# Migration Script Fixes - Summary

## Issues Resolved

### 1. ALTER TABLE IF NOT EXISTS Syntax Error ✅

**Problem:**
```sql
ALTER TABLE users ADD COLUMN IF NOT EXISTS api_key_hash TEXT
```
LibSQL/Turso doesn't support `IF NOT EXISTS` clause in `ALTER TABLE ADD COLUMN` statements, causing syntax error:
```
SQL_PARSE_ERROR: near EXISTS, "None": syntax error at (1, 43)
```

**Solution:**
- **Split into 3 separate migration steps** for better granularity:
  1. Add `api_key_hash` column (Phase 2, Step 10)
  2. Migrate data from old `api_key` to `api_key_hash` (Phase 2, Step 11)
  3. Update index to use new column (Phase 2, Step 12)

- **Implemented column existence check** in migration execution logic:
  ```typescript
  // Check if column exists before attempting ALTER TABLE
  if (sql.includes('ALTER TABLE') && sql.includes('ADD COLUMN')) {
    const columnNameMatch = sql.match(/ADD COLUMN (\w+)/);
    if (columnNameMatch) {
      const columnName = columnNameMatch[1];
      const checkResult = await this.db.execute(
        `SELECT name FROM pragma_table_info('${tableName}') WHERE name = '${columnName}'`
      );

      if (checkResult.rows.length > 0) {
        console.log(`   ⏭️  Column ${columnName} already exists, skipping`);
        continue;
      }
    }
  }
  ```

- **Benefits:**
  - Idempotent migrations - can be run multiple times safely
  - Clear error messages when columns already exist
  - No syntax errors even if column exists

### 2. Missing Composite Indexes ✅

**Problem:**
Schema definition (`src/database/schema.ts`) defines these composite indexes, but they don't exist in the database:
- `idx_memories_user_type` (user_id, memory_type)
- `idx_memories_user_importance` (user_id, importance DESC)

**Solution:**
- **Added new migration step at beginning of Phase 1:**
  ```typescript
  {
    phase: 'Phase 1',
    name: 'Create missing composite memories indexes',
    description: 'Add composite indexes defined in schema but missing from database',
    sql: [
      'CREATE INDEX IF NOT EXISTS idx_memories_user_type ON memories(user_id, memory_type)',
      'CREATE INDEX IF NOT EXISTS idx_memories_user_importance ON memories(user_id, importance DESC)'
    ],
    verify: `
      SELECT COUNT(*) as count
      FROM sqlite_master
      WHERE type='index' AND name IN ('idx_memories_user_type', 'idx_memories_user_importance');
    `,
    rollback: [
      'DROP INDEX IF EXISTS idx_memories_user_type',
      'DROP INDEX IF EXISTS idx_memories_user_importance'
    ]
  }
  ```

- **Updated verification logic** to expect count of 2 for composite index creation:
  ```typescript
  if (step.name.includes('composite memories indexes')) {
    return count === 2;
  }
  ```

## Migration Steps Summary

### Phase 1 (Low-Risk): 10 steps
1. **NEW:** Create missing composite memories indexes
2. Drop unused learned_patterns table
3. Drop learned_patterns indexes
4. Drop redundant entities indexes
5. Drop redundant memories indexes
6. Create optimized memories archived index
7. Drop redundant interactions indexes
8. Create optimized interactions index
9. Drop redundant api_usage_tracking indexes
10. Create optimized api_usage_tracking index

### Phase 2 (Medium-Risk): 3 steps
1. **UPDATED:** Add api_key_hash column to users table
2. **NEW:** Migrate api_key data to api_key_hash
3. **UPDATED:** Update users api_key index

## Testing & Validation

### Dry-Run Test
```bash
npm run migrate:schema:dry-run
```
✅ All 13 migration steps display correctly
✅ No syntax errors
✅ Clear descriptions for each step

### Migration Validation Test
```bash
npm run migrate:schema:test
```
✅ Column existence check logic verified
✅ Pattern matching for ALTER TABLE validated
✅ Current database state inspected
✅ Missing indexes identified

### Build Test
```bash
npm run build
```
✅ TypeScript compilation successful
✅ No type errors
✅ All imports resolved

## Key Improvements

### 1. Idempotency
- Migration can be run multiple times safely
- Column existence checks prevent duplicate column errors
- `IF NOT EXISTS` used for index creation

### 2. Error Handling
- Clear error messages for column conflicts
- Graceful handling of already-migrated databases
- Verification steps for each migration

### 3. Granularity
- Single-responsibility steps
- Easier to debug failures
- Better rollback capabilities

### 4. Documentation
- Clear descriptions for each step
- Phase organization (Low-Risk vs Medium-Risk)
- Comprehensive verification queries

## Usage Examples

### Run all migrations
```bash
npm run migrate:schema
```

### Run Phase 1 only (safe optimizations)
```bash
npm run migrate:schema:phase1
```

### Run Phase 2 only (schema fixes)
```bash
npm run migrate:schema:phase2
```

### Dry run to preview changes
```bash
npm run migrate:schema:dry-run
```

### Show database statistics
```bash
npm run migrate:schema:stats
```

### Rollback Phase 1
```bash
npm run migrate:schema:rollback --phase="Phase 1"
```

### Test migration fixes
```bash
npm run migrate:schema:test
```

## Verification Results

### Before Migration
- ❌ Missing `idx_memories_user_type` index
- ❌ Missing `idx_memories_user_importance` index
- ✅ `api_key_hash` column exists (already migrated)
- ✅ No `learned_patterns` table

### After Migration (Expected)
- ✅ `idx_memories_user_type` created
- ✅ `idx_memories_user_importance` created
- ✅ All redundant indexes removed
- ✅ Optimized composite indexes in place
- ✅ Schema matches code expectations

## Code Quality

### LOC Impact
- **Net lines added:** ~50 lines (column check logic + new migration step)
- **Complexity reduced:** Simpler migration steps, better separation of concerns
- **Maintainability improved:** Clear error handling, idempotent operations

### TypeScript Compliance
- ✅ Strict mode enabled
- ✅ No `any` types
- ✅ Proper type inference
- ✅ All imports resolved

## Success Criteria

- [x] ALTER TABLE syntax error fixed
- [x] Column existence check implemented
- [x] Two missing composite indexes added to migration
- [x] Script compiles without errors
- [x] Dry-run shows all steps correctly
- [x] Migration logic handles edge cases (column already exists, index already exists)
- [x] Idempotency ensured
- [x] Clear error messages
- [x] Verification script updated
- [x] Documentation complete

## Next Steps

1. **Run Phase 1 migration** on production database:
   ```bash
   npm run migrate:schema:phase1
   ```

2. **Verify indexes created:**
   ```bash
   npm run migrate:schema:stats
   ```

3. **Monitor performance** after index optimization

4. **Run Phase 2 if needed** (only if schema inconsistencies exist):
   ```bash
   npm run migrate:schema:phase2
   ```

## Rollback Plan

If issues arise:

1. **Rollback Phase 2:**
   ```bash
   npm run migrate:schema:rollback --phase="Phase 2"
   ```

2. **Rollback Phase 1:**
   ```bash
   npm run migrate:schema:rollback --phase="Phase 1"
   ```

3. **Restore from backup** if needed:
   ```bash
   turso db shell <database-name> ".restore backup.db"
   ```

---

**Migration script:** `/Users/masa/Projects/managed/mcp-memory-ts/scripts/migrate-schema-optimization.ts`
**Test script:** `/Users/masa/Projects/managed/mcp-memory-ts/scripts/test-migration-fixes.ts`
**Date:** 2025-10-02
