# Clickhouse Best Practices

> MUST USE when reviewing ClickHouse schemas, queries, or configurations. Contains 31 rules that MUST be checked before providing recommendations. Always read relevant rule files and cite specific rules in responses.

Fuente: https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-best-practices
Markdown: https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-best-practices.md

Repositorio: https://github.com/ClickHouse/agent-skills
Autor: ClickHouse
Licencia: Apache-2.0
Actualizado: hace 3 meses
Coste de contexto: 54 tok instalada, 2.6k tok al activarse, 35.4k tok con todos los archivos del bundle
Bundle: 37 archivos, 138 KB
Permisos que pide: ninguno declarado

## Instalación

Un skill son archivos markdown: los mismos archivos valen para cualquier agente y lo único que cambia es el directorio de destino, es decir la bandera `--agent`. Añade `-g` para instalarlo en todos los proyectos de la máquina.

```bash
# Claude Code
npx -y skills add ClickHouse/agent-skills --skill clickhouse-best-practices --agent claude-code
# Cursor
npx -y skills add ClickHouse/agent-skills --skill clickhouse-best-practices --agent cursor
# Codex
npx -y skills add ClickHouse/agent-skills --skill clickhouse-best-practices --agent codex
# Gemini CLI
npx -y skills add ClickHouse/agent-skills --skill clickhouse-best-practices --agent gemini
# Windsurf
npx -y skills add ClickHouse/agent-skills --skill clickhouse-best-practices --agent windsurf
# Cline
npx -y skills add ClickHouse/agent-skills --skill clickhouse-best-practices --agent cline
```

## Archivos

- AGENTS.md — 62 KB
- README.md — 2 KB
- SKILL.md — 10 KB
- metadata.json — 643 B
- rules/_sections.md — 2 KB
- rules/_template.md — 624 B
- rules/agent-connect-mcp.md — 4 KB
- rules/agent-discovery-schema.md — 6 KB
- rules/agent-query-safety.md — 5 KB
- rules/insert-async-small-batches.md — 2 KB
- rules/insert-batch-size.md — 1 KB
- rules/insert-format-native.md — 933 B
- rules/insert-mutation-avoid-delete.md — 2 KB
- rules/insert-mutation-avoid-update.md — 2 KB
- rules/insert-optimize-avoid-final.md — 2 KB
- rules/query-index-skipping-indices.md — 2 KB
- rules/query-join-choose-algorithm.md — 2 KB
- rules/query-join-consider-alternatives.md — 2 KB
- rules/query-join-filter-before.md — 1 KB
- rules/query-join-null-handling.md — 1 KB
- rules/query-join-use-any.md — 1 KB
- rules/query-mv-incremental.md — 2 KB
- rules/query-mv-refreshable.md — 2 KB
- rules/schema-json-when-to-use.md — 2 KB
- rules/schema-partition-lifecycle.md — 2 KB
- rules/schema-partition-low-cardinality.md — 2 KB
- rules/schema-partition-query-tradeoffs.md — 1 KB
- rules/schema-partition-start-without.md — 1 KB
- rules/schema-pk-cardinality-order.md — 2 KB
- rules/schema-pk-filter-on-orderby.md — 2 KB
- rules/schema-pk-plan-before-creation.md — 2 KB
- rules/schema-pk-prioritize-filters.md — 1 KB
- rules/schema-types-avoid-nullable.md — 2 KB
- rules/schema-types-enum.md — 2 KB
- rules/schema-types-lowcardinality.md — 2 KB
- rules/schema-types-minimize-bitwidth.md — 1 KB
- rules/schema-types-native-types.md — 2 KB

## SKILL.md

Reproducido tal cual desde ClickHouse/agent-skills bajo Apache-2.0. Esta sección es el documento original y está en inglés.

# ClickHouse Best Practices

Comprehensive guidance for ClickHouse covering schema design, query optimization, data ingestion, and AI agent connectivity. Contains 31 rules across 4 main categories (schema, query, insert, agent), prioritized by impact.

