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dbHash

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.

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

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.

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.

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")
}
}
}

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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