Snapshot Sink sets MSRW name

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## v9.3.8 (unreleased)
 ### Implementation changes and bug fixes
 - [PR #2419](https://github.com/rqlite/rqlite/pull/2419): Improve MSRW Error structure.
+- [PR #2420](https://github.com/rqlite/rqlite/pull/2420): Snapshot Sink sets owner when taking MSRW.
 
 ## v9.3.7 (January 2nd 2026)
 ### Implementation changes and bug fixes

internal/rsync/multir_singlew.go

@@ -1,6 +1,7 @@
 package rsync
 
 import (
+	"fmt"
 	"sync"
 )
 
@@ -15,16 +16,16 @@ func (e *ErrMRSWConflict) Error() string {
 }
 
 // NewErrMRSWConflict creates a new ErrMRSWConflict with the given message.
-func NewErrMRSWConflict(msg string) error {
-	return &ErrMRSWConflict{msg: msg}
+func NewErrMRSWConflict(m string) error {
+	return &ErrMRSWConflict{msg: m}
 }
 
 // MultiRSW is a simple concurrency control mechanism that allows
 // multiple readers or a single writer to execute a critical section at a time.
 type MultiRSW struct {
-	writerActive bool
-	numReaders   int
-	mu           sync.Mutex
+	owner      string
+	numReaders int
+	mu         sync.Mutex
 }
 
 // NewMultiRSW creates a new MultiRSW instance.
@@ -36,8 +37,8 @@ func NewMultiRSW() *MultiRSW {
 func (r *MultiRSW) BeginRead() error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	if r.writerActive {
-		return NewErrMRSWConflict("MSRW conflict")
+	if r.owner != "" {
+		return NewErrMRSWConflict("MSRW conflict owner: " + r.owner)
 	}
 	r.numReaders++
 	return nil
@@ -54,13 +55,19 @@ func (r *MultiRSW) EndRead() {
 }
 
 // BeginWrite attempts to enter the critical section as a writer.
-func (r *MultiRSW) BeginWrite() error {
+func (r *MultiRSW) BeginWrite(owner string) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	if r.writerActive || r.numReaders > 0 {
-		return NewErrMRSWConflict("MSRW conflict")
+	if owner == "" {
+		panic("owner cannot be empty")
 	}
-	r.writerActive = true
+	if r.owner != "" {
+		return NewErrMRSWConflict("MSRW conflict owner: " + r.owner)
+	}
+	if r.numReaders > 0 {
+		return NewErrMRSWConflict(fmt.Sprintf("MSRW conflict %d readers active", r.numReaders))
+	}
+	r.owner = owner
 	return nil
 }
 
@@ -68,25 +75,28 @@ func (r *MultiRSW) BeginWrite() error {
 func (r *MultiRSW) EndWrite() {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	if !r.writerActive {
+	if r.owner == "" {
 		panic("write done received but no write is active")
 	}
-	r.writerActive = false
+	r.owner = ""
 }
 
 // UpgradeToWriter attempts to upgrade a read lock to a write lock. The
 // client must be the only reader in order to upgrade, and must already
 // be in a read lock.
-func (r *MultiRSW) UpgradeToWriter() error {
+func (r *MultiRSW) UpgradeToWriter(owner string) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	if r.writerActive || r.numReaders > 1 {
-		return NewErrMRSWConflict("MSRW conflict")
+	if r.owner != "" {
+		return NewErrMRSWConflict("MSRW conflict owner: " + r.owner)
+	}
+	if r.numReaders > 1 {
+		return NewErrMRSWConflict(fmt.Sprintf("MSRW conflict %d readers active", r.numReaders))
 	}
 	if r.numReaders == 0 {
 		panic("upgrade attempted with no readers")
 	}
-	r.writerActive = true
+	r.owner = owner
 	r.numReaders = 0
 	return nil
 }

internal/rsync/multir_singlew_test.go

@@ -14,20 +14,20 @@ func Test_MultiRSW(t *testing.T) {
 	r.EndRead()
 
