Clickhouse Io

ClickHouse 分析模式 (ClickHouse Analytics Patterns)

针对高性能分析和数据工程的 ClickHouse 特定模式。

何时激活 (When to Activate)

• 设计 ClickHouse 表结构（MergeTree 引擎选择）
• 编写分析查询（聚合、窗口函数、连接）
• 优化查询性能（分区剪枝、投影、物化视图）
• 摄取海量数据（批量插入、Kafka 集成）
• 将分析业务从 PostgreSQL/MySQL 迁移到 ClickHouse
• 实现实时仪表盘或时间序列分析

概述 (Overview)

ClickHouse 是一款用于联机分析处理（OLAP）的列式数据库管理系统（DBMS）。它针对大型数据集的高速分析查询进行了优化。

核心特性：

• 列式存储
• 数据压缩
• 并行查询执行
• 分布式查询
• 实时分析

表设计模式 (Table Design Patterns)

MergeTree 引擎（最常用）

CREATE TABLE markets_analytics (
    date Date,
    market_id String,
    market_name String,
    volume UInt64,
    trades UInt32,
    unique_traders UInt32,
    avg_trade_size Float64,
    created_at DateTime
) ENGINE = MergeTree()
PARTITION BY toYYYYMM(date)
ORDER BY (date, market_id)
SETTINGS index_granularity = 8192;

ReplacingMergeTree（去重）

-- 针对可能存在重复的数据（例如来自多个源）
CREATE TABLE user_events (
    event_id String,
    user_id String,
    event_type String,
    timestamp DateTime,
    properties String
) ENGINE = ReplacingMergeTree()
PARTITION BY toYYYYMM(timestamp)
ORDER BY (user_id, event_id, timestamp)
PRIMARY KEY (user_id, event_id);

AggregatingMergeTree（预聚合）

-- 用于维护聚合指标
CREATE TABLE market_stats_hourly (
    hour DateTime,
    market_id String,
    total_volume AggregateFunction(sum, UInt64),
    total_trades AggregateFunction(count, UInt32),
    unique_users AggregateFunction(uniq, String)
) ENGINE = AggregatingMergeTree()
PARTITION BY toYYYYMM(hour)
ORDER BY (hour, market_id);

-- 查询聚合数据
SELECT
    hour,
    market_id,
    sumMerge(total_volume) AS volume,
    countMerge(total_trades) AS trades,
    uniqMerge(unique_users) AS users
FROM market_stats_hourly
WHERE hour >= toStartOfHour(now() - INTERVAL 24 HOUR)
GROUP BY hour, market_id
ORDER BY hour DESC;

查询优化模式 (Query Optimization Patterns)

高效过滤

-- ✅ 推荐：优先使用索引列
SELECT *
FROM markets_analytics
WHERE date >= '2025-01-01'
  AND market_id = 'market-123'
  AND volume > 1000
ORDER BY date DESC
LIMIT 100;

-- ❌ 不推荐：先对非索引列进行过滤
SELECT *
FROM markets_analytics
WHERE volume > 1000
  AND market_name LIKE '%election%'
  AND date >= '2025-01-01';

聚合 (Aggregations)

-- ✅ 推荐：使用 ClickHouse 特有的聚合函数
SELECT
    toStartOfDay(created_at) AS day,
    market_id,
    sum(volume) AS total_volume,
    count() AS total_trades,
    uniq(trader_id) AS unique_traders,
    avg(trade_size) AS avg_size
FROM trades
WHERE created_at >= today() - INTERVAL 7 DAY
GROUP BY day, market_id
ORDER BY day DESC, total_volume DESC;

-- ✅ 使用 quantile 计算百分位数（比 percentile 更高效）
SELECT
    quantile(0.50)(trade_size) AS median,
    quantile(0.95)(trade_size) AS p95,
    quantile(0.99)(trade_size) AS p99
FROM trades
WHERE created_at >= now() - INTERVAL 1 HOUR;

