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dbHash

Definition

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:

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

Optional. 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

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

The command returns a document with the following fields:

Field Description
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.

uuids

A document with the collections and their corresponding UUID values.

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

New in version 4.0.

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

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")
      }
   }
}
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