mycoll.count() db.mycoll.copyTo(newColl) - duplicates collection by copying all documents to newColl; no indexes are copied. db.mycoll.convertToCapped(maxBytes) - calls {convertToCapped:'mycoll', size:maxBytes}}
demo.count( query = {}, <optional params> ) - 计算匹配查询的文档数量,可选参数有:limit、skip、hint、maxTimeMS db.demo.countDocuments( query = {}, <optional params> ) - count the number of documents that matches the query, optional parameters are: limit, skip, hint, maxTimeMS db.demo...
显示mongodb如何找到返回的文档,可以确定慢查询的原因,进而确定是否添加索引或者是优化数据就地更新信息: 只有在必要的时候才会写磁盘。例如某键值1秒内被更新多次,则会进行写磁盘存储二进制数据:BSON支持在一个文档中存储最多4MB的二进制数据,电影、音频也可以存储 05章 安装mongodb 1.下载二进制版本 开箱即用版本 ...
> db.mycoll.help() DBCollection help db.mycoll.find().help() - show DBCursor help db.mycoll.count() db.mycoll.copyTo(newColl) - duplicates collection by copying all documents to newColl; no indexes are copied. db.mycoll.convertToCapped(maxBytes) - calls {convertToCapped:'mycoll', ...
{name:"Jerry"})//返回数组db.test.findOne({name:"Jerry"})//返回对象db.test.find({}).count()//数量 或 db.test.count()db.users.count({age:{$gt:25}})//条件数量db.test.find({age:{$gt:25}})//大于 或者 $gte 即 >=db.test.find({create_ts:{$gt:ISODate("2019-09-19T00:00:...
This returns all operations that lasted longer than 100 milliseconds. Ensure that the value specified here (100, in this example) is above theslowOpThresholdMsthreshold. You must use the$queryoperator to access thequeryfield of documents withinsystem.profile. ...
slowOpSampleRate: 1.0 # 过滤器,记录耗时超过2秒的查询操作 #filter: '{ op: "query", millis: { $gt: 2000 } }' replication: oplogSizeMB: 100 replSetName: shard1 enableMajorityReadConcern: false sharding: clusterRole: shardsvr archiveMovedChunks: false ...
, mongodb maps the authenticated username as the ldap dn. in earlier versions, providing an empty mapping document causes mapping to fail. example the following shows two transformation documents. the first document matches against any string ending in @engineering , placing anything preceeding the ...
false. during chunk migration, a shard does not save documents migrated from the shard. auditlog options auditlog: destination: <string> format: <string> path: <string> filter: <string> schema: <string> auditlog.auditencryptionkeyidentifier type : string new in version 6.0 . specifies the ...
db.person.find({}).count(); Asort() methodreturns the documents in any order you prefer such as by name in reverse alphabetical order: db.person.find({}).sort({name:-1}); You can also limit the number of documents returned, e.g. find the first three names: ...