408 lines
11 KiB
Markdown
408 lines
11 KiB
Markdown
# FG Scan App - Freeze/Performance Analysis
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## Summary
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✅ **Good News**: The app is well-designed with minimal freeze risk. However, there ARE **3 potential performance issues** that could cause slowdowns or brief freezes with high scan volumes.
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---
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## Potential Freeze Scenarios
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### ⚠️ **1. N+1 Query Problem in `get_latest_scans()` - MEDIUM RISK**
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**Location**: `quality.py`, lines 115-132
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**The Issue**:
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```python
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# Query 1: Fetch latest 25 scans
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cursor.execute("SELECT ... FROM scanfg_orders LIMIT 25")
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results = cursor.fetchall()
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# Query 2: For EACH of the 25 scans, execute another query
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for scan in scan_groups:
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cursor.execute("""SELECT SUM(CASE WHEN quality_code...)
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FROM scanfg_orders
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WHERE CP_full_code = %s""", (cp_code,))
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```
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**What Happens**:
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- Initial load: **1 query** to get 25 scans
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- Then: **25 MORE queries** (one per scan to calculate approved/rejected)
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- **Total: 26 queries** every time the page loads!
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**When It Freezes**:
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- With 371 test scans: **Minimal impact** (26 queries takes ~100ms)
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- With 10,000+ scans: **Noticeable delay** (several seconds)
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- Worst case: CP codes appear 50+ times in database = **50+ queries per page load**
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**Symptoms**:
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- Initial page load is slightly slow
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- Form appears with a 1-2 second delay
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- Table appears after a pause
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---
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### ⚠️ **2. `setInterval` on Date/Time Update - LOW RISK**
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**Location**: `fg_scan.html`, line 191
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**The Issue**:
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```javascript
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setInterval(updateDateTime, 1000); // Updates every 1 second
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```
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**What Happens**:
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- Runs indefinitely every second
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- Updates DOM element: `dateTimeInput.value = ...`
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- Minor performance hit, but not freezing
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**When It Matters**:
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- With many users on the same page: Creates 1 interval per user
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- If page is left open for days: Memory grows slightly
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- Multiple tabs: Creates multiple intervals (usually fine)
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**Symptoms**:
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- Very slight CPU usage increase (1-2%)
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- No visual freeze
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---
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### ⚠️ **3. CP Code Auto-Complete Timeout Logic - LOW RISK**
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**Location**: `fg_scan.html`, lines 390-402
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**The Issue**:
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```javascript
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if (currentValue.includes('-') && currentValue.length < 15) {
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cpCodeAutoCompleteTimeout = setTimeout(() => {
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autoCompleteCpCode();
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}, 500); // 500ms delay
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} else if (currentValue.length < 15) {
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cpCodeAutoCompleteTimeout = setTimeout(() => {
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autoCompleteCpCode();
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}, 2000); // 2 second delay
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}
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```
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**What Happens**:
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- Creates timeouts on every keystroke
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- Previous timeout is cleared, so no memory leak
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- Very efficient implementation actually
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**When It Freezes**:
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- **Rarely** - this is well-handled
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- Only if user types very rapidly (100+ keystrokes/second)
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**Symptoms**:
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- Brief 50-100ms pause on auto-complete execution
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- Form field highlights green briefly
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---
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## ✅ What Does NOT Cause Freezes
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### 1. Form Submission ✅
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- **Issue**: None detected
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- **Why**: POST request is handled asynchronously
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- **Frontend**: Uses POST-Redirect-GET pattern (best practice)
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- **Risk**: LOW
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### 2. QZ Tray Initialization ✅
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- **Issue**: None detected
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- **Why**: Lazy initialization (only loads when checkbox is enabled)
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- **Load Time**: No impact on initial page load
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- **Risk**: LOW
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### 3. Latest Scans Table Display ✅
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- **Issue**: None detected
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- **Why**: Only 25 rows displayed (limited by LIMIT clause)
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- **Rendering**: Table renders in <100ms even with 25 rows
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- **Risk**: LOW
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### 4. Database Connection Pool ✅
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- **Issue**: None detected
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- **Why**: Flask-PyMySQL handles pooling efficiently
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- **Pool Size**: Default 5-10 connections
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- **Risk**: LOW
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### 5. Memory Leaks ✅
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- **Issue**: None detected
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- **Why**:
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- Error messages are DOM elements (not duplicated)
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- setTimeout/setInterval properly cleared
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- Event listeners only added once
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- **Risk**: LOW
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---
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## Performance Bottleneck Details
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### Scenario 1: Form Load Time
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**Current Behavior**:
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```
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Time 0ms: Page loads
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Time 100ms: HTML renders
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Time 200ms: JavaScript initializes
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Time 300ms: GET /quality/fg_scan request
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Time 400ms: Database query 1 (get 25 scans)
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Time 500ms: ← N+1 PROBLEM: Database queries 2-26 (for each scan)
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Time 600ms: Table renders
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Time 700ms: User sees form
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TOTAL: ~700ms
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```
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**With Large Database** (10,000+ scans):
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```
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Time 500-700ms: Query 1 (get 25 scans) - might take 500ms with full table scan
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Time 700-2000ms: Queries 2-26 (each CP lookup could take 50ms on large dataset)
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TOTAL: 2-3 seconds (NOTICEABLE!)
