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. dbHash is useful to compare databases across mongod instances, such as across members of replica sets.

dbHash has the following syntax:语法如下所示：

db.runCommand ( { dbHash: 1, collections: [ <collection1>, ... ] } )
Field字段Type类型Description描述
dbHash Any type The command to run. Specify any value.
collections array

Optional.可选。An array of collection names.

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.

Behavior行为

Non-Existent Collection

If a collection in the collections array is non-existent, dbHash does not return a hash value for that collection.

Restrictions

MongoDB drivers automatically set afterClusterTime for operations associated with causally consistent sessions. Starting in MongoDB 4.2, the dbHash command no longer support afterClusterTime. As such, dbHash cannot be associated with causally consistent sessions.

Return Document

The command returns a document with the following fields:

Field字段Description描述
host The host and port of the mongod instance on which the command is run.
collections

A document with the collections and their corresponding hash values.

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

An array that lists the capped collections.

New in version 4.0.版本4.0中的新功能。

uuids

A document with the collections and their corresponding UUID values.

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

New in version 4.0.版本4.0中的新功能。

md5 The aggregate hash value for these collections.
timeMillis Number of milliseconds to generate the hash.
ok
operationTime
$clusterTime
 Returned with every command. See also Response for details.

Examples示例

Return Hash Values for All Collections in a Database

The following example returns the hash value for all collections in the database test:

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

The operation returns the following document:

{
   "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

The following example returns the hash value for the collections inventory and orders in the database test:

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

The operation returns the following document:

{
   "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")
      }
   }
}