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dbHash.txt
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dbHash.txt
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======
dbHash
======
.. default-domain:: mongodb
.. contents:: On this page
:local:
:backlinks: none
:depth: 1
:class: singlecol
Definition
----------
.. dbcommand:: dbHash
Returns the hash values of the collections in a database and an
MD5 value for the list of collections. :dbcommand:`dbHash` is useful
to compare databases across :binary:`~bin.mongod` instances, such as
mirrored :doc:`config servers
</core/sharded-cluster-config-servers>` for sharded clusters or
members of replica sets.
:dbcommand:`dbHash` has the following syntax:
.. code-block:: javascript
db.runCommand ( { dbHash: 1, collections: [ <collection1>, ... ] } )
.. list-table::
:header-rows: 1
:widths: 20 20 80
* - 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,
:dbcommand:`dbHash` does not return a hash value for that collection.
Examples
--------
Return Hash Values for All Collections in a Database
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The following example returns the hash value for all collections in the
database ``test``:
.. code-block:: javascript
use test
db.runCommand( { dbHash: 1 } )
The operation returns the following document:
.. code-block:: json
{
"host" : "myHostName.local",
"collections" : {
"bar" : "0a8089b7134801ab74d5f1310c27f161",
"foo" : "f49ff19aa6959d96b43961a595ae550e",
"foo2" : "a4f0e61c26af65d7efa0d0ad173db801",
"inventory" : "4f6d23309dcc059232d0e4383fcedfa1",
"orders" : "083def5adf48686a732ee07b8ffaf228",
"restaurants" : "407a4f24cfafa40641e20098929c5632",
"zipcodes" : "679530b9b79d529d79bd143435135f25"
},
"md5" : "2e3b201903d60cdc1eedfd58f4c014d4",
"timeMillis" : 71,
"fromCache" : [ ],
"ok" : 1
}
Return Hash Values for Specified Collections in a Database
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The following example returns the hash value for the collections ``foo``
and ``bar`` in the database ``test``:
.. code-block:: javascript
use test
db.runCommand( { dbHash: 1, collections: [ "foo", "bar" ] } )
The operation returns the following document:
.. code-block:: json
{
"host" : "myHostName.local",
"collections" : {
"bar" : "0a8089b7134801ab74d5f1310c27f161",
"foo" : "f49ff19aa6959d96b43961a595ae550e"
},
"md5" : "94f296621d5ed4ed35088257ce0c9d99",
"timeMillis" : 0,
"fromCache" : [ ],
"ok" : 1
}
.. note::
The ``md5`` is the aggregate hash value
of the specified collections.
.. slave-ok, read-lock