feat(core): Add route hint, make load balancer easier to route queries (

#469)

* add RouteHintGenerator

* add in_active_transaction

* reset route hint

* chore: rename to route hint

* handle the route hint from query response

core/src/client.rs

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 use std::collections::BTreeMap;
+use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -41,6 +42,8 @@ const HEADER_QUERY_ID: &str = "X-DATABEND-QUERY-ID";
 const HEADER_TENANT: &str = "X-DATABEND-TENANT";
 const HEADER_WAREHOUSE: &str = "X-DATABEND-WAREHOUSE";
 const HEADER_STAGE_NAME: &str = "X-DATABEND-STAGE-NAME";
+const HEADER_ROUTE_HINT: &str = "X-DATABEND-ROUTE-HINT";
+const TXN_STATE_ACTIVE: &str = "Active";
 
 static VERSION: Lazy<String> = Lazy::new(|| {
     let version = option_env!("CARGO_PKG_VERSION").unwrap_or("unknown");
@@ -61,6 +64,7 @@ pub struct APIClient {
     tenant: Option<String>,
     warehouse: Arc<Mutex<Option<String>>>,
     session_state: Arc<Mutex<SessionState>>,
+    route_hint: Arc<RouteHintGenerator>,
 
     wait_time_secs: Option<i64>,
     max_rows_in_buffer: Option<i64>,
@@ -241,6 +245,15 @@ impl APIClient {
         guard.role.clone()
     }
 
+    async fn in_active_transaction(&self) -> bool {
+        let guard = self.session_state.lock().await;
+        guard
+            .txn_state
+            .as_ref()
+            .map(|s| s.eq_ignore_ascii_case(TXN_STATE_ACTIVE))
+            .unwrap_or(false)
+    }
+
     pub fn username(&self) -> String {
         self.auth.username()
     }
@@ -280,6 +293,9 @@ impl APIClient {
 
     pub async fn start_query(&self, sql: &str) -> Result<QueryResponse> {
         info!("start query: {}", sql);
+        if !self.in_active_transaction().await {
+            self.route_hint.next();
+        }
         let session_state = self.session_state().await;
         let req = QueryRequest::new(sql)
             .with_pagination(self.make_pagination())
@@ -308,13 +324,16 @@ impl APIClient {
             )));
         }
 
-        let resp: QueryResponse = resp.json().await?;
-        self.handle_session(&resp.session).await;
-        if let Some(err) = resp.error {
+        if let Some(route_hint) = resp.headers().get(HEADER_ROUTE_HINT) {
+            self.route_hint.set(route_hint.to_str().unwrap_or_default());
+        }
+        let result: QueryResponse = resp.json().await?;
+        self.handle_session(&result.session).await;
+        if let Some(err) = result.error {
             return Err(Error::InvalidResponse(err));
         }
-        self.handle_warnings(&resp);
-        Ok(resp)
+        self.handle_warnings(&result);
+        Ok(result)
     }
 
     pub async fn query_page(&self, query_id: &str, next_uri: &str) -> Result<QueryResponse> {
@@ -434,6 +453,8 @@ impl APIClient {
         if let Some(warehouse) = &*warehouse {
             headers.insert(HEADER_WAREHOUSE, warehouse.parse()?);
         }
+        let route_hint = self.route_hint.current();
+        headers.insert(HEADER_ROUTE_HINT, route_hint.parse()?);
         headers.insert(HEADER_QUERY_ID, query_id.parse()?);
         Ok(headers)
     }
@@ -588,10 +609,46 @@ impl Default for APIClient {
             page_request_timeout: Duration::from_secs(30),
             tls_ca_file: None,
             presign: PresignMode::Auto,
+            route_hint: Arc::new(RouteHintGenerator::new()),
         }
     }
 }
 
+struct RouteHintGenerator {
+    nonce: AtomicU64,
+    current: std::sync::Mutex<String>,
+}
+
+impl RouteHintGenerator {
+    fn new() -> Self {
+        let gen = Self {
+            nonce: AtomicU64::new(0),
+            current: std::sync::Mutex::new("".to_string()),
+        };
+        gen.next();
+        gen
+    }
+
+    fn current(&self) -> String {
+        let guard = self.current.lock().unwrap();
+        guard.clone()
+    }
+
+    fn set(&self, hint: &str) {
+        let mut guard = self.current.lock().unwrap();
+        *guard = hint.to_string();
+    }
+
+    fn next(&self) -> String {
+        let nonce = self.nonce.fetch_add(1, Ordering::AcqRel);
+        let uuid = uuid::Uuid::new_v4();
+        let current = format!("rh:{}:{:06}", uuid, nonce);
+        let mut guard = self.current.lock().unwrap();
+        *guard = current.clone();
+        current
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;