---
name: db-anti-patterns
description: "Detection rules and grep patterns for database performance anti-patterns. Use when scanning codebase for N+1 queries, sequential queries, or connection pool issues."
---

# Database Anti-Patterns Detection

Detection rules and grep patterns for identifying database performance anti-patterns in code.

## When to Use This Skill

- Scanning codebase for performance issues
- Code review for database patterns
- Used by `db-performance-agent` for automated detection

## Anti-Pattern Categories

### 1. N+1 Query Patterns (CRITICAL)

Queries executed inside loops - causes O(n) database calls.

**Detection Patterns:**

```typescript
// Pattern 1: await inside for loop
for (const item of items) {
  await supabase.from('table')...  // N+1!
}

// Pattern 2: await inside forEach
items.forEach(async (item) => {
  await supabase.from('table')...  // N+1!
});

// Pattern 3: await inside map
await Promise.all(items.map(async (item) => {
  await supabase.from('table')...  // N+1 even with Promise.all!
}));

// Pattern 4: count queries in loop
for (const item of items) {
  const { count } = await supabase.from('x').select('id', { count: 'exact' })...
}
```

**Grep Patterns:**

```bash
# For loops with await supabase
grep -Pzo 'for\s*\([^)]+\)\s*\{[^}]*await[^}]*\.from\(' --include="*.ts"

# forEach with async
grep -n 'forEach\s*\(\s*async' --include="*.ts"

# map with nested await from()
grep -n '\.map\s*\(\s*async.*await.*\.from\(' --include="*.ts"
```

**Severity:** CRITICAL
**Impact:** 50-500+ queries per request
**Auto-fixable:** Yes - batch fetch + Map lookup

---

### 2. Sequential Independent Queries (HIGH)

Multiple await statements that could run in parallel.

**Detection Pattern:**

```typescript
// Sequential (BAD)
const a = await supabase.from('table_a').select()...;
const b = await supabase.from('table_b').select()...;
const c = await supabase.from('table_c').select()...;

// Should be parallel (GOOD)
const [a, b, c] = await Promise.all([
  supabase.from('table_a').select()...,
  supabase.from('table_b').select()...,
  supabase.from('table_c').select()...,
]);
```

**Detection Heuristic:**

Look for 2+ consecutive lines matching:
- `const/let X = await supabase.from(...)`
- With no data dependency between them

**Severity:** HIGH
**Impact:** 2-5x latency increase
**Auto-fixable:** Yes - wrap in Promise.all()

---

### 3. Unbounded Data Fetches (MEDIUM)

Queries without `.limit()` on tables that can grow large.

**Large Tables to Check:**

```typescript
const LARGE_TABLES = [
  'events',
  'cast_assignments',
  'invoices',
  'invoice_line_items',
  'notifications',
  'notification_deliveries',
  'airtable_sync_changes',
  'audit_logs',
  'feedback_requests',
  'reimbursements',
  'reimbursement_line_items',
];
```

**Detection Pattern:**

```typescript
// Missing limit (BAD for large tables)
await supabase.from('events').select('*')

// Should have limit or be filtered (GOOD)
await supabase.from('events').select('*').limit(100)
await supabase.from('events').select('*').eq('user_id', userId)
```

**Grep Pattern:**

```bash
# Selects on large tables without limit
grep -n "\.from\(['\"]events['\"]\)" --include="*.ts" | grep -v "\.limit\|\.eq\|\.in\|\.single"
```

**Severity:** MEDIUM
**Impact:** Memory exhaustion, slow queries
**Auto-fixable:** Partial - add .limit(), may need review

---

### 4. Individual Insert/Update in Loops (HIGH)

Single-row operations that should be batched.

**Detection Pattern:**

```typescript
// Individual inserts (BAD)
for (const item of items) {
  await supabase.from('table').insert({ ...item });
}

// Individual updates (BAD)
for (const id of ids) {
  await supabase.from('table').update({ status: 'done' }).eq('id', id);
}

// Batch operations (GOOD)
await supabase.from('table').insert(items);
await supabase.from('table').update({ status: 'done' }).in('id', ids);
```

**Grep Pattern:**

```bash
# Insert in loop
grep -Pzo 'for\s*\([^)]+\)\s*\{[^}]*\.insert\(' --include="*.ts"

# Update in loop
grep -Pzo 'for\s*\([^)]+\)\s*\{[^}]*\.update\(' --include="*.ts"
```

**Severity:** HIGH
**Impact:** N database round-trips
**Auto-fixable:** Yes - batch operations

---

### 5. Count Queries Instead of Aggregation (MEDIUM)

Using multiple COUNT queries instead of fetching once and aggregating.

