elasticsearch 關聯查詢對比

兩種方式 嵌套和父子關聯

Nested

• Nested docs are stored in the same Lucene block as each other, which helps read/query performance. Reading a nested doc is faster than the equivalent parent/child.

• Updating a single field in a nested document (parent or nested children) forces ES to reindex the entire nested document. This can be very expensive for large nested docs

• "Cross referencing" nested documents is impossible

• Best suited for data that does not change frequently

Parent/Child

• Children are stored separately from the parent, but are routed to the same shard. So parent/children are slightly less performance on read/query than nested

• Parent/child mappings have a bit extra memory overhead, since ES maintains a "join" list in memory

• Updating a child doc does not affect the parent or any other children, which can potentially save a lot of indexing on large docs

• Sorting/scoring can be difficult with Parent/Child since the Has Child/Has Parent operations can be opaque at times

綜上所述，兩種方式均有利弊，官方建議，自己處理關聯關系，減輕ES的壓力。