Druid Terms multi-tenant: a single instance of software runs on a server and serves multiple tenants OLAP: Online analytical processing, is an approach to answering multi-dimensional analytical (MDA) queries swiftly in computing SaaS: a software distribution model in which a third-party provider hosts applications and makes them available to customers over the Internet ROLL-UP: 將原始數據在匯入資料庫時就進行彙整處理 Scenario 資料已經整理好，不需要更新操作 不需要做表格的join 對於資料時間維度要求比較高的工作 即時性極重要的project External Dependencies Zookeeper: cluster內部溝通資訊所用 Metadata Storage: 儲存segment的meta data和configuration，提供coordinator node去調配segment的的載入情況 Deep Storage: segment的永久儲存空間，提供Historical node去下載segment