> **Official docs:** [ClickHouse Best Practices](https://clickhouse.com/docs/best-practices)

## IMPORTANT: How to Apply This Skill

**Before answering ClickHouse questions, follow this priority order:**

1. **Check for applicable rules** in the `rules/` directory
2. **If rules exist:** Apply them and cite them in your response using "Per `rule-name`..."
3. **If no rule exists:** Use the LLM's ClickHouse knowledge or search documentation
4. **If uncertain:** Use web search for current best practices
5. **Always cite your source:** rule name, "general ClickHouse guidance", or URL

**Why rules take priority:** ClickHouse has specific behaviors (columnar storage, sparse indexes, merge tree mechanics) where general database intuition can be misleading. The rules encode validated, ClickHouse-specific guidance.

---

## Agent Connectivity & Query Workflow

Before querying ClickHouse, agents must establish a connection and follow the discovery workflow:

1. `rules/agent-connect-mcp.md` - Connection setup (MCP + CLI), credential discovery, output format selection
2. `rules/agent-discovery-schema.md` - **CRITICAL**: 7-step schema discovery workflow
3. `rules/agent-query-safety.md` - **CRITICAL**: LIMIT, timeouts, progressive exploration

**Every agent session should follow this sequence:**

1. **Connect** — establish connection via MCP or CLI (see `agent-connect-mcp`)
2. **Discover** — databases → tables → columns + comments → sort keys → skip indexes → sample → EXPLAIN
3. **Plan** — use sort key and skip index knowledge to write efficient WHERE clauses
4. **Execute** — run queries with LIMIT and timeouts
5. **Recover** — on timeout/memory errors, narrow filters and retry (see `agent-query-safety`)

### Subagent architecture notes

If your system dispatches ClickHouse tasks to specialized subagents:
- **Schema discovery + query execution**: any model — the steps are procedural
- **EXPLAIN analysis + query optimization**: benefits from mid-tier reasoning
- **Schema design review against all 28 rules**: benefits from mid-tier reasoning

---

## Review Procedures

### For Schema Reviews (CREATE TABLE, ALTER TABLE)

**Read these rule files in order:**

1. `rules/schema-pk-plan-before-creation.md` - ORDER BY is immutable
2. `rules/schema-pk-cardinality-order.md` - Column ordering in keys
3. `rules/schema-pk-prioritize-filters.md` - Filter column inclusion
4. `rules/schema-types-native-types.md` - Proper type selection
5. `rules/schema-types-minimize-bitwidth.md` - Numeric type sizing
6. `rules/schema-types-lowcardinality.md` - LowCardinality usage
7. `rules/schema-types-avoid-nullable.md` - Nullable vs DEFAULT
8. `rules/schema-partition-low-cardinality.md` - Partition count limits
9. `rules/schema-partition-lifecycle.md` - Partitioning purpose

**Check for:**
- [ ] PRIMARY KEY / ORDER BY column order (low-to-high cardinality)
- [ ] Data types match actual data ranges
- [ ] LowCardinality applied to appropriate string columns
- [ ] Partition key cardinality bounded (100-1,000 values)
- [ ] ReplacingMergeTree has version column if used

### For Query Reviews (SELECT, JOIN, aggregations)

**Read these rule files:**

1. `rules/query-join-choose-algorithm.md` - Algorithm selection
2. `rules/query-join-filter-before.md` - Pre-join filtering
3. `rules/query-join-use-any.md` - ANY vs regular JOIN
4. `rules/query-index-skipping-indices.md` - Secondary index usage
5. `rules/schema-pk-filter-on-orderby.md` - Filter alignment with ORDER BY

**Check for:**
- [ ] Filters use ORDER BY prefix columns
- [ ] JOINs filter tables before joining (not after)
- [ ] Correct JOIN algorithm for table sizes
- [ ] Skipping indices for non-ORDER BY filter columns

### For Insert Strategy Reviews (data ingestion, updates, deletes)

**Read these rule files:**

1. `rules/insert-batch-size.md` - Batch sizing requirements
2. `rules/insert-mutation-avoid-update.md` - UPDATE alternatives
3. `rules/insert-mutation-avoid-delete.md` - DELETE alternatives
4. `rules/insert-async-small-batches.md` - Async insert usage
5. `rules/insert-optimize-avoid-final.md` - OPTIMIZE TABLE risks

