dbHash

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Definition定义

dbHash

Returns the hash values of the collections in a database and an MD5 value for these collections. 返回数据库中集合的哈希值和这些集合的MD5值。dbHash is useful to compare databases across mongod instances, such as across members of replica sets.dbHash对于跨mongod实例（例如跨副本集的成员）比较数据库非常有用。

dbHash has the following syntax:具有以下语法：

db.runCommand ( { dbHash: 1, collections: [ <collection1>, ... ] } )
Field字段Type类型Description描述
dbHashAny typeThe command to run. 要运行的命令。Specify any value.指定任意值。
collectionsarray

Optional. 可选。An array of collection names.集合名称的数组。

Either specify the collections for which to return the hash values, or omit or specify an empty array to return the hash values for all collections in the database.指定要返回其哈希值的集合，或者忽略或指定空数组以返回数据库中所有集合的哈希值。

Behavior行为

Non-Existent Collection不存在的集合

If a collection in the collections array is non-existent, dbHash does not return a hash value for that collection.如果collections数组中的集合不存在，则dbHash不会返回该集合的哈希值。

Restrictions限制

MongoDB drivers automatically set afterClusterTime for operations associated with causally consistent sessions. MongoDB驱动程序自动为与因果一致会话相关的操作设置afterClusterTime。Starting in MongoDB 4.2, the dbHash command no longer support afterClusterTime. 从MongoDB 4.2开始，dbHash命令不再支持afterClusterTime。As such, dbHash cannot be associated with causally consistent sessions.因此，dbHash不能与因果一致的会话相关联。

Return Document退货单据

The command returns a document with the following fields:该命令返回包含以下字段的文档：

Field字段Description描述
hostThe host and port of the mongod instance on which the command is run.运行命令的mongod实例的主机和端口。
collections

A document with the collections and their corresponding hash values.包含集合及其相应哈希值的文档。

{
   <collection1>: <hash1>,
   <collection2>: <hash2>,
   ...
}
capped

An array that lists the capped collections.列出封顶集合的数组。

New in version 4.0.在版本4.0中新增。

uuids

A document with the collections and their corresponding UUID values.包含集合及其相应UUID值的文档。

{
   <collection1>: <UUID1>,
   <collection2>: <UUID2>,
   ...
}

New in version 4.0.在版本4.0中新增。

md5The aggregate hash value for these collections.这些集合的聚合哈希值。
timeMillisNumber of milliseconds to generate the hash.生成哈希的毫秒数。
ok
operationTime
$clusterTime
Returned with every command. 随每个命令返回。See also Response for details.有关详细信息，请参阅响应。

Examples示例

Return Hash Values for All Collections in a Database返回数据库中所有集合的哈希值

The following example returns the hash value for all collections in the database test:以下示例返回数据库test中所有集合的哈希值：

use test
db.runCommand( { dbHash: 1 } )

The operation returns the following document:该操作返回以下文档：

{
   "host" : "myHostName.local:27017",
   "collections" : {
      "foo" : "d27b769230edc551d869060ec3fb68bd",
      "inventory" : "ec3d821581ea1bd3aa8196c94b946874",
      "log" : "d41d8cd98f00b204e9800998ecf8427e",
      "orders" : "0242c0a128c284ea9576a34db2306c12",
      "restaurants" : "5dc9b88091c36f0d529567b5b6e3fc92",
      "zipcodes" : "31ede812bf397509a87359c65bf2a08c"
   },
   "capped" : [
      "log"
   ],
   "uuids" : {
      "foo" : UUID("469592fe-3bfe-425e-975f-cedbe0c4741d"),
      "inventory" : UUID("0830e0ad-cc24-4fc7-80d0-8e22fe45e382"),
      "log" : UUID("4be024ff-711b-4ab8-836b-dee662e090f1"),
      "orders" : UUID("755be489-745f-400c-ac3b-f27525ad0108"),
      "restaurants" : UUID("520b56ec-3276-4904-b6e5-286bc9bfa648"),
      "zipcodes" : UUID("12e97b70-c174-40af-a178-5d83a241fe20")
   },
   "md5" : "0cb7417ae9d9eb865000b4debdc671da",
   "timeMillis" : 53,
   "ok" : 1,
   "operationTime" : Timestamp(1529208582, 4),
   "$clusterTime" : {
      "clusterTime" : Timestamp(1529208582, 4),
      "signature" : {
         "hash" : BinData(0,"X3MmevDqUgCVvN1AhnT+fiOL/Lc="),
         "keyId" : NumberLong("6567898567824900097")
      }
   }
}

Return Hash Values for Specified Collections in a Database返回数据库中指定集合的哈希值

The following example returns the hash value for the collections inventory and orders in the database test:以下示例返回数据库test中集合inventory和orders的哈希值：

use test
db.runCommand( { dbHash: 1, collections: [ "inventory", "orders" ] } )

The operation returns the following document:该操作返回以下文档：

{
   "host" : "myHostName.local:27017",
   "collections" : {
      "inventory" : "ec3d821581ea1bd3aa8196c94b946874",
      "orders" : "0242c0a128c284ea9576a34db2306c12"
   },
   "capped" : [ ],
   "uuids" : {
      "inventory" : UUID("0830e0ad-cc24-4fc7-80d0-8e22fe45e382"),
      "orders" : UUID("755be489-745f-400c-ac3b-f27525ad0108")
   },
   "md5" : "cb4676f316ff2ff29c701a5edd18afe3",
   "timeMillis" : 0,
   "ok" : 1,
   "operationTime" : Timestamp(1529208801, 1),
   "$clusterTime" : {
      "clusterTime" : Timestamp(1529208801, 1),
      "signature" : {
         "hash" : BinData(0,"I4z4a4Mgs+tcx0MP5xIU8DYAMB0="),
         "keyId" : NumberLong("6567898567824900097")
      }
   }
}
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