Fix: Load mebmership since last_applied, not last_membership.index on startup

Modify `StorageHelper::last_membership_in_log()` to scan the log
starting from the last applied index rather than the index of the last
applied membership log. This change reduces unnecessary I/O operations
during startup, previously caused by scanning from an incorrect starting
point.

Author: drmingdrmer

openraft/src/storage/helper.rs

@@ -192,11 +192,9 @@ where
     ///
     /// Thus a raft node will only need to store at most two recent membership logs.
     pub async fn get_membership(&mut self) -> Result<MembershipState<C::NodeId, C::Node>, StorageError<C::NodeId>> {
-        let (_, sm_mem) = self.state_machine.applied_state().await?;
+        let (last_applied, sm_mem) = self.state_machine.applied_state().await?;
 
-        let sm_mem_next_index = sm_mem.log_id().next_index();
-
-        let log_mem = self.last_membership_in_log(sm_mem_next_index).await?;
+        let log_mem = self.last_membership_in_log(last_applied.next_index()).await?;
         tracing::debug!(membership_in_sm=?sm_mem, membership_in_log=?log_mem, "RaftStorage::get_membership");
 
         // There 2 membership configs in logs.
@@ -234,6 +232,9 @@ where
         let st = self.log_store.get_log_state().await?;
 
         let mut end = st.last_log_id.next_index();
+
+        tracing::info!("load membership from log: [{}..{})", since_index, end);
+
         let start = std::cmp::max(st.last_purged_log_id.next_index(), since_index);
         let step = 64;
 

openraft/src/testing/suite.rs

@@ -85,7 +85,10 @@ where
         run_fut(run_test(builder, Self::last_membership_in_log_multi_step))?;
         run_fut(run_test(builder, Self::get_membership_initial))?;
         run_fut(run_test(builder, Self::get_membership_from_log_and_empty_sm))?;
-        run_fut(run_test(builder, Self::get_membership_from_log_and_sm))?;
+        run_fut(run_test(builder, Self::get_membership_from_empty_log_and_sm))?;
+        run_fut(run_test(builder, Self::get_membership_from_log_le_sm_last_applied))?;
+        run_fut(run_test(builder, Self::get_membership_from_log_gt_sm_last_applied_1))?;
+        run_fut(run_test(builder, Self::get_membership_from_log_gt_sm_last_applied_2))?;
         run_fut(run_test(builder, Self::get_initial_state_without_init))?;
         run_fut(run_test(builder, Self::get_initial_state_membership_from_log_and_sm))?;
         run_fut(run_test(builder, Self::get_initial_state_with_state))?;
@@ -259,7 +262,10 @@ where
         Ok(())
     }
 
-    pub async fn get_membership_from_log_and_sm(mut store: LS, mut sm: SM) -> Result<(), StorageError<C::NodeId>> {
+    pub async fn get_membership_from_empty_log_and_sm(
+        mut store: LS,
+        mut sm: SM,
+    ) -> Result<(), StorageError<C::NodeId>> {
         tracing::info!("--- no log, read membership from state machine");
         {
             apply(&mut sm, [
@@ -279,10 +285,31 @@ where
                 mem_state.effective().membership(),
             );
         }
+        Ok(())
+    }
 
+    pub async fn get_membership_from_log_le_sm_last_applied(
+        mut store: LS,
+        mut sm: SM,
+    ) -> Result<(), StorageError<C::NodeId>> {
         tracing::info!("--- membership presents in log, but smaller than last_applied, read from state machine");
         {
-            append(&mut store, [membership_ent_0::<C>(1, 1, btreeset! {1,2,3})]).await?;
+            apply(&mut sm, [
+                blank_ent_0::<C>(1, 1),
+                membership_ent_0::<C>(1, 2, btreeset! {3,4,5}),
+                blank_ent_0::<C>(1, 3),
+                blank_ent_0::<C>(1, 4),
+            ])
+            .await?;
+
+            // Intentionally append a membership entry that does not match the state machine,
+            // in order to see which membership is loaded.
+            append(&mut store, [
+                blank_ent_0::<C>(1, 1),
+                blank_ent_0::<C>(1, 2),
+                membership_ent_0::<C>(1, 3, btreeset! {1,2,3}),
+            ])
+            .await?;
 
             let mem_state = StorageHelper::new(&mut store, &mut sm).get_membership().await?;
 
@@ -295,10 +322,23 @@ where
                 mem_state.effective().membership(),
             );
         }
+        Ok(())
+    }
 
+    pub async fn get_membership_from_log_gt_sm_last_applied_1(
+        mut store: LS,
+        mut sm: SM,
+    ) -> Result<(), StorageError<C::NodeId>> {
         tracing::info!("--- membership presents in log and > sm.last_applied, read from log");
         {
+            apply(&mut sm, [
+                blank_ent_0::<C>(1, 1),
+                membership_ent_0::<C>(1, 2, btreeset! {3,4,5}),
+            ])
+            .await?;
+
             append(&mut store, [
+                membership_ent_0::<C>(1, 1, btreeset! {1,2,3}),
                 blank_ent_0::<C>(1, 2),
                 membership_ent_0::<C>(1, 3, btreeset! {7,8,9}),
             ])
@@ -315,10 +355,25 @@ where
                 mem_state.effective().membership(),
             );
         }
+        Ok(())
+    }
 
+    pub async fn get_membership_from_log_gt_sm_last_applied_2(
+        mut store: LS,
+        mut sm: SM,
+    ) -> Result<(), StorageError<C::NodeId>> {
         tracing::info!("--- two membership present in log and > sm.last_applied, read 2 from log");
         {
+            apply(&mut sm, [
+                blank_ent_0::<C>(1, 1),
+                membership_ent_0::<C>(1, 2, btreeset! {3,4,5}),
+            ])
+            .await?;
+
             append(&mut store, [
+                membership_ent_0::<C>(1, 1, btreeset! {1,2,3}),
+                blank_ent_0::<C>(1, 2),
+                membership_ent_0::<C>(1, 3, btreeset! {7,8,9}),
                 blank_ent_0::<C>(1, 4),
                 membership_ent_0::<C>(1, 5, btreeset! {10,11}),
             ])