feat: add application_name_add_host setting

pgdog-config/src/general.rs

@@ -730,6 +730,13 @@ pub struct General {
     /// https://docs.pgdog.dev/configuration/pgdog.toml/general/#cutover_save_config
     #[serde(default)]
     pub cutover_save_config: bool,
+
+    /// Append the client host address and port to the application_name set on connection start.
+    /// This helps identify the source of queries in pg_stat_activity.
+    ///
+    /// _Default:_ `false`
+    #[serde(default)]
+    pub application_name_add_host: bool,
 }
 
 impl Default for General {
@@ -827,6 +834,7 @@ impl Default for General {
             cutover_timeout: Self::cutover_timeout(),
             cutover_timeout_action: Self::cutover_timeout_action(),
             cutover_save_config: bool::default(),
+            application_name_add_host: bool::default(),
             unique_id_function: Self::unique_id_function(),
         }
     }

pgdog/src/frontend/client/query_engine/connect.rs

@@ -44,6 +44,24 @@ impl QueryEngine {
                 let begin_stmt = self.begin_stmt.take();
 
                 // We may need to sync params with the server and that reads from the socket.
+                // If application_name_add_host is enabled, append client address to application_name.
+                // This matches PgBouncer behavior: only applied at connection start, not on SET.
+                if crate::config::config()
+                    .config
+                    .general
+                    .application_name_add_host
+                {
+                    if let Some(addr) = *context.stream.peer_addr() {
+                        let base = context
+                            .params
+                            .get_default("application_name", "PgDog")
+                            .to_owned();
+                        let with_host = format!("{} ({})", base, addr);
+                        context
+                            .params
+                            .insert("application_name", with_host.as_str());
+                    }
+                }
                 timeout(
                     query_timeout,
                     self.backend.link_client(