 	// Test successful write lock
-	if err := r.BeginWrite(); err != nil {
+	if err := r.BeginWrite("owner1"); err != nil {
 		t.Fatalf("Failed to acquire write lock: %v", err)
 	}
 	r.EndWrite()
 
 	// Test that a write blocks other writers and readers.
-	err := r.BeginWrite()
+	err := r.BeginWrite("owner2")
 	if err != nil {
 		t.Fatalf("Failed to acquire write lock in goroutine: %v", err)
 	}
 	if err := r.BeginRead(); err == nil {
 		t.Fatalf("Expected error when reading during active write, got none")
 	}
-	if err := r.BeginWrite(); err == nil {
+	if err := r.BeginWrite("owner3"); err == nil {
 		t.Fatalf("Expected error when writing during active write, got none")
 	}
 	r.EndWrite()
@@ -37,7 +37,7 @@ func Test_MultiRSW(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to acquire read lock in goroutine: %v", err)
 	}
-	if err := r.BeginWrite(); err == nil {
+	if err := r.BeginWrite("owner4"); err == nil {
 		t.Fatalf("Expected error when writing during active read, got none")
 	}
 	r.EndRead()
@@ -61,7 +61,7 @@ func Test_MultiRSW_Upgrade(t *testing.T) {
 	if err := r.BeginRead(); err != nil {
 		t.Fatalf("Failed to acquire read lock: %v", err)
 	}
-	if err := r.UpgradeToWriter(); err != nil {
+	if err := r.UpgradeToWriter("owner11"); err != nil {
 		t.Fatalf("Failed to upgrade to write lock: %v", err)
 	}
 	r.EndWrite()
@@ -73,7 +73,7 @@ func Test_MultiRSW_Upgrade(t *testing.T) {
 	if err := r.BeginRead(); err != nil {
 		t.Fatalf("Failed to acquire read lock: %v", err)
 	}
-	if err := r.UpgradeToWriter(); err == nil {
+	if err := r.UpgradeToWriter("owner5"); err == nil {
 		t.Fatalf("Expected error when upgrading with multiple readers, got none")
 	}
 	r.EndRead()
@@ -83,19 +83,19 @@ func Test_MultiRSW_Upgrade(t *testing.T) {
 	if err := r.BeginRead(); err != nil {
 		t.Fatalf("Failed to acquire read lock: %v", err)
 	}
-	if err := r.UpgradeToWriter(); err != nil {
+	if err := r.UpgradeToWriter("owner6"); err != nil {
 		t.Fatalf("Failed to upgrade to write lock: %v", err)
 	}
-	if err := r.UpgradeToWriter(); err == nil {
+	if err := r.UpgradeToWriter("owner7"); err == nil {
 		t.Fatalf("Expected error when double-ugrading, got none")
 	}
 	r.EndWrite()
 
 	// Test that upgrades are blocked by other writers
-	if err := r.BeginWrite(); err != nil {
+	if err := r.BeginWrite("owner8"); err != nil {
 		t.Fatalf("Failed to acquire write lock: %v", err)
 	}
-	if err := r.UpgradeToWriter(); err == nil {
+	if err := r.UpgradeToWriter("owner9"); err == nil {
 		t.Fatalf("Expected error when upgrading with an active writer, got none")
 	}
 	r.EndWrite()

snapshot/store.go

@@ -171,7 +171,7 @@ func NewStore(dir string) (*Store, error) {
 // be a problem, since snapshots are taken infrequently in one at a time.
 func (s *Store) Create(version raft.SnapshotVersion, index, term uint64, configuration raft.Configuration,
 	configurationIndex uint64, trans raft.Transport) (retSink raft.SnapshotSink, retErr error) {
-	if err := s.mrsw.BeginWrite(); err != nil {
+	if err := s.mrsw.BeginWrite(fmt.Sprintf("snapshot-create-sink:%s", snapshotName(term, index))); err != nil {
 		stats.Add(snapshotCreateMRSWFail, 1)
 		return nil, err
 	}