Improve logging for connection cleanup (#428)

* initial commit

* fix

* fmt

src/server.rs

@@ -103,6 +103,48 @@ impl StreamInner {
     }
 }
 
+#[derive(Copy, Clone)]
+struct CleanupState {
+    /// If server connection requires DISCARD ALL before checkin because of set statement
+    needs_cleanup_set: bool,
+
+    /// If server connection requires DISCARD ALL before checkin because of prepare statement
+    needs_cleanup_prepare: bool,
+}
+
+impl CleanupState {
+    fn new() -> Self {
+        CleanupState {
+            needs_cleanup_set: false,
+            needs_cleanup_prepare: false,
+        }
+    }
+
+    fn needs_cleanup(&self) -> bool {
+        self.needs_cleanup_set || self.needs_cleanup_prepare
+    }
+
+    fn set_true(&mut self) {
+        self.needs_cleanup_set = true;
+        self.needs_cleanup_prepare = true;
+    }
+
+    fn reset(&mut self) {
+        self.needs_cleanup_set = false;
+        self.needs_cleanup_prepare = false;
+    }
+}
+
+impl std::fmt::Display for CleanupState {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "SET: {}, PREPARE: {}",
+            self.needs_cleanup_set, self.needs_cleanup_prepare
+        )
+    }
+}
+
 /// Server state.
 pub struct Server {
     /// Server host, e.g. localhost,
@@ -131,8 +173,8 @@ pub struct Server {
     /// Is the server broken? We'll remote it from the pool if so.
     bad: bool,
 
-    /// If server connection requires a DISCARD ALL before checkin
+    /// If server connection requires DISCARD ALL before checkin
-    needs_cleanup: bool,
+    cleanup_state: CleanupState,
 
     /// Mapping of clients and servers used for query cancellation.
     client_server_map: ClientServerMap,
@@ -630,7 +672,7 @@ impl Server {
                         in_transaction: false,
                         data_available: false,
                         bad: false,
-                        needs_cleanup: false,
+                        cleanup_state: CleanupState::new(),
                         client_server_map,
                         addr_set,
                         connected_at: chrono::offset::Utc::now().naive_utc(),
@@ -793,12 +835,12 @@ impl Server {
                                     // This will reduce amount of discard statements sent
                                     if !self.in_transaction {
                                         debug!("Server connection marked for clean up");
-                                        self.needs_cleanup = true;
+                                        self.cleanup_state.needs_cleanup_set = true;
                                     }
                                 }
                                 "PREPARE\0" => {
                                     debug!("Server connection marked for clean up");
-                                    self.needs_cleanup = true;
+                                    self.cleanup_state.needs_cleanup_prepare = true;
                                 }
                                 _ => (),
                             }
@@ -960,11 +1002,11 @@ impl Server {
         // to avoid leaking state between clients. For performance reasons we only
         // send `DISCARD ALL` if we think the session is altered instead of just sending
         // it before each checkin.
-        if self.needs_cleanup {
+        if self.cleanup_state.needs_cleanup() {
-            warn!("Server returned with session state altered, discarding state");
+            warn!("Server returned with session state altered, discarding state ({}) for application {}", self.cleanup_state, self.application_name);
             self.query("DISCARD ALL").await?;
             self.query("RESET ROLE").await?;
-            self.needs_cleanup = false;
+            self.cleanup_state.reset();
         }
 
         Ok(())
@@ -976,12 +1018,12 @@ impl Server {
             self.application_name = name.to_string();
             // We don't want `SET application_name` to mark the server connection
             // as needing cleanup
-            let needs_cleanup_before = self.needs_cleanup;
+            let needs_cleanup_before = self.cleanup_state;
 
             let result = Ok(self
                 .query(&format!("SET application_name = '{}'", name))
                 .await?);
-            self.needs_cleanup = needs_cleanup_before;
+            self.cleanup_state = needs_cleanup_before;
             result
         } else {
             Ok(())
@@ -1006,7 +1048,7 @@ impl Server {
 
     // Marks a connection as needing DISCARD ALL at checkin
     pub fn mark_dirty(&mut self) {
-        self.needs_cleanup = true;
+        self.cleanup_state.set_true();
     }
 
     pub fn mirror_send(&mut self, bytes: &BytesMut) {