diff --git a/src/proxy/middle_relay.rs b/src/proxy/middle_relay.rs
index aebc628..01833fc 100644
--- a/src/proxy/middle_relay.rs
+++ b/src/proxy/middle_relay.rs
@@ -841,11 +841,23 @@ where
     let me_writer = tokio::spawn(async move {
         let mut writer = crypto_writer;
         let mut frame_buf = Vec::with_capacity(16 * 1024);
+        let shrink_threshold = d2c_flush_policy.frame_buf_shrink_threshold_bytes;
+
+        fn shrink_session_vec(buf: &mut Vec<u8>, threshold: usize) {
+            if buf.capacity() > threshold {
+                buf.clear();
+                buf.shrink_to(threshold);
+            } else {
+                buf.clear();
+            }
+        }
+
         loop {
             tokio::select! {
                 msg = me_rx_task.recv() => {
                     let Some(first) = msg else {
                         debug!(conn_id, "ME channel closed");
+                        shrink_session_vec(&mut frame_buf, shrink_threshold);
                         return Err(ProxyError::Proxy("ME connection lost".into()));
                     };
 
@@ -901,6 +913,7 @@ where
                                 batch_bytes,
                                 flush_duration_us,
                             );
+                            shrink_session_vec(&mut frame_buf, shrink_threshold);
                             return Ok(());
                         }
                     }
@@ -962,6 +975,7 @@ where
                                     batch_bytes,
                                     flush_duration_us,
                                 );
+                                shrink_session_vec(&mut frame_buf, shrink_threshold);
                                 return Ok(());
                             }
                         }
@@ -1027,6 +1041,7 @@ where
                                             batch_bytes,
                                             flush_duration_us,
                                         );
+                                        shrink_session_vec(&mut frame_buf, shrink_threshold);
                                         return Ok(());
                                     }
                                 }
@@ -1091,6 +1106,7 @@ where
                                                 batch_bytes,
                                                 flush_duration_us,
                                             );
+                                            shrink_session_vec(&mut frame_buf, shrink_threshold);
                                             return Ok(());
                                         }
                                     }
@@ -1098,6 +1114,7 @@ where
                             }
                             Ok(None) => {
                                 debug!(conn_id, "ME channel closed");
+                                shrink_session_vec(&mut frame_buf, shrink_threshold);
                                 return Err(ProxyError::Proxy("ME connection lost".into()));
                             }
                             Err(_) => {
@@ -1147,6 +1164,7 @@ where
                 }
                 _ = &mut stop_rx => {
                     debug!(conn_id, "ME writer stop signal");
+                    shrink_session_vec(&mut frame_buf, shrink_threshold);
                     return Ok(());
                 }
             }