MongoDB，通过正则表达式对索引字段进行查询的性能 [英] MongoDB, performance of query by regular expression on indexed fields

问题描述

我想按名称查找帐户(在 50K 帐户的 MongoDB 集合中)

通常的方式:我们用字符串查找

db.accounts.find({ name: 'Jon Skeet' })  // indexes help improve performance!

正则表达式怎么样?手术费用高吗?

db.accounts.find( { name: /Jon Skeet/ }) // worry! how indexes work with regex?

<小时>

根据 WiredPrairie:
MongoDB 使用 RegEx 的 prefix 来查找索引(例如:/^prefix.*/):

According to WiredPrairie:
MongoDB use prefix of RegEx to lookup indexes (ex: /^prefix.*/):

db.accounts.find( { name: /^Jon Skeet/ })  // indexes will help!'

MongoDB $regex

推荐答案

其实根据文档，

如果该字段存在索引，则 MongoDB 匹配正则针对索引中的值的表达式，这可能比 a集合扫描.如果常规的可以进行进一步的优化表达式是一个前缀表达式"，这意味着所有潜在的匹配以相同的字符串开始.这允许 MongoDB 构建一个来自该前缀的范围"，并且只匹配来自位于该范围内的索引.

If an index exists for the field, then MongoDB matches the regular expression against the values in the index, which can be faster than a collection scan. Further optimization can occur if the regular expression is a "prefix expression", which means that all potential matches start with the same string. This allows MongoDB to construct a "range" from that prefix and only match against those values from the index that fall within that range.

http://docs.mongodb.org/手册/参考/操作员/查询/正则表达式/#index-use

换句话说:

对于 /Jon Skeet/ regex ，mongo 将完整扫描索引中的键，然后获取匹配的文档，这比集合扫描更快.

For /Jon Skeet/ regex ,mongo will full scan the keys in the index then will fetch the matched documents, which can be faster than collection scan.

对于 /^Jon Skeet/ regex ，mongo 将只扫描索引中以正则表达式开头的范围，这样会更快.

For /^Jon Skeet/ regex ,mongo will scan only the range that start with the regex in the index, which will be faster.

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