Use shard from query plan during execution

Lorak-mmk · wprzytula · Lorak-mmk · commit 7d17d2af146f · 2024-03-05T12:41:29.000+01:00
Co-authored-by: Wojciech Przytuła &lt;wojciech.przytula@scylladb.com&gt;
diff --git a/Cargo.lock.msrv b/Cargo.lock.msrv
diff --git a/scylla/src/transport/connection_pool.rs b/scylla/src/transport/connection_pool.rs
@@ -1,7 +1,7 @@
 #[cfg(feature = "cloud")]
 use crate::cloud::set_ssl_config_for_scylla_cloud_host;
 
-use crate::routing::{Shard, ShardCount, Sharder, Token};
+use crate::routing::{Shard, ShardCount, Sharder};
 use crate::transport::errors::QueryError;
 use crate::transport::{
     connection,
@@ -28,7 +28,7 @@ use std::time::Duration;
 
 use tokio::sync::{broadcast, mpsc, Notify};
 use tracing::instrument::WithSubscriber;
-use tracing::{debug, trace, warn};
+use tracing::{debug, error, trace, warn};
 
 /// The target size of a per-node connection pool.
 #[derive(Debug, Clone, Copy)]
@@ -235,22 +235,25 @@ impl NodeConnectionPool {
         .unwrap_or(None)
     }
 
-    pub(crate) fn connection_for_token(&self, token: Token) -> Result<Arc<Connection>, QueryError> {
-        trace!(token = token.value, "Selecting connection for token");
+    pub(crate) fn connection_for_shard(&self, shard: Shard) -> Result<Arc<Connection>, QueryError> {
+        trace!(shard = shard, "Selecting connection for shard");
         self.with_connections(|pool_conns| match pool_conns {
             PoolConnections::NotSharded(conns) => {
                 Self::choose_random_connection_from_slice(conns).unwrap()
             }
             PoolConnections::Sharded {
-                sharder,
                 connections,
+                sharder
             } => {
-                let shard: u16 = sharder
-                    .shard_of(token)
+                let shard = shard
                     .try_into()
-                    .expect("Shard number doesn't fit in u16");
-                trace!(shard = shard, "Selecting connection for token");
-                Self::connection_for_shard(shard, sharder.nr_shards, connections.as_slice())
+                    // It's safer to use 0 rather that panic here, as shards are returned by `LoadBalancingPolicy`
+                    // now, which can be implemented by a user in an arbitrary way.
+                    .unwrap_or_else(|_| {
+                        error!("The provided shard number: {} does not fit u16! Using 0 as the shard number.", shard);
+                        0
+                    });
+                Self::connection_for_shard_helper(shard, sharder.nr_shards, connections.as_slice())
             }
         })
     }
@@ -266,13 +269,13 @@ impl NodeConnectionPool {
                 connections,
             } => {
                 let shard: u16 = rand::thread_rng().gen_range(0..sharder.nr_shards.get());
-                Self::connection_for_shard(shard, sharder.nr_shards, connections.as_slice())
+                Self::connection_for_shard_helper(shard, sharder.nr_shards, connections.as_slice())
             }
         })
     }
 
     // Tries to get a connection to given shard, if it's broken returns any working connection
-    fn connection_for_shard(
+    fn connection_for_shard_helper(
         shard: u16,
         nr_shards: ShardCount,
         shard_conns: &[Vec<Arc<Connection>>],
diff --git a/scylla/src/transport/iterator.rs b/scylla/src/transport/iterator.rs
@@ -35,7 +35,7 @@ use crate::transport::connection::{Connection, NonErrorQueryResponse, QueryRespo
 use crate::transport::load_balancing::{self, RoutingInfo};
 use crate::transport::metrics::Metrics;
 use crate::transport::retry_policy::{QueryInfo, RetryDecision, RetrySession};
-use crate::transport::{Node, NodeRef};
+use crate::transport::NodeRef;
 use tracing::{trace, trace_span, warn, Instrument};
 use uuid::Uuid;
 
@@ -160,8 +160,6 @@ impl RowIterator {
         let worker_task = async move {
             let query_ref = &query;
 
-            let choose_connection = |node: Arc<Node>| async move { node.random_connection().await };
-
             let page_query = |connection: Arc<Connection>,
                               consistency: Consistency,
                               paging_state: Option<Bytes>| {
@@ -187,7 +185,6 @@ impl RowIterator {
 
             let worker = RowIteratorWorker {
                 sender: sender.into(),
-                choose_connection,
                 page_query,
                 statement_info: routing_info,
                 query_is_idempotent: query.config.is_idempotent,
@@ -259,13 +256,6 @@ impl RowIterator {
                 is_confirmed_lwt: config.prepared.is_confirmed_lwt(),
             };
 
