RUST-2448 Update client backpressure docs (#1730)

Author: isabelatkinson

driver/src/client.rs

@@ -120,10 +120,10 @@ const DEFAULT_SERVER_SELECTION_TIMEOUT: Duration = Duration::from_secs(30);
 /// details.
 ///
 /// ## Overload Retry Behavior
-/// All operations executed by a `Client` may retry if the selected server is overloaded. For
-/// details on server load-shedding, see the documentation for
-/// [Intelligent Workload Management](https://www.mongodb.com/docs/atlas/intelligent-workload-management/)
-/// and [Overload Errors](https://www.mongodb.com/docs/atlas/overload-errors).
+/// All operations executed by a `Client` may retry if the selected server is overloaded. An
+/// overload error is indicated by the
+/// [`SYSTEM_OVERLOADED_ERROR`](crate::error::SYSTEM_OVERLOADED_ERROR) error label. This behavior is
+/// functional with MongoDB Atlas server version 9.0 and above.
 ///
 /// The following options can be configured to customize this behavior:
 /// - Set [`ClientOptions::retry_reads`] to false to disable retrying all reads. Note that this will

driver/src/client/options.rs

@@ -689,11 +689,15 @@ pub struct ClientOptions {
 
     /// The maximum number of retries to perform when overload errors are encountered. Defaults to
     /// 2.
+    ///
+    /// This option only has an effect with MongoDB Atlas server version 9.0 and above.
     pub max_adaptive_retries: Option<u32>,
 
     /// Whether to enable overload retargeting when overload errors are encountered. When overload
     /// retargeting is enabled, the server on which an overload error occurs is deprioritized
     /// when selecting a server for a retry attempt. Defaults to false.
+    ///
+    /// This option only has an effect with MongoDB Atlas server version 9.0 and above.
     pub enable_overload_retargeting: Option<bool>,
 
     /// Information from the SRV URI that generated these client options, if applicable.
@@ -1088,11 +1092,15 @@ pub struct ConnectionString {
 
     /// The maximum number of retries to perform when overload errors are encountered. Defaults to
     /// 2.
+    ///
+    /// This option only has an effect with MongoDB Atlas server version 9.0 and above.
     pub max_adaptive_retries: Option<u32>,
 
     /// Whether to enable overload retargeting when overload errors are encountered. When overload
     /// retargeting is enabled, the server on which an overload error occurs is deprioritized
     /// when selecting a server for a retry attempt. Defaults to false.
+    ///
+    /// This option only has an effect with MongoDB Atlas server version 9.0 and above.
     pub enable_overload_retargeting: Option<bool>,
 
     #[serde(serialize_with = "serde_util::serialize_duration_option_as_int_millis")]