窗口函数 (Window Functions)

-- 计算累计总量
SELECT
    date,
    market_id,
    volume,
    sum(volume) OVER (
        PARTITION BY market_id
        ORDER BY date
        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    ) AS cumulative_volume
FROM markets_analytics
WHERE date >= today() - INTERVAL 30 DAY
ORDER BY market_id, date;

数据插入模式 (Data Insertion Patterns)

批量插入（推荐）

import { ClickHouse } from 'clickhouse'

const clickhouse = new ClickHouse({
  url: process.env.CLICKHOUSE_URL,
  port: 8123,
  basicAuth: {
    username: process.env.CLICKHOUSE_USER,
    password: process.env.CLICKHOUSE_PASSWORD
  }
})

// ✅ 批量插入（高效）
async function bulkInsertTrades(trades: Trade[]) {
  const values = trades.map(trade => `(
    '${trade.id}',
    '${trade.market_id}',
    '${trade.user_id}',
    ${trade.amount},
    '${trade.timestamp.toISOString()}'
  )`).join(',')

  await clickhouse.query(`
    INSERT INTO trades (id, market_id, user_id, amount, timestamp)
    VALUES ${values}
  `).toPromise()
}

// ❌ 逐条插入（缓慢）
async function insertTrade(trade: Trade) {
  // 切勿在循环中这样做！
  await clickhouse.query(`
    INSERT INTO trades VALUES ('${trade.id}', ...)
  `).toPromise()
}

流式插入 (Streaming Insert)

// 用于持续的数据摄取
import { createWriteStream } from 'fs'
import { pipeline } from 'stream/promises'

async function streamInserts() {
  const stream = clickhouse.insert('trades').stream()

  for await (const batch of dataSource) {
    stream.write(batch)
  }

  await stream.end()
}

物化视图 (Materialized Views)

实时聚合

-- 为每小时统计创建物化视图
CREATE MATERIALIZED VIEW market_stats_hourly_mv
TO market_stats_hourly
AS SELECT
    toStartOfHour(timestamp) AS hour,
    market_id,
    sumState(amount) AS total_volume,
    countState() AS total_trades,
    uniqState(user_id) AS unique_users
FROM trades
GROUP BY hour, market_id;

-- 查询该物化视图
SELECT
    hour,
    market_id,
    sumMerge(total_volume) AS volume,
    countMerge(total_trades) AS trades,
    uniqMerge(unique_users) AS users
FROM market_stats_hourly
WHERE hour >= now() - INTERVAL 24 HOUR
GROUP BY hour, market_id;

性能监控 (Performance Monitoring)

查询性能

-- 检查慢查询
SELECT
    query_id,
    user,
    query,
    query_duration_ms,
    read_rows,
    read_bytes,
    memory_usage
FROM system.query_log
WHERE type = 'QueryFinish'
  AND query_duration_ms > 1000
  AND event_time >= now() - INTERVAL 1 HOUR
ORDER BY query_duration_ms DESC
LIMIT 10;

表统计信息

-- 检查表大小
SELECT
    database,
    table,
    formatReadableSize(sum(bytes)) AS size,
    sum(rows) AS rows,
    max(modification_time) AS latest_modification
FROM system.parts
WHERE active
GROUP BY database, table
ORDER BY sum(bytes) DESC;

常用分析查询 (Common Analytics Queries)

时间序列分析

-- 日活跃用户 (DAU)
SELECT
    toDate(timestamp) AS date,
    uniq(user_id) AS daily_active_users
FROM events
WHERE timestamp >= today() - INTERVAL 30 DAY
GROUP BY date
ORDER BY date;

