Postgres Best Practices

---
name: supabase-postgres-best-practices
description: Postgres performance optimization and best practices from Supabase. Use this skill when writing, reviewing, or optimizing Postgres queries, schema designs, or database configurations.
license: MIT
metadata:
  author: supabase
  version: "1.1.0"
  organization: Supabase
  date: January 2026
  abstract: Comprehensive Postgres performance optimization guide for developers using Supabase and Postgres. Contains performance rules across 8 categories, prioritized by impact from critical (query performance, connection management) to incremental (advanced features). Each rule includes detailed explanations, incorrect vs. correct SQL examples, query plan analysis, and specific performance metrics to guide automated optimization and code generation.
---

# Supabase Postgres Best Practices

Comprehensive performance optimization guide for Postgres, maintained by Supabase. Contains rules across 8 categories, prioritized by impact to guide automated query optimization and schema design.

## When to Apply

Reference these guidelines when:
- Writing SQL queries or designing schemas
- Implementing indexes or query optimization
- Reviewing database performance issues
- Configuring connection pooling or scaling
- Optimizing for Postgres-specific features
- Working with Row-Level Security (RLS)

## Rule Categories by Priority

| Priority | Category | Impact | Prefix |
|----------|----------|--------|--------|
| 1 | Query Performance | CRITICAL | `query-` |
| 2 | Connection Management | CRITICAL | `conn-` |
| 3 | Security & RLS | CRITICAL | `security-` |
| 4 | Schema Design | HIGH | `schema-` |
| 5 | Concurrency & Locking | MEDIUM-HIGH | `lock-` |
| 6 | Data Access Patterns | MEDIUM | `data-` |
| 7 | Monitoring & Diagnostics | LOW-MEDIUM | `monitor-` |
| 8 | Advanced Features | LOW | `advanced-` |

## How to Use

Read individual rule files for detailed explanations and SQL examples:

```
references/query-missing-indexes.md
references/schema-partial-indexes.md
references/_sections.md
```

Each rule file contains:
- Brief explanation of why it matters
- Incorrect SQL example with explanation
- Correct SQL example with explanation
- Optional EXPLAIN output or metrics
- Additional context and references
- Supabase-specific notes (when applicable)

## References

- https://www.postgresql.org/docs/current/
- https://supabase.com/docs
- https://wiki.postgresql.org/wiki/Performance_Optimization
- https://supabase.com/docs/guides/database/overview
- https://supabase.com/docs/guides/auth/row-level-security


---

## Companion Files

The following reference files are included for convenience:

### references/query-missing-indexes.md

---
title: Add Indexes on WHERE and JOIN Columns
impact: CRITICAL
impactDescription: 100-1000x faster queries on large tables
tags: indexes, performance, sequential-scan, query-optimization
---

## Add Indexes on WHERE and JOIN Columns

Queries filtering or joining on unindexed columns cause full table scans, which become exponentially slower as tables grow.

**Incorrect (sequential scan on large table):**

```sql
-- No index on customer_id causes full table scan
select * from orders where customer_id = 123;

-- EXPLAIN shows: Seq Scan on orders (cost=0.00..25000.00 rows=100 width=85)
```

**Correct (index scan):**

```sql
-- Create index on frequently filtered column
create index orders_customer_id_idx on orders (customer_id);

select * from orders where customer_id = 123;

-- EXPLAIN shows: Index Scan using orders_customer_id_idx (cost=0.42..8.44 rows=100 width=85)
```

For JOIN columns, always index the foreign key side:

```sql
-- Index the referencing column
create index orders_customer_id_idx on orders (customer_id);

select c.name, o.total
from customers c
join orders o on o.customer_id = c.id;
```

Reference: [Query Optimization](https://supabase.com/docs/guides/database/query-optimization)

### references/_sections.md

# Section Definitions

This file defines the rule categories for Postgres best practices. Rules are automatically assigned to sections based on their filename prefix.

Take the examples below as pure demonstrative. Replace each section with the actual rule categories for Postgres best practices.

---

## 1. Query Performance (query)
**Impact:** CRITICAL
**Description:** Slow queries, missing indexes, inefficient query plans. The most common source of Postgres performance issues.

## 2. Connection Management (conn)
**Impact:** CRITICAL
**Description:** Connection pooling, limits, and serverless strategies. Critical for applications with high concurrency or serverless deployments.

## 3. Security & RLS (security)
**Impact:** CRITICAL
**Description:** Row-Level Security policies, privilege management, and authentication patterns.

## 4. Schema Design (schema)
**Impact:** HIGH
**Description:** Table design, index strategies, partitioning, and data type selection. Foundation for long-term performance.

## 5. Concurrency & Locking (lock)
**Impact:** MEDIUM-HIGH
**Description:** Transaction management, isolation levels, deadlock prevention, and lock contention patterns.

## 6. Data Access Patterns (data)
**Impact:** MEDIUM
**Description:** N+1 query elimination, batch operations, cursor-based pagination, and efficient data fetching.

## 7. Monitoring & Diagnostics (monitor)
**Impact:** LOW-MEDIUM
**Description:** Using pg_stat_statements, EXPLAIN ANALYZE, metrics collection, and performance diagnostics.

## 8. Advanced Features (advanced)
**Impact:** LOW
**Description:** Full-text search, JSONB optimization, PostGIS, extensions, and advanced Postgres features.