-            let choose_connection = |node: Arc<Node>| async move {
-                match token {
-                    Some(token) => node.connection_for_token(token).await,
-                    None => node.random_connection().await,
-                }
-            };
-
             let page_query = |connection: Arc<Connection>,
                               consistency: Consistency,
                               paging_state: Option<Bytes>| async move {
@@ -311,7 +301,6 @@ impl RowIterator {
 
             let worker = RowIteratorWorker {
                 sender: sender.into(),
-                choose_connection,
                 page_query,
                 statement_info,
                 query_is_idempotent: config.prepared.config.is_idempotent,
@@ -496,13 +485,9 @@ type PageSendAttemptedProof = SendAttemptedProof<Result<ReceivedPage, QueryError
 
 // RowIteratorWorker works in the background to fetch pages
 // RowIterator receives them through a channel
-struct RowIteratorWorker<'a, ConnFunc, QueryFunc, SpanCreatorFunc> {
+struct RowIteratorWorker<'a, QueryFunc, SpanCreatorFunc> {
     sender: ProvingSender<Result<ReceivedPage, QueryError>>,
 
-    // Closure used to choose a connection from a node
-    // AsyncFn(Arc<Node>) -> Result<Arc<Connection>, QueryError>
-    choose_connection: ConnFunc,
-
     // Closure used to perform a single page query
     // AsyncFn(Arc<Connection>, Option<Bytes>) -> Result<QueryResponse, QueryError>
     page_query: QueryFunc,
@@ -524,11 +509,8 @@ struct RowIteratorWorker<'a, ConnFunc, QueryFunc, SpanCreatorFunc> {
     span_creator: SpanCreatorFunc,
 }
 
-impl<ConnFunc, ConnFut, QueryFunc, QueryFut, SpanCreator>
-    RowIteratorWorker<'_, ConnFunc, QueryFunc, SpanCreator>
+impl<QueryFunc, QueryFut, SpanCreator> RowIteratorWorker<'_, QueryFunc, SpanCreator>
 where
-    ConnFunc: Fn(Arc<Node>) -> ConnFut,
-    ConnFut: Future<Output = Result<Arc<Connection>, QueryError>>,
     QueryFunc: Fn(Arc<Connection>, Consistency, Option<Bytes>) -> QueryFut,
     QueryFut: Future<Output = Result<QueryResponse, QueryError>>,
     SpanCreator: Fn() -> RequestSpan,
@@ -546,12 +528,13 @@ where
 
         self.log_query_start();
 
-        'nodes_in_plan: for (node, _shard) in query_plan {
+        'nodes_in_plan: for (node, shard) in query_plan {
             let span =
                 trace_span!(parent: &self.parent_span, "Executing query", node = %node.address);
             // For each node in the plan choose a connection to use
             // This connection will be reused for same node retries to preserve paging cache on the shard
-            let connection: Arc<Connection> = match (self.choose_connection)(node.clone())
+            let connection: Arc<Connection> = match node
+                .connection_for_shard(shard)
                 .instrument(span.clone())
                 .await
             {
diff --git a/scylla/src/transport/node.rs b/scylla/src/transport/node.rs
@@ -3,7 +3,7 @@ use tracing::warn;
 use uuid::Uuid;
 
 /// Node represents a cluster node along with it's data and connections
-use crate::routing::{Sharder, Token};
+use crate::routing::{Shard, Sharder};
 use crate::transport::connection::Connection;
 use crate::transport::connection::VerifiedKeyspaceName;
 use crate::transport::connection_pool::{NodeConnectionPool, PoolConfig};
@@ -152,18 +152,13 @@ impl Node {
         self.pool.as_ref()?.sharder()
     }
 
-    /// Get connection which should be used to connect using given token
-    /// If this connection is broken get any random connection to this Node
-    pub(crate) async fn connection_for_token(
+    /// Get a connection targetting the given shard
+    /// If such connection is broken, get any random connection to this `Node`
+    pub(crate) async fn connection_for_shard(
         &self,
-        token: Token,
+        shard: Shard,
     ) -> Result<Arc<Connection>, QueryError> {
-        self.get_pool()?.connection_for_token(token)
-    }
-
-    /// Get random connection
-    pub(crate) async fn random_connection(&self) -> Result<Arc<Connection>, QueryError> {
-        self.get_pool()?.random_connection()
+        self.get_pool()?.connection_for_shard(shard)
     }
 
