Limits of SQLite WAL Autocheckpoint Threshold on Read‑Only Query Consistency

Goal: Determine how the SQLite WAL autocheckpoint threshold influences the visibility of committed writes to read‑only connections when the write‑ahead log grows beyond the configured limit.

Uncertainty: The automatic checkpoint timing varies between SQLite releases, and it is unclear whether a read‑only transaction can see data that has been partially checkpointed or only up to the last fully completed checkpoint. Adjusting the threshold with PRAGMA wal_autocheckpoint may change the maximum staleness observable by readers, but the exact relationship across versions remains unspecified.

Questions:

• Does a read‑only connection observe only the state of the main database after a checkpoint finishes, or can it see pages that have been copied during an ongoing checkpoint?
• How does changing the wal_autocheckpoint value affect the upper bound on how stale a read‑only transaction can become under heavy write load?
• Are there version‑dependent differences in this behavior that applications must account for when relying on predictable read‑only snapshots?