Modify the graph interface to make possible select the type of operat…

…ion to perform (read or write)

lib/src/graph.rs

@@ -134,7 +134,19 @@ impl Graph {
     ///
     /// Transactions will not be automatically retried on any failure.
     pub async fn start_txn(&self) -> Result<Txn> {
-        self.impl_start_txn_on(self.config.db.clone()).await
+        self.impl_start_txn_on(self.config.db.clone(), Operation::Write)
+            .await
+    }
+
+    /// Starts a READ ONLY new transaction on the configured database.
+    /// All queries that needs to be run/executed within the transaction
+    /// should be executed using either [`Txn::run`] or [`Txn::execute`]
+    ///
+    /// Transactions will not be automatically retried on any failure.
+    #[cfg(feature = "unstable-bolt-protocol-impl-v2")]
+    pub async fn start_read_txn(&self) -> Result<Txn> {
+        self.impl_start_txn_on(self.config.db.clone(), Operation::Read)
+            .await
     }
 
     /// Starts a new transaction on the provided database.
@@ -143,11 +155,12 @@ impl Graph {
     ///
     /// Transactions will not be automatically retried on any failure.
     pub async fn start_txn_on(&self, db: impl Into<Database>) -> Result<Txn> {
-        self.impl_start_txn_on(Some(db.into())).await
+        self.impl_start_txn_on(Some(db.into()), Operation::Write)
+            .await
     }
 
-    async fn impl_start_txn_on(&self, db: Option<Database>) -> Result<Txn> {
-        let connection = self.pool.get(Some(Operation::Write)).await?;
+    async fn impl_start_txn_on(&self, db: Option<Database>, operation: Operation) -> Result<Txn> {
+        let connection = self.pool.get(Some(operation)).await?;
         Txn::new(db, self.config.fetch_size, connection).await
     }
 
@@ -163,6 +176,23 @@ impl Graph {
     ///
     /// use [`Graph::execute`] when you are interested in the result stream
     pub async fn run(&self, q: Query) -> Result<()> {
+        self.impl_run_on(self.config.db.clone(), q, Operation::Write)
+            .await
+    }
+
+    /// Runs a READ ONLY query on the configured database using a connection from the connection pool,
+    /// It doesn't return any [`DetachedRowStream`] as the `run` abstraction discards any stream.
+    ///
+    /// This operation retires the query on certain failures.
+    /// All errors with the `Transient` error class as well as a few other error classes are considered retryable.
+    /// This includes errors during a leader election or when the transaction resources on the server (memory, handles, ...) are exhausted.
+    /// Retries happen with an exponential backoff until a retry delay exceeds 60s, at which point the query fails with the last error as it would without any retry.
+    ///
+    /// Use [`Graph::run`] for cases where you just want a write operation
+    ///
+    /// use [`Graph::execute`] when you are interested in the result stream
+    #[cfg(feature = "unstable-bolt-protocol-impl-v2")]
+    pub async fn run_read(&self, q: Query) -> Result<()> {
         self.impl_run_on(self.config.db.clone(), q, Operation::Read)
             .await
     }
@@ -178,8 +208,13 @@ impl Graph {
     /// Use [`Graph::run`] for cases where you just want a write operation
     ///
     /// use [`Graph::execute`] when you are interested in the result stream
-    pub async fn run_on(&self, db: impl Into<Database>, q: Query) -> Result<()> {
-        self.impl_run_on(Some(db.into()), q, Operation::Read).await
+    pub async fn run_on(
+        &self,
+        db: impl Into<Database>,
+        q: Query,
+        operation: Operation,
+    ) -> Result<()> {
+        self.impl_run_on(Some(db.into()), q, operation).await
     }
 
     async fn impl_run_on(
@@ -205,7 +240,7 @@ impl Graph {
         .await
     }
 
-    /// Executes a query on the configured database and returns a [`DetachedRowStream`]
+    /// Executes a READ/WRITE query on the configured database and returns a [`DetachedRowStream`]
     ///
     /// This operation retires the query on certain failures.
     /// All errors with the `Transient` error class as well as a few other error classes are considered retryable.
@@ -216,17 +251,32 @@ impl Graph {
             .await
     }
 
-    /// Executes a query on the provided database and returns a [`DetachedRowStream`]
+    /// Executes a query READ on the configured database and returns a [`DetachedRowStream`]
     ///
     /// This operation retires the query on certain failures.
     /// All errors with the `Transient` error class as well as a few other error classes are considered retryable.
     /// This includes errors during a leader election or when the transaction resources on the server (memory, handles, ...) are exhausted.
     /// Retries happen with an exponential backoff until a retry delay exceeds 60s, at which point the query fails with the last error as it would without any retry.
-    pub async fn execute_on(&self, db: impl Into<Database>, q: Query) -> Result<DetachedRowStream> {
-        self.impl_execute_on(Some(db.into()), q, Operation::Write)
+    pub async fn execute_read(&self, q: Query) -> Result<DetachedRowStream> {
+        self.impl_execute_on(self.config.db.clone(), q, Operation::Read)
             .await
     }
 
+    /// Executes a query on the provided database and returns a [`DetachedRowStream`]
+    ///
+    /// This operation retires the query on certain failures.
+    /// All errors with the `Transient` error class as well as a few other error classes are considered retryable.
+    /// This includes errors during a leader election or when the transaction resources on the server (memory, handles, ...) are exhausted.
+    /// Retries happen with an exponential backoff until a retry delay exceeds 60s, at which point the query fails with the last error as it would without any retry.
+    pub async fn execute_on(
+        &self,
+        db: impl Into<Database>,
+        q: Query,
+        operation: Operation,
+    ) -> Result<DetachedRowStream> {
+        self.impl_execute_on(Some(db.into()), q, operation).await
+    }
+
     async fn impl_execute_on(
         &self,
         db: Option<Database>,

lib/src/routing/routed_connection_manager.rs

@@ -117,6 +117,7 @@ impl RoutedConnectionManager {
                 .load_balancing_strategy
                 .select_reader(available_servers.as_slice()),
         } {
+            debug!("requesting connection for server: {:?}", server);
             if let Some(pool) = self.registry.get_pool(&server) {
                 match pool.get().await {
                     Ok(connection) => return Ok(connection),