feat: able to set read preference to flownode (#6696)

fix: correctly compare the opened follower regions in startup

Signed-off-by: luofucong <luofc@foxmail.com>

Cargo.lock

@@ -2747,6 +2747,7 @@ dependencies = [
 name = "common-session"
 version = "0.17.0"
 dependencies = [
+ "serde",
  "strum 0.27.1",
 ]
 

config/config.md

@@ -591,6 +591,7 @@
 | `flow.batching_mode.experimental_frontend_activity_timeout` | String | `60s` | Frontend activity timeout<br/>if frontend is down(not sending heartbeat) for more than frontend_activity_timeout,<br/>it will be removed from the list that flownode use to connect |
 | `flow.batching_mode.experimental_max_filter_num_per_query` | Integer | `20` | Maximum number of filters allowed in a single query |
 | `flow.batching_mode.experimental_time_window_merge_threshold` | Integer | `3` | Time window merge distance |
+| `flow.batching_mode.read_preference` | String | `Leader` | Read preference of the Frontend client. |
 | `grpc` | -- | -- | The gRPC server options. |
 | `grpc.bind_addr` | String | `127.0.0.1:6800` | The address to bind the gRPC server. |
 | `grpc.server_addr` | String | `127.0.0.1:6800` | The address advertised to the metasrv,<br/>and used for connections from outside the host |

config/flownode.example.toml

@@ -30,6 +30,8 @@ node_id = 14
 #+experimental_max_filter_num_per_query=20
 ## Time window merge distance
 #+experimental_time_window_merge_threshold=3
+## Read preference of the Frontend client.
+#+read_preference="Leader"
 
 ## The gRPC server options.
 [grpc]

src/common/session/Cargo.toml

@@ -8,4 +8,5 @@ license.workspace = true
 workspace = true
 
 [dependencies]
+serde.workspace = true
 strum.workspace = true

src/common/session/src/lib.rs

@@ -12,11 +12,14 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use serde::{Deserialize, Serialize};
 use strum::{AsRefStr, Display, EnumString};
 
 /// Defines the read preference for frontend route operations,
 /// determining whether to read from the region leader or follower.
-#[derive(Debug, Clone, Copy, Default, EnumString, Display, AsRefStr, PartialEq, Eq)]
+#[derive(
+    Debug, Clone, Copy, Default, EnumString, Display, AsRefStr, PartialEq, Serialize, Deserialize,
+)]
 pub enum ReadPreference {
     #[default]
     // Reads all operations from the region leader. This is the default mode.

src/datanode/src/datanode.rs

@@ -705,6 +705,7 @@ async fn open_all_regions(
             follower_regions.len()
         );
         let mut region_requests = Vec::with_capacity(follower_regions.len());
+        let num_regions = follower_regions.len();
         for (region_id, engine, store_path, options) in follower_regions {
             let table_dir = table_dir(&store_path, region_id.table_id());
             region_requests.push((

src/flow/src/batching_mode.rs

@@ -17,6 +17,7 @@
 use std::time::Duration;
 
 use serde::{Deserialize, Serialize};
+use session::ReadPreference;
 
 pub(crate) mod engine;
 pub(crate) mod frontend_client;
@@ -54,6 +55,8 @@ pub struct BatchingModeOptions {
     pub experimental_max_filter_num_per_query: usize,
     /// Time window merge distance
     pub experimental_time_window_merge_threshold: usize,
+    /// Read preference of the Frontend client.
+    pub read_preference: ReadPreference,
 }
 
 impl Default for BatchingModeOptions {
@@ -68,6 +71,7 @@ impl Default for BatchingModeOptions {
             experimental_frontend_activity_timeout: Duration::from_secs(60),
             experimental_max_filter_num_per_query: 20,
             experimental_time_window_merge_threshold: 3,
+            read_preference: Default::default(),
         }
     }
 }

src/flow/src/batching_mode/frontend_client.rs

@@ -36,6 +36,7 @@ use rand::rng;
 use rand::seq::SliceRandom;
 use servers::query_handler::grpc::GrpcQueryHandler;
 use session::context::{QueryContextBuilder, QueryContextRef};
+use session::hints::READ_PREFERENCE_HINT;
 use snafu::{OptionExt, ResultExt};
 
 use crate::batching_mode::BatchingModeOptions;
@@ -363,7 +364,10 @@ impl FrontendClient {
                     .handle_with_retry(
                         req.clone(),
                         batch_opts.experimental_grpc_max_retries,
-                        &[(QUERY_PARALLELISM_HINT, &query.parallelism.to_string())],
+                        &[
+                            (QUERY_PARALLELISM_HINT, &query.parallelism.to_string()),
+                            (READ_PREFERENCE_HINT, batch_opts.read_preference.as_ref()),
+                        ],
                     )
                     .await
                     .with_context(|_| InvalidRequestSnafu {

tests-integration/tests/http.rs

@@ -1269,6 +1269,7 @@ experimental_frontend_scan_timeout = "30s"
 experimental_frontend_activity_timeout = "1m"
 experimental_max_filter_num_per_query = 20
 experimental_time_window_merge_threshold = 3
+read_preference = "Leader"
 
 [logging]
 max_log_files = 720