ClickHouse TTL 策略与冷热存储迁移实践

创建表与 TTL： ``` CREATE TABLE events ( ts DateTime, uid UInt64, payload String ) ENGINE = MergeTree() PARTITION BY toYYYYMM(ts) ORDER BY (ts, uid) TTL ts + INTERVAL 30 DAY DELETE; ``` 分层存储迁移（需预设 storage policy 与卷）： ``` ALTER TABLE events MODIFY TTL ts + INTERVAL 7 DAY TO VOLUME 'slow', ts + INTERVAL 30 DAY DELETE; ``` 验证 TTL 生效： ``` SELECT count() FROM events WHERE ts < now() - INTERVAL 40 DAY; ```