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Performance Optimizations

Database Indices (v6)

Added indices on task_relationships(parent_id) and task_relationships(child_id). Without these, every getChildren(), getParents(), getRootTasks(), and hasPath() query performed full table scans on task_relationships. With indices, SQLite uses index lookups instead — O(log n) vs O(n).

These are created in both onCreate (fresh installs) and onUpgrade (existing users upgrading to DB version 6).

Transaction Batching

restoreTask() and deleteTaskWithRelationships() now wrap all their DB operations in a single db.transaction(). Benefits:

  • Fewer fsync calls: SQLite commits once at the end instead of after each statement. On Android (flash storage), each fsync can take 10-50ms.
  • Atomicity: If any insert/delete fails, the entire operation rolls back cleanly.
  • Reduced WAL overhead: Single transaction = single WAL frame group instead of N separate ones.

Debug Symbols

Release builds now use --split-debug-info and --obfuscate. The symbols zip is attached to each GitHub release. This allows symbolicating crash stacks and ANR traces from production.

Symbolicating a crash trace

# Download debug-symbols.zip from the GitHub release
unzip debug-symbols.zip -d symbols/

# Symbolicate an Android stack trace
flutter symbolize -i stacktrace.txt -d symbols/

DAG View: Cached Layout

The GraphView widget from the graphview package recomputes all 5 Sugiyama layout phases on every performLayout() call with zero caching — causing ANR on Android for larger graphs. We replaced it with a custom rendering approach:

  • SugiyamaAlgorithm runs once in _computeLayout() (called from initState(), not build())
  • Node positions and edge paths are cached in state fields (_nodePositions, _edgePaths, _graphSize)
  • Rendering uses Stack + Positioned (nodes) + CustomPaint (edges) — pure widget build with zero layout recomputation
  • 1-finger panning enabled (panEnabled: true on InteractiveViewer)
  • Auto-fit-to-screen on load via addPostFrameCallback

Brain Dump Batch Insert

Brain dump (adding multiple tasks at once) previously called addTask() N times sequentially — each triggering a DB insert, relationship insert, full task list reload, auxiliary data queries, and notifyListeners(). Now uses insertTasksBatch() which wraps all inserts in a single transaction, followed by one refresh.

Provider Refresh Consolidation

All navigation methods (loadRootTasks, navigateInto, navigateBack, navigateToLevel, navigateToTask) previously duplicated the "load task list + compute auxiliary data + notify listeners" pattern inline. Now they set parent/stack state and delegate to a single _refreshCurrentList() pipeline.

The two auxiliary queries (started-descendant IDs and blocked-task info) are independent and run concurrently via Future.wait in _loadAuxiliaryData().

UI Rebuild Reduction

  • TaskPickerDialog: The _filtered getter (which sorts/filters all candidates) was being recomputed multiple times per build() call. Now computed once into a local variable.
  • Leaf detail FutureBuilder: getDependencies() was called on every Consumer rebuild, creating a new Future each time. Now cached in state and only recreated when the task ID changes or a dependency mutation occurs.
  • Task list candidate prep: Five methods (_searchTask, _linkExistingTask, _addParentToTask, _moveTask, _addDependencyToTask) each fetched getAllTasks() and getParentNamesMap() sequentially. Now use a shared _fetchCandidateData() helper that runs both concurrently.

DB Mapping Centralization

Repeated maps.map((m) => Task.fromMap(m)).toList() calls across 7 query methods and inline parent-name grouping loops in 2 methods are replaced by shared static helpers (_tasksFromMaps, _parentNamesFromRows).

Archive Label Caching

_archivedLabel() was recomputed per row per rebuild, each calling DateTime.now() and doing date arithmetic. Now labels are precomputed once in _loadData() using a single now/today snapshot and stored in a Map<int, String>.

Back Button ANR Fix

The PopScope handler on TaskListScreen had canPop: false to intercept back presses for in-app hierarchy navigation. When already at root, provider.navigateBack() returns false, and the handler called navigator.maybePop() — which re-triggered onPopInvokedWithResult (since canPop was still false), creating an infinite loop that pegged the CPU at 99% and caused an ANR.

Fix: replaced navigator.maybePop() with SystemNavigator.pop() for the root-level case, which tells Android to close the activity normally. Non-root back presses are unaffected — navigateBack() returns true and the handler exits before reaching that code path.

Future Work

  • Isolate graph layout: The Sugiyama algorithm runs on the main thread. For <200 nodes this is <50ms, but for larger graphs it could cause jank. Moving it to an isolate requires serializable graph objects (the package's Graph/Node types aren't currently serializable).
  • Debounce notifyListeners(): If DB queries are fast (which they should be with indices), this isn't needed. Revisit if profiling shows excessive rebuilds.