**Check for:**
- [ ] Batch size 10K-100K rows per INSERT
- [ ] No ALTER TABLE UPDATE for frequent changes
- [ ] ReplacingMergeTree or CollapsingMergeTree for update patterns
- [ ] Async inserts enabled for high-frequency small batches

---

## Output Format

Structure your response as follows:

```
## Rules Checked
- `rule-name-1` - Compliant / Violation found
- `rule-name-2` - Compliant / Violation found
...

## Findings

### Violations
- **`rule-name`**: Description of the issue
  - Current: [what the code does]
  - Required: [what it should do]
  - Fix: [specific correction]

### Compliant
- `rule-name`: Brief note on why it's correct

## Recommendations
[Prioritized list of changes, citing rules]
```

---

## Rule Categories by Priority

| Priority | Category | Impact | Prefix | Rule Count |
|----------|----------|--------|--------|------------|
| 1 | Primary Key Selection | CRITICAL | `schema-pk-` | 4 |
| 2 | Data Type Selection | CRITICAL | `schema-types-` | 5 |
| 3 | JOIN Optimization | CRITICAL | `query-join-` | 5 |
| 4 | Insert Batching | CRITICAL | `insert-batch-` | 1 |
| 5 | Mutation Avoidance | CRITICAL | `insert-mutation-` | 2 |
| 6 | Partitioning Strategy | HIGH | `schema-partition-` | 4 |
| 7 | Skipping Indices | HIGH | `query-index-` | 1 |
| 8 | Materialized Views | HIGH | `query-mv-` | 2 |
| 9 | Async Inserts | HIGH | `insert-async-` | 2 |
| 10 | OPTIMIZE Avoidance | HIGH | `insert-optimize-` | 1 |
| 11 | JSON Usage | MEDIUM | `schema-json-` | 1 |
| 12 | Agent Schema Discovery | CRITICAL | `agent-discovery-` | 1 |
| 13 | Agent Query Safety | CRITICAL | `agent-query-` | 1 |
| 14 | Agent Connectivity + Formats | HIGH | `agent-connect-` | 1 |

---

## Quick Reference

### Schema Design - Primary Key (CRITICAL)

- `schema-pk-plan-before-creation` - Plan ORDER BY before table creation (immutable)
- `schema-pk-cardinality-order` - Order columns low-to-high cardinality
- `schema-pk-prioritize-filters` - Include frequently filtered columns
- `schema-pk-filter-on-orderby` - Query filters must use ORDER BY prefix

### Schema Design - Data Types (CRITICAL)

- `schema-types-native-types` - Use native types, not String for everything
- `schema-types-minimize-bitwidth` - Use smallest numeric type that fits
- `schema-types-lowcardinality` - LowCardinality for <10K unique strings
- `schema-types-enum` - Enum for finite value sets with validation
- `schema-types-avoid-nullable` - Avoid Nullable; use DEFAULT instead

### Schema Design - Partitioning (HIGH)

- `schema-partition-low-cardinality` - Keep partition count 100-1,000
- `schema-partition-lifecycle` - Use partitioning for data lifecycle, not queries
- `schema-partition-query-tradeoffs` - Understand partition pruning trade-offs
- `schema-partition-start-without` - Consider starting without partitioning

### Schema Design - JSON (MEDIUM)

- `schema-json-when-to-use` - JSON for dynamic schemas; typed columns for known

### Query Optimization - JOINs (CRITICAL)

- `query-join-choose-algorithm` - Select algorithm based on table sizes
- `query-join-use-any` - ANY JOIN when only one match needed
- `query-join-filter-before` - Filter tables before joining
- `query-join-consider-alternatives` - Dictionaries/denormalization vs JOIN
- `query-join-null-handling` - join_use_nulls=0 for default values

### Query Optimization - Indices (HIGH)

- `query-index-skipping-indices` - Skipping indices for non-ORDER BY filters

### Query Optimization - Materialized Views (HIGH)

- `query-mv-incremental` - Incremental MVs for real-time aggregations
- `query-mv-refreshable` - Refreshable MVs for complex joins

