Read concurrency

.changeset/change_chain_manager_mutex_to_rwmutex_to_enable_parallel_reads.md

@@ -0,0 +1,5 @@
+---
+default: patch
+---
+
+# Change Chain Manager Mutex to RWMutex to enable parallel reads

chain/db.go

@@ -65,6 +65,14 @@ type DB interface {
 	CreateBucket(name []byte) (DBBucket, error)
 	Flush() error
 	Cancel()
+
+	// View calls fn with a read-only DB. Implementations must guarantee
+	// that the DB passed to fn observes a consistent snapshot for the
+	// duration of fn, and that fn may run concurrently with other View
+	// calls. Buckets obtained via the DB inside fn must not be used
+	// after fn returns. Writes via the DB inside fn are not durable
+	// and may panic.
+	View(fn func(DB) error) error
 }
 
 // A DBBucket is a set of key-value pairs.
@@ -105,6 +113,12 @@ func (db *MemDB) Flush() error {
 	return nil
 }
 
+// View implements DB. MemDB has no MVCC; callers must ensure that no writes
+// occur concurrently with the View call.
+func (db *MemDB) View(fn func(DB) error) error {
+	return fn(db)
+}
+
 // Cancel implements DB.
 func (db *MemDB) Cancel() {
 	for k := range db.puts {
@@ -336,6 +350,12 @@ func (db *CacheDB) Cancel() {
 	db.db.Cancel()
 }
 
+// View implements DB. CacheDB has no MVCC; callers must ensure that no writes
+// occur concurrently with the View call.
+func (db *CacheDB) View(fn func(DB) error) error {
+	return fn(db)
+}
+
 // NewCacheDB returns a new CacheDB that wraps the given DB.
 func NewCacheDB(db DB) DB {
 	return &CacheDB{
@@ -948,6 +968,16 @@ func (db *DBStore) Flush() error {
 	return err
 }
 
+// View implements Store. It calls fn with a read-only Store backed by a
+// consistent snapshot of the underlying DB. The Store passed to fn must not be
+// used after fn returns. Writes performed via the Store will fail.
+func (db *DBStore) View(fn func(Store)) error {
+	return db.db.View(func(rdb DB) error {
+		fn(&DBStore{db: rdb, n: db.n})
+		return nil
+	})
+}
+
 // NewDBStore creates a new DBStore using the provided database. The tip state
 // is also returned. The DB will be automatically migrated if necessary. The
 // provided logger may be nil.