DOCS-15911-update-chunkMigrationConcurrency (BACKPORT) (#2613) (#2678)

* DOCS-15911-update-chunkMigrationConcurrency (#2604)

* DOCS-15911-update-chunkMigrationConcurrency

* DOCS-15911-update-chunkMigrationConcurrency

* DOCS-15911-update-chunkMigrationConcurrency

* DOCS-15911-update-chunkMigrationConcurrency

* DOCS-15911-update-chunkMigrationConcurrency

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* DOCS-15911-update-chunkMigrationConcurrency

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Co-authored-by: jason-price-mongodb <[email protected]>
Co-authored-by: jason-price-mongodb <[email protected]>

Author: 3 people

source/reference/command/serverStatus.txt

@@ -4221,6 +4221,16 @@ shardingStatistics
 
    .. versionadded:: 4.4
 
+.. serverstatus:: shardingStatistics.chunkMigrationConcurrency
+
+   The number of threads on the source shard and the receiving shard for
+   performing :ref:`chunk migration <migrate-chunks-sharded-cluster>`
+   operations.
+
+   *Only present when run on a shard.*
+
+   *Available starting in MongoDB 5.0.15.*
+
 .. serverstatus:: shardingStatistics.catalogCache
 
    A document with statistics about the cluster's routing information cache.

source/reference/parameters.txt

@@ -2722,6 +2722,49 @@ Sharding Parameters
    ``AsyncRequestsSenderUseBaton`` and always enables the performance
    enhancement controlled by the parameter.
 
+.. parameter:: chunkMigrationConcurrency
+
+   *Available starting in MongoDB 5.0.15.*
+
+   *Type*: integer
+
+   *Default*: 1
+
+   |both|
+
+   Specifies an integer that sets the number of threads on the source
+   shard and the receiving shard for :ref:`chunk migration
+   <migrate-chunks-sharded-cluster>`.
+   
+   Increasing the concurrency improves chunk migration performance, but
+   also increases the workload and disk IOPS usage on the the source
+   shard and the receiving shard.
+
+   Maximum value is 500.
+   
+   You should typically use half the total number of CPU cores as
+   threads. For example, if the total is 16 cores, set
+   ``chunkMigrationConcurrency`` to 8 threads (or fewer).
+
+   If ``chunkMigrationConcurrency`` is greater than ``1``, the
+   ``_secondaryThrottle`` configuration setting is ignored. The
+   ``_secondaryThrottle`` setting determines when the chunk migration
+   proceeds with the next document in the chunk. For details, see
+   :ref:`chunk-migration-replication`.
+
+   The following example sets ``chunkMigrationConcurrency`` to ``5``:
+
+   .. code-block:: bash
+
+      mongod --setParameter chunkMigrationConcurrency=5
+
+   During runtime, you can also set the parameter with the
+   :dbcommand:`setParameter` command:
+
+   .. code-block:: javascript
+
+      db.adminCommand( { setParameter: 1, chunkMigrationConcurrency: 5 } )
+
 .. parameter:: disableResumableRangeDeleter
 
    .. versionadded:: 4.4