mongodb 中 OR+Sort 查询的复合索引

问题描述：

对于这个 OR 查询:

For this OR query:

db.messages.find({ $or: [ { to: { $ne: null }, from: "xyz" }, { to: "xyz" } ] }).sort({_id: -1}).limit(50)

具有以下索引:

{to:1, from: 1, _id:-1} and {from:1, to:1, _id:-1}

mongo 总是进行全面扫描.

mongo is always doing a full scan.

我希望 mongo 可以使用这两个索引并合并结果.

I was hoping that mongo could use these two indices and merge the results.

我是否需要将其拆分为两个查询(每个 OR 子句一个)并自行合并?或者是否有其他索引可以提供帮助?

Do I need to split this into two queries (one for each OR clause) and merge myself? Or is there some other index that can help?

答

这是一个已知问题，https://jira.mongodb.org/browse/SERVER-1205，如果它对您的用例非常重要，您可以投票.

This is a known issue, https://jira.mongodb.org/browse/SERVER-1205, which you can vote for if it is very important for your use case.