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• Definition
• Behavior
• Examples

Definition

dbHash

Returns the hash values of the collections in a database and an MD5 value for the list of collections. dbHash is useful to compare databases across mongod instances, such as mirrored config servers for sharded clusters or members of replica sets.

dbHash has the following syntax:

copy

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.

Examples

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

{
   "host" : "myHostName.local",
   "collections" : {
      "bar" : "0a8089b7134801ab74d5f1310c27f161",
      "foo" : "f49ff19aa6959d96b43961a595ae550e",
      "foo2" : "a4f0e61c26af65d7efa0d0ad173db801",
      "inventory" : "4f6d23309dcc059232d0e4383fcedfa1",
      "orders" : "083def5adf48686a732ee07b8ffaf228",
      "restaurants" : "407a4f24cfafa40641e20098929c5632",
      "zipcodes" : "679530b9b79d529d79bd143435135f25"
   },
   "md5" : "2e3b201903d60cdc1eedfd58f4c014d4",
   "timeMillis" : 71,
   "ok" : 1
}

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

{
   "host" : "myHostName.local",
   "collections" : {
      "bar" : "0a8089b7134801ab74d5f1310c27f161",
      "foo" : "f49ff19aa6959d96b43961a595ae550e"
   },
   "md5" : "94f296621d5ed4ed35088257ce0c9d99",
   "timeMillis" : 0,
   "ok" : 1
}