Windows 8 Search API Paging: Ordering and StartIndex Reliability

Answer Summary

The Windows 8 Search API does not provide a guaranteed stable order for paged results, and StartIndex is largely ignored in the original Windows 8 release. Windows 8.1 respects the property, but developers targeting Windows 8 must treat offset‑based paging as unreliable when the index can change.

Question 1: Stable ordering?

Confirmed fact (per research): The API does not guarantee a stable ordering of results across separate paged queries; the order may change if the underlying index is updated between calls.

Likely explanation: The search indexer rebuilds or updates its internal ranking as items are added, removed, or modified, which can alter the sequence returned for the same StartIndex/MaxResults pair.

Question 2: Behavior when StartIndex exceeds total matches (Windows 8 only)?

Confirmed fact: Setting StartIndex to a value greater than the number of matching items typically returns an empty result set (no items) rather than throwing an exception.

Likely explanation: The API treats the request as a slice beyond the data length, similar to requesting a range past the end of an array, and therefore yields zero results.

Question 3: Best‑practice pattern to avoid duplicates or missing items?

Confirmed fact: Relying solely on StartIndex for pagination can cause duplicated entries or gaps when the index changes between requests.

Recommended steps:

1. Define a stable, unique sort key (e.g., System.ItemName or a combination of System.ItemDateModified and System.ItemKey).
2. Set QueryOptions.SortBy to that key so the server returns results in a deterministic order.
3. After each page, record the last sort‑key value seen.
4. For the next request, add a filter that excludes items with sort‑key values ≤ the last seen value (or use a StartIndex of zero and rely on the filter to skip already‑seen items).
5. Execute the full query with the same MaxResults and apply the filter client‑side; the server’s stable sort guarantees you receive the next contiguous slice without duplicates or gaps.

Alternative (if stable sorting cannot be enforced): Capture the total count from the initial query, request contiguous slices with StartIndex/MaxResults, then deduplicate or fill gaps in the application layer, accepting occasional duplicates or missing items when the index mutates.

Missing diagnostic detail that could change the recommendation: Can you set QueryOptions.SortBy to a stable, unique property on your target Windows 8 system? If not, the client‑side filter approach (step 5) is required.