### Insert Strategy - Batching (CRITICAL)

- `insert-batch-size` - Batch 10K-100K rows per INSERT

### Insert Strategy - Async (HIGH)

- `insert-async-small-batches` - Async inserts for high-frequency small batches
- `insert-format-native` - Native format for best performance

### Insert Strategy - Mutations (CRITICAL)

- `insert-mutation-avoid-update` - ReplacingMergeTree instead of ALTER UPDATE
- `insert-mutation-avoid-delete` - Lightweight DELETE or DROP PARTITION

### Insert Strategy - Optimization (HIGH)

- `insert-optimize-avoid-final` - Let background merges work

### Agent Integration - Discovery (CRITICAL)

- `agent-discovery-schema` - Always discover schema before querying

### Agent Integration - Safety (CRITICAL)

- `agent-query-safety` - LIMIT, timeouts, progressive exploration

### Agent Integration - Connectivity + Formats (HIGH)

- `agent-connect-mcp` - MCP + CLI setup, credential discovery, output format selection

---

## When to Apply

This skill activates when you encounter:

- AI agent connecting to ClickHouse (MCP, CLI, HTTP)
- Agent workflow design for ClickHouse
- Schema discovery or exploration requests

- `CREATE TABLE` statements
- `ALTER TABLE` modifications
- `ORDER BY` or `PRIMARY KEY` discussions
- Data type selection questions
- Slow query troubleshooting
- JOIN optimization requests
- Data ingestion pipeline design
- Update/delete strategy questions
- ReplacingMergeTree or other specialized engine usage
- Partitioning strategy decisions

---

## Rule File Structure

Each rule file in `rules/` contains:

- **YAML frontmatter**: title, impact level, tags
- **Brief explanation**: Why this rule matters
- **Incorrect example**: Anti-pattern with explanation
- **Correct example**: Best practice with explanation
- **Additional context**: Trade-offs, when to apply, references

---

## Full Compiled Document

For the complete guide with all rules expanded inline: `AGENTS.md`

Use `AGENTS.md` when you need to check multiple rules quickly without reading individual files.

## Dónde encaja

- Categoría: [Bases de datos](https://skillsagentes.com/categorias/bases-de-datos.md) — Diseño de esquemas, migraciones y optimización de consultas.
- Creador: [ClickHouse](https://skillsagentes.com/creators/clickhouse.md) — 11 skills en el directorio
- [Todas las skills](https://skillsagentes.com/skills.md)
- [Ranking de instalaciones](https://skillsagentes.com/ranking.md)

## Otras skills del mismo repositorio

- [Clickhouse Js Node Rowbinary](https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-js-node-rowbinary.md): Generate TypeScript/JavaScript code that reads/decodes AND writes/encodes ClickHouse RowBinary streams for the ClickHouse HTTP server. Use this skill whenever a user wants to parse or produce `RowBinary`, `RowBinaryWithNames`, or `RowBinaryWithNamesAndTypes`. Node.js only, doesn't cover browsers.
- [Infra Clickhouse](https://skillsagentes.com/skills/clickhouse/agent-skills/infra-clickhouse.md): Sets up and manages ClickHouse using the clickhousectl CLI — installs and runs a local ClickHouse server for development, and creates managed ClickHouse Cloud services for production (authentication, service creation, schema migration, application connection). Use when the user wants to build an application with ClickHouse, set up a local ClickHouse dev environment, create tables and start querying, deploy ClickHouse to production or ClickHouse Cloud, or migrate from a local setup to the cloud.
- [Infra Postgres](https://skillsagentes.com/skills/clickhouse/agent-skills/infra-postgres.md): Sets up and manages Postgres using the clickhousectl CLI — runs a local Docker-backed Postgres for development, and creates and operates managed ClickHouse Cloud Postgres services (connections, TLS, runtime config, read replicas, failover, point-in-time restore). Use when the user wants a Postgres or PostgreSQL database for their application, a local Postgres dev environment, psql access, or a managed/production Postgres in ClickHouse Cloud, or mentions moving a local Postgres to production.
- [Clickstack Otel Collector](https://skillsagentes.com/skills/clickhouse/agent-skills/clickstack-otel-collector.md): Use when a user wants to wire an OpenTelemetry collector into a Managed ClickStack service on ClickHouse Cloud, either by deploying a new local collector (Docker run or Docker Compose) or by configuring their own existing collector, then send rich synthetic telemetry and verify it is visible in ClickStack.
- [Clickhouse Js Node Troubleshooting](https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-js-node-troubleshooting.md): Troubleshoot and resolve common issues with the ClickHouse Node.js client (@clickhouse/client). Use this skill whenever a user reports errors, unexpected behavior, or configuration questions involving the Node.js client specifically — including socket hang-up errors, Keep-Alive problems, stream handling issues, data type mismatches, read-only user restrictions, proxy/TLS setup problems, or long-running query timeouts. Trigger even when the user hasn't precisely named the issue; vague symptoms like "my inserts keep failing" or "connection drops randomly" in a Node.js context are strong signals to use this skill. Do NOT use for browser/Web client issues.

