <sync-name> <connection-id> --validate -e dev --no-interactive --auto-confirm --checkpoint '{"updated_after":"2024-06-01T00:00:00Z"}'

Use --metadata when the sync needs metadata, tailor the --checkpoint payload to the schema, and run the repo's existing test suite if one exists.

Final Checklist

• No remaining nango.lastSyncDate references in migrated syncs
• No syncType: 'incremental' left for checkpointed incremental syncs
• checkpoint schema exists and uses only flat primitive values
• getCheckpoint() is called before provider requests
• Saved checkpoint changes the next provider request or resume state
• Every batchSave()/batchUpdate()/batchDelete() that advances progress is immediately followed by saveCheckpoint() in the same loop (including inside nango.paginate and pagination helpers—not only once after exec returns)
• Full refresh syncs have a checkpoint schema, resume pagination from it, save it after every page (including the last), and call clearCheckpoint() only after successful completion of the last page
• Full-refresh saveCheckpoint() calls are never guarded by whether another page remains
• Every path that calls clearCheckpoint() has created or resumed a checkpoint; paths that create none do not call it
• Full refresh trackDeletesEnd() runs only after clearCheckpoint(), in the execution that finishes the last page
• Delete handling matches the sync type: batchDelete() for explicit provider deletes, trackDeletesStart/End only for full refresh
• Dryrun was tested with a realistic --checkpoint

Useful Docs

• Checkpoints: https://nango.dev/docs/implementation-guides/use-cases/syncs/checkpoints
• Migration guide: https://nango.dev/docs/implementation-guides/platform/migrations/migrate-to-checkpoints
• Deletion detection: https://nango.dev/docs/implementation-guides/use-cases/syncs/deletion-detection
• Functions SDK reference: https://nango.dev/docs/reference/functions#checkpoints