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DOCSP-33843 drop hashed shard key index (#5746)
* DOCSP-33843 drop hashed shard key index * typo * internal review * internal review * external review * replace cleanupOrphaned with shardedDataDistribution * starting in 6.0.3
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‎source/administration/sharded-cluster-administration.txt‎

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/tutorial/backup-sharded-cluster-metadata
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/tutorial/convert-sharded-cluster-to-replica-set
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/tutorial/convert-replica-set-to-replicated-shard-cluster
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/tutorial/drop-a-hashed-shard-key-index
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:doc:`Config Server Administration </administration/sharded-cluster-config-servers>`
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This section contains articles and tutorials related to sharded
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Convert a replica set to a sharded cluster in which each shard is
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its own replica set.
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:doc:`/tutorial/drop-a-hashed-shard-key-index`
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Drop a Hashed Shard Key Index.

‎source/core/hashed-sharding.txt‎

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:ref:`pre-define-zone-range-hashed-example`.
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Drop a Hashed Shard Key Index
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. include:: /includes/drop-hashed-shard-key-index.rst
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.. seealso::

‎source/includes/drop-hashed-shard-key-index-main.rst‎

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Starting in MongoDB 7.0.3 (and 6.0.12 and 5.0.22), you can drop the
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index for a hashed shard key.
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This can speed up data insertion for collections sharded with a hashed
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shard key. It can also speed up data ingestion when using
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``mongosync``.
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‎source/includes/drop-hashed-shard-key-index.rst‎

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.. include:: /includes/drop-hashed-shard-key-index-main.rst
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For details, see :ref:`drop-a-hashed-shard-key-index`.

‎source/includes/shardedDataDistribution-output-example.rst‎

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.. code-block:: json
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[
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{
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"ns": "test.names",
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"shards": [
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{
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"shardName": "shard-1",
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"numOrphanedDocs": 0,
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"numOwnedDocuments": 6,
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"ownedSizeBytes": 366,
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"orphanedSizeBytes": 0
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},
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{
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"shardName": "shard-2",
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"numOrphanedDocs": 0,
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"numOwnedDocuments": 6,
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"ownedSizeBytes": 366,
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"orphanedSizeBytes": 0
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}
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]
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}
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]
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‎source/reference/operator/aggregation/shardedDataDistribution.txt‎

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Example output:
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.. code-block:: json
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[
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{
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"ns": "test.names",
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"shards": [
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{
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"shardName": "shard-1",
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"numOrphanedDocs": 0,
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"numOwnedDocuments": 6,
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"ownedSizeBytes": 366,
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"orphanedSizeBytes": 0
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},
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{
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"shardName": "shard-2",
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"numOrphanedDocs": 0,
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"numOwnedDocuments": 6,
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"ownedSizeBytes": 366,
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"orphanedSizeBytes": 0
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}
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]
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}
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]
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.. include:: /includes/shardedDataDistribution-output-example.rst

‎source/release-notes/7.0.txt‎

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General Changes
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---------------
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Drop a Hashed Shard Key Index
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. include:: /includes/drop-hashed-shard-key-index.rst
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Cache Refresh Time Fields
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~~~~~~~~~~~~~~~~~~~~~~~~~
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‎source/tutorial/drop-a-hashed-shard-key-index.txt‎

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.. _drop-a-hashed-shard-key-index:
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=============================
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Drop a Hashed Shard Key Index
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=============================
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.. default-domain:: mongodb
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.. contents:: On this page
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:local:
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:backlinks: none
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:depth: 1
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:class: singlecol
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.. include:: /includes/drop-hashed-shard-key-index-main.rst
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About this Task
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---------------
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Dropping an `unnecessary index
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<http://www.mongodb.com/developer/products/mongodb/schema-design-anti-pattern-unnecessary-indexes/>`_
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can speed up CRUD operations. Each CRUD operation has to update all the
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indexes related to a document. Removing one index can increase the
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speed of all CRUD operations.
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When you drop a hashed shard key index, the server disables balancing
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for that collection and excludes the collection from future balancing
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rounds. In order to include the collection in balancing rounds once
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again, you must recreate the shard key index.
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Steps
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-----
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.. procedure::
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:style: normal
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.. step:: Stop the balancer
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Run the following command to stop the balancer:
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.. code-block:: javascript
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sh.stopBalancer()
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You can only run ``sh.stopBalancer()`` on ``mongos``.
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``sh.stopBalancer()`` produces an error if run on ``mongod``.
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.. step:: Confirm there are no orphaned documents in your collection
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Starting in MongoDB 6.0.3, you can run an aggregation using the
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:pipeline:`$shardedDataDistribution` stage to confirm no orphaned
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documents remain:
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.. code-block:: javascript
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db.aggregate([
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{ $shardedDataDistribution: {} },
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{ $match: { "ns": "<database>.<collection>" } }
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])
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``$shardedDataDistribution`` has output similar to the following:
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.. include:: /includes/shardedDataDistribution-output-example.rst
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Ensure that ``"numOrphanedDocs"`` is ``0`` for each shard in the
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cluster.
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.. step:: Drop the hashed shard key index
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Run the following command to drop the index:
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.. code-block:: javascript
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db.collection.dropIndex("<index name>")
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.. step:: Restart the balancer
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Run the following command to restart the balancer on the cluster:
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.. code-block:: javascript
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sh.startBalancer()
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Learn More
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----------
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- :ref:`sharding-hashed`
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- :ref:`sharding-balancing`
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- :method:`db.collection.dropIndex()`
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- :method:`sh.stopBalancer()`
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- :method:`sh.startBalancer()`
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- :method:`sh.getBalancerState()`
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