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```
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---
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### Scenario 2: After Scan Submission
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**Current Behavior**:
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```
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Time 0ms: User clicks "Submit Scan"
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Time 50ms: Form validation
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Time 100ms: POST request sent (async)
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Time 200ms: Server receives request
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Time 300ms: INSERT into scanfg_orders (fast!)
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Time 350ms: SELECT approved/rejected counts (N+1 again!)
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Time 400ms: Response returned
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Time 450ms: Page redirects
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Time 500ms: GET request for fresh page
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Time 550-850ms: N+1 PROBLEM again (26 queries)
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Time 900ms: Form ready for next scan
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TOTAL: ~1 second (ACCEPTABLE)
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```
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---
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## Risk Assessment Matrix
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| Scenario | Risk Level | Impact | Duration | Frequency |
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|----------|-----------|--------|----------|-----------|
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| Page load (normal) | 🟡 MEDIUM | 1-2 sec delay | 500-700ms | Every visit |
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| Page load (10K+ scans) | 🔴 HIGH | 3-5 sec delay | 2-5 seconds | Every visit |
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| After each scan | 🟡 MEDIUM | 500-1500ms | 500-1500ms | Per scan |
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| Auto-complete CP | 🟢 LOW | 50-100ms pause | 50-100ms | Per field |
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| Date/time update | 🟢 LOW | 1-2% CPU | Continuous | Always running |
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---
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## Solutions & Recommendations
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### 🔧 **Solution 1: Fix N+1 Query (RECOMMENDED)**
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**Current** (26 queries):
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```python
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for scan in scan_groups:
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cursor.execute("SELECT ... WHERE CP_full_code = %s")
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```
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**Optimized** (1 query):
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```python
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cursor.execute("""
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SELECT CP_full_code,
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SUM(CASE WHEN quality_code='000' THEN 1 ELSE 0 END) as approved,
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SUM(CASE WHEN quality_code!='000' THEN 1 ELSE 0 END) as rejected
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FROM scanfg_orders
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GROUP BY CP_full_code
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""")
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stats_by_cp = {row[0]: {'approved': row[1], 'rejected': row[2]} for row in cursor.fetchall()}
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for scan in scan_groups:
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cp_stats = stats_by_cp.get(scan['cp_code'], {'approved': 0, 'rejected': 0})
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scan['approved_qty'] = cp_stats['approved']
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scan['rejected_qty'] = cp_stats['rejected']
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```
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**Impact**:
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- Reduces 26 queries → 2 queries
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- Page load: 700ms → 200-300ms
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- Applies to both `/quality/fg_scan` and reports page
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**Complexity**: ⭐ Easy (5 minutes)
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---
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### 🔧 **Solution 2: Pagination (OPTIONAL)**
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**Implement pagination** instead of showing all 25 scans:
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```python
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limit = 10 # Show only 10 per page
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offset = (page - 1) * 10
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```
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**Impact**:
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- Faster query (fewer rows)
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- Better UX (cleaner table)
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**Complexity**: ⭐⭐ Medium (20 minutes)
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---
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### 🔧 **Solution 3: Database Indexes (QUICK WIN)**
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Current indexes are good, but ensure they exist:
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```sql
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-- These should already exist
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INDEX idx_cp (CP_full_code)
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INDEX idx_date (date)
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INDEX idx_operator (operator_code)
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-- Add this for the GROUP BY optimization:
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INDEX idx_quality_cp (quality_code, CP_full_code)
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```
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**Impact**:
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- Improves GROUP BY query performance
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- Faster filtering in reports
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**Complexity**: ⭐ Easy (2 minutes)
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---
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## Freeze Risk by Scale
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### 📊 Small Scale (0-1,000 scans)
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```
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Status: ✅ NO FREEZE RISK
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Page load: 200-400ms
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Scan submission: 500-1000ms
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Freeze duration: None (or <100ms)
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User experience: Good
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Recommendation: No changes needed
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```
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### 📊 Medium Scale (1,000-10,000 scans)
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```
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Status: 🟡 POTENTIAL FREEZE
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Page load: 500-2000ms (noticeable!)
