DOCSP-25925-migrationConcurrency (BACKPORT) (#2495)

* DOCSP-25925-migrationConcurrency (#2144)

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

* DOCSP-25925-migrationConcurrency

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

* DOCSP-25927 Backport: Document new server parameter: migrationConcurrency

---------

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

Author: 2 people

source/reference/parameters.txt

@@ -3014,6 +3014,40 @@ Sharding Parameters
 
       db.adminCommand( { setParameter: 1, chunkDefragmentationThrottlingMS: 10 } )
 
+.. parameter:: chunkMigrationConcurrency
+
+   *Available starting in MongoDB 6.0.5 (and 5.0.16)*
+
+   *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 fewer than 32 threads
+   unless you are using NVMe (Non-Volatile Memory Express) disks.
+
+   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