SERVER-75082 Make balancer migrations throttling configurable

2 files changed, 15 insertions, 9 deletions

diff --git a/src/mongo/db/s/balancer/balancer.cpp b/src/mongo/db/s/balancer/balancer.cpp
index 36f53d7a5fc..3a49362f62e 100644
--- a/src/mongo/db/s/balancer/balancer.cpp
+++ b/src/mongo/db/s/balancer/balancer.cpp
@@ -80,12 +80,6 @@ MONGO_FAIL_POINT_DEFINE(overrideBalanceRoundInterval);
 
 const Milliseconds kBalanceRoundDefaultInterval(10 * 1000);
 
-// Sleep between balancer rounds in the case where the last round found some chunks which needed to
-// be balanced. This value should be set sufficiently low so that imbalanced clusters will quickly
-// reach balanced state, but setting it too low may cause CRUD operations to start failing due to
-// not being able to establish a stable shard version.
-const Milliseconds kBalancerMigrationsThrottling(1 * 1000);
-
 /**
  * Balancer status response
  */
@@ -819,7 +813,8 @@ void Balancer::_mainThread() {
                     _sleepFor(opCtx.get(),
                               forcedBalancerRoundInterval
                                   ? *forcedBalancerRoundInterval - timeSinceLastMigration
-                                  : kBalancerMigrationsThrottling - timeSinceLastMigration);
+                                  : Milliseconds(balancerMigrationsThrottlingMs.load()) -
+                                      timeSinceLastMigration);
 
                     _balancedLastTime =
                         _moveChunks(opCtx.get(), chunksToRebalance, chunksToDefragment);
@@ -835,8 +830,8 @@ void Balancer::_mainThread() {
                         .ignore();
 
                     LOGV2_DEBUG(6679500, 1, "End balancing round");
-                    // Migration throttling of kBalancerMigrationsThrottling will be applied before
-                    // the next call to _moveChunks, so don't sleep here.
+                    // Migration throttling of `balancerMigrationsThrottlingMs` will be applied
+                    // before the next call to _moveChunks, so don't sleep here.
                     _endRound(opCtx.get(), Milliseconds(0));
                 }
             }
diff --git a/src/mongo/db/s/sharding_config_server_parameters.idl b/src/mongo/db/s/sharding_config_server_parameters.idl
index 1c6402a10db..89b0bea726a 100644
--- a/src/mongo/db/s/sharding_config_server_parameters.idl
+++ b/src/mongo/db/s/sharding_config_server_parameters.idl
@@ -47,6 +47,17 @@ server_parameters:
           gte: 0
         default: 1000
 
+    balancerMigrationsThrottlingMs:
+        # Sleep between balancer rounds in the case where the last round found some chunks which needed to
+        # be balanced. This value should be set sufficiently low so that imbalanced clusters will quickly
+        # reach balanced state, but setting it too low may cause CRUD operations to start failing due to
+        # not being able to establish a stable shard version.
+        description: The minimum amount of time between two consecutive balancing rounds
+        set_at: [startup, runtime]
+        cpp_vartype: AtomicWord<int32_t>
+        cpp_varname: balancerMigrationsThrottlingMs
+        default: 1000 # 1 sec
+
     balancerChunksSelectionTimeoutMs:
         description: >-
             Maximum time in milliseconds the balancer will spend deciding which ranges to move in