**Detection Pattern:**

```typescript
// Multiple count queries (BAD)
const { count: countA } = await supabase.from('x').select('id', { count: 'exact' }).eq('status', 'a');
const { count: countB } = await supabase.from('x').select('id', { count: 'exact' }).eq('status', 'b');
const { count: countC } = await supabase.from('x').select('id', { count: 'exact' }).eq('status', 'c');

// Single fetch + aggregate (GOOD)
const { data } = await supabase.from('x').select('status').in('status', ['a', 'b', 'c']);
const counts = { a: 0, b: 0, c: 0 };
for (const item of data) counts[item.status]++;
```

**Grep Pattern:**

```bash
# Multiple count queries (look for pattern of consecutive count selects)
grep -n "count: 'exact'" --include="*.ts"
```

**Severity:** MEDIUM
**Impact:** 2-10x more queries than necessary
**Auto-fixable:** Yes - single query + in-memory aggregation

---

### 6. Missing Promise.all for Related Lookups (MEDIUM)

Fetching the same related entity type multiple times sequentially.

**Detection Pattern:**

```typescript
// Sequential related lookups (BAD)
const user1 = await getUser(id1);
const user2 = await getUser(id2);
const user3 = await getUser(id3);

// Batch lookup (GOOD)
const users = await getUsers([id1, id2, id3]);
```

**Severity:** MEDIUM
**Impact:** Increased latency
**Auto-fixable:** Sometimes - depends on function signature

---

## Quick Reference: Detection Commands

```bash
# Find all N+1 patterns (for loops with await from)
grep -rn "for.*{" apps/web --include="*.ts" | xargs -I {} sh -c 'grep -l "await.*\.from\(" {}'

# Find sequential queries (consecutive await from lines)
grep -n "await.*\.from\(" apps/web --include="*.ts" | sort | uniq -c | sort -rn

# Find unbounded selects on large tables
for table in events cast_assignments invoices notifications; do
  grep -rn "\.from(['\"]$table['\"])" apps/web --include="*.ts" | grep -v "\.limit\|\.single\|\.eq\|\.in"
done

# Find insert/update in loops
grep -rn "for\s*(" apps/web --include="*.ts" -A 5 | grep -E "\.(insert|update)\("

# Find multiple count queries in same file
grep -l "count: 'exact'" apps/web --include="*.ts" -r | xargs -I {} grep -c "count: 'exact'" {} | grep -v ":1$"
```

## Severity Levels

| Severity | Impact | Fix Priority |
|----------|--------|--------------|
| CRITICAL | 10x+ queries, pool exhaustion risk | Immediate |
| HIGH | 3-10x queries/latency | Same sprint |
| MEDIUM | 2-3x queries/latency | Next sprint |
| LOW | Minor inefficiency | Backlog |

## Files Commonly Affected

High-risk file patterns to prioritize scanning:

1. **Cron jobs**: `app/api/cron/*/route.ts`
2. **Services with batch ops**: `**/services/*.service.ts`
3. **Admin list pages**: `app/admin/**/actions.ts`
4. **Report generators**: `**/reporting*.ts`

## Related Skills

- `db-performance-patterns` - Correct patterns and fixes
- `db-performance-agent` - Automated scanning and fixing


---
Source attribution: JaveedIshaq
Original project: https://github.com/JaveedIshaq/ai-workflow-orchestrator/blob/6b54ecbdcacca21d769e634f21ec2674f28b6cc9/skills/ballee/db-anti-patterns/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Dave AI.

## Upstream license notice

MIT License

Copyright (c) 2025 Antoine Schaller

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Dave AI resource metadata

Creator / publisher: JaveedIshaq
Original project: https://github.com/JaveedIshaq/ai-workflow-orchestrator/blob/6b54ecbdcacca21d769e634f21ec2674f28b6cc9/skills/ballee/db-anti-patterns/SKILL.md
Attribution basis: Recovered original package and original project license at a pinned revision

Fields of work: Development & Engineering
Roles: Backend Developer, Data Engineer, Database Administrator, QA / Test Engineer
Specialties: Database
Tools: Supabase
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: b76286d02ab9e4f14668793381431165674b53ae3aa0b64b234b526ff0751356
Metadata reviewed: 2026-10-27
This metadata supersedes earlier Dave AI catalog attribution. Original instruction and supporting files are preserved.