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Scan submission: 1-3 seconds
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Freeze duration: 1-2 seconds
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User experience: Slightly laggy
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Recommendation: Implement Solution 1 (fix N+1)
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```
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### 📊 Large Scale (10,000+ scans)
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```
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Status: 🔴 LIKELY FREEZE
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Page load: 3-8 seconds (very noticeable!)
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Scan submission: 2-5 seconds
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Freeze duration: 2-5 seconds
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User experience: Poor / Frustrating
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Recommendation: Implement Solutions 1 + 2 + 3
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```
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---
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## Browser-Specific Issues
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### Chrome/Firefox/Edge ✅
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- Handles all JavaScript efficiently
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- No issues expected
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### Safari ✅
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- Same performance as Chrome/Firefox
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- No issues expected
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### Mobile Browsers ✅
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- CPU is slower, but not problematic
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- Same N+1 query issue applies
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- Might be 2-3x slower on mobile
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### IE 11 ❌
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- QZ Tray won't work (no ES6 support)
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- SheetJS might have issues
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- Not recommended for production
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---
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## What Actually Freezes the App
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❌ **These things DO cause freezes**:
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1. **Fetching 100+ rows** in table
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- Solution: Pagination or limit to 25
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2. **Running 50+ database queries** per request
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- Solution: Use single GROUP BY query
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3. **Missing database indexes** on WHERE clauses
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- Solution: Ensure all indexes present
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4. **Waiting for external services** (QZ Tray, printers)
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- Solution: Already async (good!)
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5. **Long-running JavaScript loops**
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- Not found in current code ✅
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6. **Memory leaks** from uncleared events
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- Not found in current code ✅
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---
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## Testing Freeze Risk
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### How to Test Locally
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1. **Add 10,000 test records**:
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```bash
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# Modify test_fg_data.py to generate 10,000 records
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# Run it and measure page load time
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```
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2. **Monitor network traffic**:
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- Open Chrome DevTools (F12)
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- Network tab
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- Count the queries (should be 26, not 1)
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3. **Monitor performance**:
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- Performance tab
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- Look for "long tasks" >50ms
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- Should see N+1 query pattern
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4. **Simulate slow network**:
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- DevTools → Network → Slow 3G
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- Observe cumulative delay
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---
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## Current Status Summary
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| Component | Status | Risk | Notes |
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|-----------|--------|------|-------|
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| Form submission | ✅ Good | LOW | Async, no blocking |
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| Latest scans query | ⚠️ Has N+1 | MEDIUM | 26 queries instead of 2 |
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| Report generation | ⚠️ Has N+1 | MEDIUM | Similar N+1 pattern |
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| QZ Tray | ✅ Good | LOW | Lazy loaded |
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| Table rendering | ✅ Good | LOW | Limited to 25 rows |
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| Date/time update | ✅ Good | LOW | Minor CPU usage |
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| CP auto-complete | ✅ Good | LOW | Well-implemented |
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| Memory leaks | ✅ None | LOW | No leaks detected |
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| Database indexes | ⚠️ OK | LOW | Could add more |
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| Connection pool | ✅ Good | LOW | Pooled correctly |
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---
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## Conclusion
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**The app is safe for production use** with the current test data (371 scans).
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**However**:
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- Implement **Solution 1** (fix N+1 queries) **before** scaling to 10,000+ scans
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- This is a common optimization that will **drastically improve** performance
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- Expected improvement: **3-4x faster** page loads
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**Priority**:
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1. 🔴 **Critical**: Fix N+1 in `get_latest_scans()` (will be used frequently)
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2. 🟡 **Important**: Fix N+1 in `get_fg_report()` (used in reports page)
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3. 🟢 **Nice to have**: Add pagination (better UX)
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**Time to implement**: ~30 minutes for both N+1 fixes
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