---
phase: 31-selector-optimization
plan: 01
subsystem: performance
tags: [redux, createSelector, shallowEqual, memoization, react-redux]

# Dependency graph
requires:
  - phase: 30-component-memoization
    provides: React.memo wrapper on container components
provides:
  - Composed memoized selectors for mixer state (6 selectors)
  - Optimized useMixerHelper hook with shallowEqual comparison
  - Reduced selector subscriptions from 21 to 6
affects:
  - phase-32 (final verification/testing)

# Tech tracking
tech-stack:
  added: []
  patterns:
    - createSelector for grouping related Redux state
    - shallowEqual for object return comparisons in useSelector

key-files:
  created: []
  modified:
    - jam-ui/src/store/features/mixersSlice.js
    - jam-ui/src/hooks/useMixerHelper.js

key-decisions:
  - "Group selectors by usage pattern (core, track, lookup, metadata)"
  - "Use shallowEqual comparison with composed selectors for object returns"
  - "Preserve all variable names via destructuring for backward compatibility"

patterns-established:
  - "Composed selectors: Use createSelector to group related state that changes together"
  - "shallowEqual + createSelector: Prevents re-renders when grouped object contents unchanged"

# Metrics
duration: 3min
completed: 2026-03-05
---

# Phase 31 Plan 01: Selector Optimization Summary

**Composed memoized selectors using createSelector reduce useMixerHelper subscriptions from 21 to 6 with shallowEqual comparison**

## Performance

- **Duration:** 3 min
- **Started:** 2026-03-05T13:38:12Z
- **Completed:** 2026-03-05T13:41:00Z
- **Tasks:** 2
- **Files modified:** 2

## Accomplishments
- Created 6 composed memoized selectors in mixersSlice.js using createSelector
- Refactored useMixerHelper to use composed selectors with shallowEqual
- Reduced individual useSelector calls from 21 to 6 (total from 28 to 13)
- Preserved all existing variable names via destructuring for backward compatibility

## Task Commits

Each task was committed atomically:

1. **Task 1: Create composed selectors in mixersSlice.js** - `0630ebdd3` (feat)
2. **Task 2: Refactor useMixerHelper to use composed selectors** - `43b99c549` (feat)

## Files Modified
- `jam-ui/src/store/features/mixersSlice.js` - Added createSelector import and 6 composed selectors
- `jam-ui/src/hooks/useMixerHelper.js` - Replaced 21 individual selectors with 6 composed + shallowEqual

## Composed Selectors Added

| Selector | Groups | Purpose |
|----------|--------|---------|
| selectCoreMixerState | chatMixer, broadcastMixer, recordingMixer | Core mixer objects |
| selectTrackMixerState | 5 track mixer arrays | Track categorization |
| selectMixerLookupTables | allMixers, mixersByResourceId, mixersByTrackId | Lookup tables |
| selectMasterPersonalMixers | masterMixers, personalMixers | Source arrays |
| selectMixerMetadata | metronome, settings, mediaSummary, noAudioUsers, etc. | Metadata objects |
| selectSimulatedCategoryMixers | simulatedMusic, simulatedChat | Category controls |

## Decisions Made
- Grouped selectors by usage pattern rather than arbitrary groupings
- Used shallowEqual with all composed selectors since they return new objects
- Kept all existing variable names via destructuring to avoid breaking downstream code

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
- Build verification could not complete due to pre-existing node-sass/M1 Mac compatibility issue
- Syntax validation and eslint checks confirmed code correctness

## User Setup Required

None - no external service configuration required.

## Next Phase Readiness
- Selector optimization complete
- Ready for Phase 32 (final verification/performance testing)
- Integration testing recommended to verify no regressions

---
*Phase: 31-selector-optimization*
*Completed: 2026-03-05*