-- 留存分析
SELECT
    signup_date,
    countIf(days_since_signup = 0) AS day_0,
    countIf(days_since_signup = 1) AS day_1,
    countIf(days_since_signup = 7) AS day_7,
    countIf(days_since_signup = 30) AS day_30
FROM (
    SELECT
        user_id,
        min(toDate(timestamp)) AS signup_date,
        toDate(timestamp) AS activity_date,
        dateDiff('day', signup_date, activity_date) AS days_since_signup
    FROM events
    GROUP BY user_id, activity_date
)
GROUP BY signup_date
ORDER BY signup_date DESC;

漏斗分析 (Funnel Analysis)

-- 转化漏斗
SELECT
    countIf(step = 'viewed_market') AS viewed,
    countIf(step = 'clicked_trade') AS clicked,
    countIf(step = 'completed_trade') AS completed,
    round(clicked / viewed * 100, 2) AS view_to_click_rate,
    round(completed / clicked * 100, 2) AS click_to_completion_rate
FROM (
    SELECT
        user_id,
        session_id,
        event_type AS step
    FROM events
    WHERE event_date = today()
)
GROUP BY session_id;

同期群分析 (Cohort Analysis)

-- 按注册月份划分的用户同期群
SELECT
    toStartOfMonth(signup_date) AS cohort,
    toStartOfMonth(activity_date) AS month,
    dateDiff('month', cohort, month) AS months_since_signup,
    count(DISTINCT user_id) AS active_users
FROM (
    SELECT
        user_id,
        min(toDate(timestamp)) OVER (PARTITION BY user_id) AS signup_date,
        toDate(timestamp) AS activity_date
    FROM events
)
GROUP BY cohort, month, months_since_signup
ORDER BY cohort, months_since_signup;

数据管道模式 (Data Pipeline Patterns)

ETL 模式

// 提取 (Extract), 转换 (Transform), 加载 (Load)
async function etlPipeline() {
  // 1. 从源端提取
  const rawData = await extractFromPostgres()

  // 2. 转换
  const transformed = rawData.map(row => ({
    date: new Date(row.created_at).toISOString().split('T')[0],
    market_id: row.market_slug,
    volume: parseFloat(row.total_volume),
    trades: parseInt(row.trade_count)
  }))

  // 3. 加载到 ClickHouse
  await bulkInsertToClickHouse(transformed)
}

// 定期运行
setInterval(etlPipeline, 60 * 60 * 1000)  // 每小时一次

变更数据捕获 (CDC)

// 监听 PostgreSQL 变更并同步到 ClickHouse
import { Client } from 'pg'

const pgClient = new Client({ connectionString: process.env.DATABASE_URL })

pgClient.query('LISTEN market_updates')

pgClient.on('notification', async (msg) => {
  const update = JSON.parse(msg.payload)

  await clickhouse.insert('market_updates', [
    {
      market_id: update.id,
      event_type: update.operation,  // INSERT, UPDATE, DELETE
      timestamp: new Date(),
      data: JSON.stringify(update.new_data)
    }
  ])
})

最佳实践 (Best Practices)

1. 分区策略 (Partitioning Strategy)

• 按时间分区（通常为月或日）
• 避免过多分区（会影响性能）
• 使用 DATE 类型作为分区键

2. 排序键 (Ordering Key)

• 将最常过滤的列放在前面
• 考虑基数（高基数列在前）
• 排序方式会影响压缩效果

3. 数据类型 (Data Types)

• 使用最小且合适的类型（UInt32 vs UInt64）
• 对重复出现的字符串使用 LowCardinality
• 对分类数据使用 Enum

4. 避免 (Avoid)

• 使用 SELECT *（应指定具体列）
• 使用 FINAL（应在查询前合并数据）
• 过多的 JOIN（分析场景应进行反规范化）
• 频繁的小批量插入（应改用批量插入）

5. 监控 (Monitoring)

• 跟踪查询性能
• 监控磁盘使用情况
• 检查合并操作 (merge operations)
• 查看慢查询日志

记住：ClickHouse 在分析型负载方面表现卓越。请根据你的查询模式设计表结构，采用批量插入，并利用物化视图进行实时聚合。