PostgreSQL EXPLAIN ANALYZE & Composite Index Optimization Skill

Diagnose slow SQL queries using `EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON)`, eliminate sequential scans, design covering B-Tree/GIN indexes, and tune connect

---
name: postgres-query-tuning
description: Diagnose slow SQL queries using `EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON)`, eliminate sequential scans, design covering B-Tree/GIN indexes, and tune connection pools. Use when working with PostgreSQL, EXPLAIN ANALYZE, Indexing, pg_stat_statements.
triggers:
  - postgres query tuning
  - postgresql
  - explain analyze
---

# PostgreSQL EXPLAIN ANALYZE & Composite Index Optimization Skill

## 1. When to Use This Skill
Load `skill-postgres-query-tuning` whenever an engineering or operations task involves **PostgreSQL, EXPLAIN ANALYZE, Indexing, pg_stat_statements**. Specifically:
- Diagnose slow SQL queries using `EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON)`, eliminate sequential scans, design covering B-Tree/GIN indexes, and tune connection pools.
- Designing, reviewing, or debugging production configurations without guesswork or deprecated flags.
- Running deterministic pre-flight and post-execution verification checks before reporting completion.

## 2. Prerequisites & Required Environment
- **Target Stack:** PostgreSQL, EXPLAIN ANALYZE, Indexing, pg_stat_statements
- **Permissions:** Read-only inspection by default; ask for explicit confirmation before executing destructive mutations or production deployments.
- **Reference Repository:** `https://github.com/modelcontextprotocol/servers`

## 3. Step-by-Step Execution Playbook
1. **Context & Configuration Discovery:**
   Inspect existing project manifests (`package.json`, `wrangler.jsonc`, schema files, or environment declarations) before proposing changes. Never overwrite existing bindings or credentials blindly.
2. **Deterministic Implementation:**
   Apply the canonical patterns for **PostgreSQL**:
   - Enforce strict schema/type validation at every external boundary.
   - Include explicit error handling, structured logging, and idempotency keys on all mutating calls.
   - Keep secrets in environment variables or secret stores—never hardcode tokens in source files.
3. **Verification & Regression Gate:**
   Run the verification commands below and inspect both exit codes and output payloads before marking the task complete.

## 4. Reference Commands & CLI Workflow
```bash
psql $DATABASE_URL -c 'EXPLAIN (ANALYZE, BUFFERS) SELECT ...'
```

## 5. Edge Cases & Anti-Hallucination Guardrails
- **Zero Unverified Claims:** Never claim a deployment, migration, or API call succeeded without inspecting the command output or HTTP status code.
- **Rollback Readiness:** Always record the previous state or migration version so changes can be reverted cleanly if downstream health checks fail.

Synthesized Engineering Blueprint & Setup Guide