dbHash (original) (raw)
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.
Warning
The dbHash command obtains a shared (S) lock on the database, which prevents writes until the command completes.
This command is available in deployments hosted in the following environments:
- MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
Important
This command is not supported in M0, M2, M5, and Flex clusters or in serverless instances. For more information, see Unsupported Commands.
- MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
- MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
The command has the following syntax:
db.runCommand(
{
dbHash: 1,
collections: [ <collection1>, ... ]
}
)
The command takes the following fields:
| 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.
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. |
| uuids | A document with the collections and their corresponding UUID values.{ <collection1>: <UUID1>, <collection2>: <UUID2>, ...} |
| md5 | The aggregate hash value for these collections. |
| timeMillis | Number of milliseconds to generate the hash. |
| okoperationTime$clusterTime | Returned with every command. See also Responsefor details. |
The following example returns the hash value for all collections in the database test:
use test
db.runCommand( { dbHash: 1 } )
The operation returns the following document:
{
"host" : "myHostName.local:27017",
"collections" : {
"foo" : "d27b769230edc551d869060ec3fb68bd",
"inventory" : "ec3d821581ea1bd3aa8196c94b946874",
"log" : "d41d8cd98f00b204e9800998ecf8427e",
"orders" : "0242c0a128c284ea9576a34db2306c12",
"restaurants" : "5dc9b88091c36f0d529567b5b6e3fc92",
"zipcodes" : "31ede812bf397509a87359c65bf2a08c"
},
"capped" : [
"log"
],
"uuids" : {
"foo" : UUID("469592fe-3bfe-425e-975f-cedbe0c4741d"),
"inventory" : UUID("0830e0ad-cc24-4fc7-80d0-8e22fe45e382"),
"log" : UUID("4be024ff-711b-4ab8-836b-dee662e090f1"),
"orders" : UUID("755be489-745f-400c-ac3b-f27525ad0108"),
"restaurants" : UUID("520b56ec-3276-4904-b6e5-286bc9bfa648"),
"zipcodes" : UUID("12e97b70-c174-40af-a178-5d83a241fe20")
},
"md5" : "0cb7417ae9d9eb865000b4debdc671da",
"timeMillis" : 53,
"ok" : 1,
"operationTime" : Timestamp(1529208582, 4),
"$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 inventoryand 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")
}
}
}