Remove DB.Check(). Allow read-only Tx.Check().

This commit removes the DB.Check() function and instead makes the user decide
whether a transaction should be writable or read-only. Tx.Check() is not safe
to use concurrently on a read-only transaction, however, it significantly
improves the performance of it.

cmd/bolt/check.go

@@ -21,7 +21,12 @@ func Check(path string) {
 	defer db.Close()
 
 	// Perform consistency check.
-	if err := db.Check(); err != nil {
+	err = db.View(func(tx *bolt.Tx) error {
+		return tx.Check()
+	})
+
+	// Print out any errors that occur.
+	if err != nil {
 		if errors, ok := err.(bolt.ErrorList); ok {
 			for _, err := range errors {
 				println(err)

db.go

@@ -501,14 +501,6 @@ func (db *DB) Stats() Stats {
 	return db.stats
 }
 
-// Check performs several consistency checks on the database.
-// An error is returned if any inconsistency is found.
-func (db *DB) Check() error {
-	return db.Update(func(tx *Tx) error {
-		return tx.Check()
-	})
-}
-
 // This is for internal access to the raw data bytes from the C cursor, use
 // carefully, or not at all.
 func (db *DB) Info() *Info {

db_test.go

@@ -53,12 +53,12 @@ func TestOpen_Check(t *testing.T) {
 	withTempPath(func(path string) {
 		db, err := Open(path, 0666)
 		assert.NoError(t, err)
-		assert.NoError(t, db.Check())
+		assert.NoError(t, db.View(func(tx *Tx) error { return tx.Check() }))
 		db.Close()
 
 		db, err = Open(path, 0666)
 		assert.NoError(t, err)
-		assert.NoError(t, db.Check())
+		assert.NoError(t, db.View(func(tx *Tx) error { return tx.Check() }))
 		db.Close()
 	})
 }
@@ -463,7 +463,10 @@ func withOpenDB(fn func(*DB, string)) {
 
 // mustCheck runs a consistency check on the database and panics if any errors are found.
 func mustCheck(db *DB) {
-	if err := db.Check(); err != nil {
+	err := db.Update(func(tx *Tx) error {
+		return tx.Check()
+	})
+	if err != nil {
 		// Copy db off first.
 		var path = tempfile()
 		db.View(func(tx *Tx) error { return tx.CopyFile(path, 0600) })

tx.go

@@ -284,12 +284,14 @@ func (tx *Tx) CopyFile(path string, mode os.FileMode) error {
 }
 
 // Check performs several consistency checks on the database for this transaction.
-// An error is returned if any inconsistency is found or if executed on a read-only transaction.
+// An error is returned if any inconsistency is found.
+//
+// It can be safely run concurrently on a writable transaction. However, this
+// incurs a high cost for large databases and databases with a lot of subbuckets
+// because of caching. This overhead can be removed if running on a read-only
+// transaction, however, it is not safe to execute other writer transactions at
+// the same time.
 func (tx *Tx) Check() error {
-	if !tx.writable {
-		return ErrTxNotWritable
-	}
-
 	var errors ErrorList
 
 	// Check if any pages are double freed.
@@ -466,12 +468,10 @@ func (tx *Tx) forEachPage(pgid pgid, depth int, fn func(*page, int)) {
 }
 
 // Page returns page information for a given page number.
-// This is only available from writable transactions.
+// This is only safe for concurrent use when used by a writable transaction.
 func (tx *Tx) Page(id int) (*PageInfo, error) {
 	if tx.db == nil {
 		return nil, ErrTxClosed
-	} else if !tx.writable {
-		return nil, ErrTxNotWritable
 	} else if pgid(id) >= tx.meta.pgid {
 		return nil, nil
 	}