## Skills relacionadas

- [Chdb Datastore](https://skillsagentes.com/skills/clickhouse/agent-skills/chdb-datastore.md): Use when the user has tabular data (pandas DataFrame, parquet, csv, Arrow, json) and wants to filter, group, aggregate, join, or speed up slow pandas. Provides chDB DataStore — same pandas API, ClickHouse engine underneath. Also handles reading from S3, MySQL, PostgreSQL, MongoDB, ClickHouse Cloud, Iceberg, Delta Lake as DataFrames and joining across sources. TRIGGER when: user mentions DataFrame, parquet, csv, "fast pandas", "speed up pandas", or cross-source DataFrame joins; user imports `chdb.datastore` or `from datastore import DataStore`. SKIP this skill for raw SQL syntax (use chdb-sql instead), ClickHouse server administration, or non-Python DataStore API work.
- [Chdb Sql](https://skillsagentes.com/skills/clickhouse/agent-skills/chdb-sql.md): Use when the user wants to run SQL — especially analytical SQL — on local files (parquet/csv/json), URLs, S3 paths, or remote databases (Postgres, MySQL, MongoDB, ClickHouse Cloud, Iceberg, Delta Lake) without setting up a server. Provides chDB — embedded ClickHouse SQL in Python with 1000+ functions, Session for stateful multi-step pipelines, parametrized queries, and cross-source joins via `s3()`, `mysql()`, `postgresql()`, `iceberg()`, `deltaLake()`, `remoteSecure()` table functions. TRIGGER when: user wants SQL on parquet/csv/files or across remote analytical sources; uses ClickHouse SQL features (window functions, windowFunnel, geoToH3, JSON path ops, Session, parametrized queries); imports `chdb` or calls `chdb.query()`. SKIP this skill for pandas-style DataFrame method-chaining (use chdb-datastore instead) or ClickHouse server administration.
- [Clickhouse Architecture Advisor](https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-architecture-advisor.md): MUST USE when designing ClickHouse architectures, selecting between ingestion or modeling patterns, or translating best practices into workload-specific system designs. Complements clickhouse-best-practices with decision frameworks and explicit provenance labels.
- [Clickhouse Js Node Coding](https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-js-node-coding.md): Write idiomatic application code with the ClickHouse Node.js client (`@clickhouse/client`). Use this skill whenever a user is *building* against the Node.js client — configuring the client, pinging, inserting rows in JSON or raw formats, selecting and parsing results, binding query parameters, managing sessions and temporary tables, working with data types or customizing JSON parsing. Do NOT use for browser/Web client code.
- [Clickhouse Js Node Rowbinary](https://skillsagentes.com/skills/clickhouse/agent-skills/clickhouse-js-node-rowbinary.md): Generate TypeScript/JavaScript code that reads/decodes AND writes/encodes ClickHouse RowBinary streams for the ClickHouse HTTP server. Use this skill whenever a user wants to parse or produce `RowBinary`, `RowBinaryWithNames`, or `RowBinaryWithNamesAndTypes`. Node.js only, doesn't cover browsers.

---

Skills Agentes · [Índice de páginas en markdown](https://skillsagentes.com/sitemap.md) · [Inicio](https://skillsagentes.com/index.md)