dbHash
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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 acrossmongod
instances, such as across members of replica sets.The
dbHash
command obtains a shared (S) lock on the database, which prevents writes until the command completes.dbHash
has the following syntax:db.runCommand ( { dbHash: 1, collections: [ <collection1>, ... ] } ) FieldTypeDescriptiondbHash
Any typeThe command to run. Specify any value.collections
arrayOptional. 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
Non-Existent Collection
If a collection in the collections
array is non-existent,
dbHash
does not return a hash value for that collection.
Restrictions
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 | 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.
| |||||
capped | An array that lists the capped collections. | |||||
uuids | A document with the collections and their corresponding UUID values.
| |||||
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") } } }