MongoDB’saggregate()function may count several fields. As a result, the fields are counted using$count. Below is an example where a timestamp is utilized for only one entry. Some documents can be saved in thestudentcollection in this example, and you can use thefind()method to see how ...
插入数据后,使用 Studio 3T 查看数据量时,发现显示的 count 结果与插入的数据不一致,偶然会多出几条或十几条 通过谷歌发现,官方文档——(https://docs.mongodb.com/manual/reference/method/db.collection.count/)中有解释这种现象: On a sharded cluster, db.collection.count() can result in an inaccurate ...
而MongoDB3.6官方文档却是这么描述的 On a sharded cluster, db.collection.count() can result in an inaccurate count if orphaned documents exist or if a chunk migration is in progress. To avoid these situations, on a sharded cluster, use the db.collection.aggregate() method 也就是说,MongoDB4.0...
To avoid these situations, on a sharded cluster, use the db.collection.aggregate() method: You can use the $count stage to count the documents. For example, the following operation counts the documents in a collection: db.collection.aggregate( [ { $count: "myCount" } ]) The $count stag...
如果将级别设置为"majority",你必须使用WiredTiger存储引擎,并且在启动mongod实例时指定--enableMajorityReadConcern参数)(或者在config参数配置文档中指定replication.enableMajorityReadConcern参数)。 博文参考:MongoDB readConcern 原理解析 Only replica sets using protocol version 1 support "majority" read concern. Rep...
db.table3.count() 使用该命令依然会出现统计信息不准确的现象,通过谷歌发现,官方文档——(https://docs.mongodb.com/manual/reference/method/db.collection.count/)中有解释这种现象: On a sharded cluster,db.collection.count()can result in aninaccuratecount iforphaned documentsexist or if achunk migration...
in MongoDB is an array, which can store multiple values in a single field. When working with arrays in MongoDB, you may need to query and count the number of elements in an array. In this article, we will explore how to perform an array count query in MongoDB using thecountmethod. ...
The db.collection.countDocuments method internally uses an aggregation query to return the document count while db.collection.estimatedDocumentCount/ returns documents count based on metadata. It is worth mentioning that the estimatedDocumentCount output can be inaccurate as mentioned in the documentation...
To avoid these situations, on a sharded cluster, use the db.collection.aggregate() method 也就是说,MongoDB4.0分片集群模式下,针对不带谓词条件的全表count操作的返回结果是不准确的,主要包括以下两种场景。在MongoDB4.0以前的版本,即使不带谓词条件,在以下两种场景下count值也不准。
现在可以在MongoCollection中找到计数方法：