Document execute_merges_on_single_replica_time_threshold setting

Задокументировал настройку execute_merges_on_single_replica_time_threshold.

docs/en/engines/table-engines/mergetree-family/replication.md

@@ -113,6 +113,8 @@ You can have any number of replicas of the same data. Yandex.Metrica uses double
 
 The system monitors data synchronicity on replicas and is able to recover after a failure. Failover is automatic (for small differences in data) or semi-automatic (when data differs too much, which may indicate a configuration error).
 
+You can use a special logic for performing merges (for more information, see the documentation for [execute_merges_on_single_replica_time_threshold](../../../operations/settings/settings.md#execute-merges-on-single-replica-time-threshold) setting). 
+
 ## Creating Replicated Tables {#creating-replicated-tables}
 
 The `Replicated` prefix is added to the table engine name. For example:`ReplicatedMergeTree`.

docs/en/operations/settings/settings.md

@@ -2410,7 +2410,6 @@ Result:
 {"number":"1"}
 {"number":"2"}
 ```
-
 =======
 ## allow_nullable_key {#allow-nullable-key}
 
@@ -2423,4 +2422,19 @@ Possible values:
 
 Default value: `0`.
 
+## execute_merges_on_single_replica_time_threshold {#execute-merges-on-single-replica-time-threshold}
+
+Enables special logic to perform merges on replicas.
+
+Possible values:
+
+-   Positive integer (in seconds).
+-   0 — Special merge logic is not executed.
+
+Default value: `0`.
+
+**Special logic to perform merges**
+
+Selects one replica to perform the merge on. Sets the time threshold from the start of the merge. Other replicas wait for the merge to finish, then download the result. If the time threshold passes and the selected replica does not perform merges, then the merge is performed manually.
+
 [Original article](https://clickhouse.tech/docs/en/operations/settings/settings/) <!-- hide -->