     pub fn is_down(&self) -> bool {
diff --git a/scylla/src/transport/session.rs b/scylla/src/transport/session.rs
@@ -655,7 +655,6 @@ impl Session {
                 statement_info,
                 &query.config,
                 execution_profile,
-                |node: Arc<Node>| async move { node.random_connection().await },
                 |connection: Arc<Connection>,
                  consistency: Consistency,
                  execution_profile: &ExecutionProfileInner| {
@@ -1024,12 +1023,6 @@ impl Session {
                 statement_info,
                 &prepared.config,
                 execution_profile,
-                |node: Arc<Node>| async move {
-                    match token {
-                        Some(token) => node.connection_for_token(token).await,
-                        None => node.random_connection().await,
-                    }
-                },
                 |connection: Arc<Connection>,
                  consistency: Consistency,
                  execution_profile: &ExecutionProfileInner| {
@@ -1236,14 +1229,6 @@ impl Session {
                 statement_info,
                 &batch.config,
                 execution_profile,
-                |node: Arc<Node>| async move {
-                    match first_value_token {
-                        Some(first_value_token) => {
-                            node.connection_for_token(first_value_token).await
-                        }
-                        None => node.random_connection().await,
-                    }
-                },
                 |connection: Arc<Connection>,
                  consistency: Consistency,
                  execution_profile: &ExecutionProfileInner| {
@@ -1507,28 +1492,23 @@ impl Session {
     }
 
     // This method allows to easily run a query using load balancing, retry policy etc.
-    // Requires some information about the query and two closures
-    // First closure is used to choose a connection
-    // - query will use node.random_connection()
-    // - execute will use node.connection_for_token()
-    // The second closure is used to do the query itself on a connection
+    // Requires some information about the query and a closure.
+    // The closure is used to do the query itself on a connection
     // - query will use connection.query()
     // - execute will use connection.execute()
     // If this query closure fails with some errors retry policy is used to perform retries
     // On success this query's result is returned
     // I tried to make this closures take a reference instead of an Arc but failed
     // maybe once async closures get stabilized this can be fixed
-    async fn run_query<'a, ConnFut, QueryFut, ResT>(
+    async fn run_query<'a, QueryFut, ResT>(
         &'a self,
         statement_info: RoutingInfo<'a>,
         statement_config: &'a StatementConfig,
         execution_profile: Arc<ExecutionProfileInner>,
-        choose_connection: impl Fn(Arc<Node>) -> ConnFut,
         do_query: impl Fn(Arc<Connection>, Consistency, &ExecutionProfileInner) -> QueryFut,
         request_span: &'a RequestSpan,
     ) -> Result<RunQueryResult<ResT>, QueryError>
     where
-        ConnFut: Future<Output = Result<Arc<Connection>, QueryError>>,
         QueryFut: Future<Output = Result<ResT, QueryError>>,
         ResT: AllowedRunQueryResTType,
     {
@@ -1602,7 +1582,6 @@ impl Session {
 
                         self.execute_query(
                             &shared_query_plan,
-                            &choose_connection,
                             &do_query,
                             &execution_profile,
                             ExecuteQueryContext {
@@ -1638,7 +1617,6 @@ impl Session {
                             });
                     self.execute_query(
                         query_plan,
-                        &choose_connection,
                         &do_query,
                         &execution_profile,
                         ExecuteQueryContext {
@@ -1684,16 +1662,14 @@ impl Session {
         result
     }
 
-    async fn execute_query<'a, ConnFut, QueryFut, ResT>(
+    async fn execute_query<'a, QueryFut, ResT>(
         &'a self,
         query_plan: impl Iterator<Item = (NodeRef<'a>, Shard)>,
-        choose_connection: impl Fn(Arc<Node>) -> ConnFut,
         do_query: impl Fn(Arc<Connection>, Consistency, &ExecutionProfileInner) -> QueryFut,
         execution_profile: &ExecutionProfileInner,
         mut context: ExecuteQueryContext<'a>,
     ) -> Option<Result<RunQueryResult<ResT>, QueryError>>
     where
-        ConnFut: Future<Output = Result<Arc<Connection>, QueryError>>,
         QueryFut: Future<Output = Result<ResT, QueryError>>,
         ResT: AllowedRunQueryResTType,
     {
@@ -1702,14 +1678,11 @@ impl Session {
             .consistency_set_on_statement
             .unwrap_or(execution_profile.consistency);
 
-        'nodes_in_plan: for (node, _shard) in query_plan {
+        'nodes_in_plan: for (node, shard) in query_plan {
             let span = trace_span!("Executing query", node = %node.address);
             'same_node_retries: loop {
                 trace!(parent: &span, "Execution started");
-                let connection: Arc<Connection> = match choose_connection(node.clone())
-                    .instrument(span.clone())
-                    .await
-                {
+                let connection = match node.connection_for_shard(shard).await {
                     Ok(connection) => connection,
                     Err(e) => {
                         trace!(
