From 57ee90bb7314fd05b3387c07da75cd6594757fc1 Mon Sep 17 00:00:00 2001
From: Pavel Kalinnikov <pavel@cockroachlabs.com>
Date: Mon, 6 Feb 2023 20:32:47 +0000
Subject: [PATCH] kvserver: avoid duplicate loading in Store.Start

Release note: none
Epic: none
---
 pkg/kv/kvserver/kvstorage/init.go | 18 ++++++++++++++++++
 pkg/kv/kvserver/replica_init.go   |  9 +++++++--
 pkg/kv/kvserver/store.go          | 10 ++++++----
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/pkg/kv/kvserver/kvstorage/init.go b/pkg/kv/kvserver/kvstorage/init.go
index 00d76d452460..f0c1356102d2 100644
--- a/pkg/kv/kvserver/kvstorage/init.go
+++ b/pkg/kv/kvserver/kvstorage/init.go
@@ -17,6 +17,7 @@ import (
 
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/logstore"
+	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/stateloader"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/storage"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
@@ -312,6 +313,23 @@ func (r Replica) ID() storage.FullReplicaID {
 	}
 }
 
+// Load loads the state necessary to instantiate a replica in memory.
+func (r Replica) Load(ctx context.Context, eng storage.Reader) (LoadedReplicaState, error) {
+	ls := LoadedReplicaState{
+		ReplicaID: r.ReplicaID,
+		hardState: r.hardState,
+	}
+	sl := stateloader.Make(r.Desc.RangeID)
+	var err error
+	if ls.LastIndex, err = sl.LoadLastIndex(ctx, eng); err != nil {
+		return LoadedReplicaState{}, err
+	}
+	if ls.ReplState, err = sl.Load(ctx, eng, r.Desc); err != nil {
+		return LoadedReplicaState{}, err
+	}
+	return ls, nil
+}
+
 // A replicaMap organizes a set of Replicas with unique RangeIDs.
 type replicaMap map[roachpb.RangeID]Replica
 
diff --git a/pkg/kv/kvserver/replica_init.go b/pkg/kv/kvserver/replica_init.go
index 54fccc3d135a..2b355ad9ae17 100644
--- a/pkg/kv/kvserver/replica_init.go
+++ b/pkg/kv/kvserver/replica_init.go
@@ -54,12 +54,17 @@ func loadInitializedReplica(
 	if err != nil {
 		return nil, err
 	}
-	r := newUninitializedReplica(store, desc.RangeID, replicaID)
+	return newInitializedReplica(store, state)
+}
+
+// newInitializedReplica creates an initialized Replica from its loaded state.
+func newInitializedReplica(store *Store, loaded kvstorage.LoadedReplicaState) (*Replica, error) {
+	r := newUninitializedReplica(store, loaded.ReplState.Desc.RangeID, loaded.ReplicaID)
 	r.raftMu.Lock()
 	defer r.raftMu.Unlock()
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	if err := r.initRaftMuLockedReplicaMuLocked(state); err != nil {
+	if err := r.initRaftMuLockedReplicaMuLocked(loaded); err != nil {
 		return nil, err
 	}
 	return r, nil
diff --git a/pkg/kv/kvserver/store.go b/pkg/kv/kvserver/store.go
index c39bf59708a2..19de32acc82b 100644
--- a/pkg/kv/kvserver/store.go
+++ b/pkg/kv/kvserver/store.go
@@ -1861,10 +1861,12 @@ func (s *Store) Start(ctx context.Context, stopper *stop.Stopper) error {
 			// Uninitialized Replicas are not currently instantiated at store start.
 			continue
 		}
-		// TODO(sep-raft-log): construct the loaded Replica state directly in
-		// LoadAndReconcileReplicas, which loads and checks most of it already, then
-		// feed it to Replica creation, to avoid double-loading.
-		rep, err := loadInitializedReplica(ctx, s, repl.Desc, repl.ReplicaID)
+		// TODO(pavelkalinnikov): integrate into kvstorage.LoadAndReconcileReplicas.
+		state, err := repl.Load(ctx, s.Engine())
+		if err != nil {
+			return err
+		}
+		rep, err := newInitializedReplica(s, state)
 		if err != nil {
 			return err
 		}