Architecture — Export & Sessions DB

Part of the architecture corpus (index). Read this file in full before touching CSV/MDF4 export, the Sessions database, or replay.

Export Architecture & Sessions DB (Pro)

• DataModel::ExportSchema (ExportSchema.h): shared column layout. buildExportSchema(frame) produces sorted columns + uniqueIdToColumnIndex map. CSV and MDF4 export raw + transformed.
• Session DB lives in app/src/Sessions/ (NOT app/src/SQLite/):
  • Sessions::DatabaseManager — singleton owning the open .db; backs app/qml/DatabaseExplorer/.
  • Sessions::Export (Sessions/Export.h/.cpp): FrameConsumer-based; tables sessions/columns/readings/raw_bytes/table_snapshots; second lock-free queue for raw bytes via ConnectionManager::onRawDataReceived. WAL mode, batch transactions.
  • Sessions::Player: replays a stored session through the FrameBuilder pipeline using the final (post-transform) reading columns, with a uid->cell replay column map installed via FrameBuilder::setReplayColumnMap (same mechanism as MDF4). All three players count as final-value players (SerialStudio::isFinalValuePlayerOpen), so per-dataset transforms never re-run during playback — they read live inputs (data tables) that don't exist then. Raw columns are only a fallback for pre-final-column session files.
  • Replay payload rows are RFC-4180 quoted: players synthesize rows with DataModel::joinReplayRow and FrameBuilder splits them with splitReplayChannels / splitReplayRow (FrameParserPipeline.h), so string values containing commas/quotes survive replay. The live QuickPlot split (splitQuickPlotChannels) is untouched — the quote-aware splitter only runs when m_playerOpen is set.
  • table_snapshots capture: Sessions::Export::captureTableSnapshots (main thread, TimerEvents::timeout1Hz) diffs FrameBuilder::tableStore().snapshot() (skipping the __datasets__ system table) against the last tick and enqueues changed registers to the worker, which batches them into table_snapshots. Replay does NOT need them (finals are replayed); they exist for post-hoc inspection.
  • Per-sample tables use surrogate rowid PKs (reading_id, raw_id, snapshot_id INTEGER PRIMARY KEY AUTOINCREMENT) with covering indexes on (session_id, unique_id, timestamp_ns) and (session_id, timestamp_ns). Use plain INSERT — never INSERT OR IGNORE — timestamp_ns collisions are routine.
  • Break ts ties with reading_id in ORDER BY / MIN/MAX subqueries. DISTINCT timestamp_ns stats undercount on collisions.