# 聚合管道和分片集合

在本页面

* [行为](#behavior)
* [优化](#optimization)

聚合管道支持对[分片](/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md)集合的操作。本节介绍特定于[聚合管道](/aggregation/aggregation-pipeline.md)和分片集合的行为。

## 行为

Mongodb 3.2 版本的改变

如果管道以 shard key 上的精确[$match](/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md)开头，则整个管道仅在匹配的分片上运行。以前，管道将被拆分，合并它的工作必须在主分片上完成。

对于必须在多个分片上运行的聚合操作，如果操作不需要在数据库的主分片上运行，则这些操作将会将结果路由到随机分片以合并结果，以避免该数据库的主分片超载。 [$out](/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md)阶段和[$lookup](/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md)阶段需要在数据库的主分片上运行。

## 优化

在将聚合管道分成两部分时，管道被拆分以确保分片在考虑优化的情况下执行尽可能多的阶段。

要查看管道是如何拆分的，请在[db.collection.aggregate()](/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md)方法中包含[explain](/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md)选项。

优化可能会在不同版本之间发生变化。

译者：李冠飞

校对：李冠飞


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.mongoing.com/aggregation/aggregation-pipeline/aggregation-pipeline-and-sharded-collections.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.