Add BypassDirLock option (#1243)

Fixes #988
Based on #1046

This PR adds `BypassDirLock` option which allows badger to work without
acquiring a lock on the data directory. This option could lead to data
corruption if used with multiple badger instances trying to write to
the same badger directory.

Co-authored-by: Ehsan Noureddin Moosa <[email protected]>
(cherry picked from commit 1bcbefc)

Author: Ibrahim Jarif

db.go

@@ -217,34 +217,36 @@ func Open(opt Options) (db *DB, err error) {
 			}
 		}
 	}
-	absDir, err := filepath.Abs(opt.Dir)
-	if err != nil {
-		return nil, err
-	}
-	absValueDir, err := filepath.Abs(opt.ValueDir)
-	if err != nil {
-		return nil, err
-	}
 	var dirLockGuard, valueDirLockGuard *directoryLockGuard
-	dirLockGuard, err = acquireDirectoryLock(opt.Dir, lockFile, opt.ReadOnly)
-	if err != nil {
-		return nil, err
-	}
-	defer func() {
-		if dirLockGuard != nil {
-			_ = dirLockGuard.release()
+	if !opt.BypassLockGuard {
+		absDir, err := filepath.Abs(opt.Dir)
+		if err != nil {
+			return nil, err
 		}
-	}()
-	if absValueDir != absDir {
-		valueDirLockGuard, err = acquireDirectoryLock(opt.ValueDir, lockFile, opt.ReadOnly)
+		absValueDir, err := filepath.Abs(opt.ValueDir)
+		if err != nil {
+			return nil, err
+		}
+		dirLockGuard, err = acquireDirectoryLock(opt.Dir, lockFile, opt.ReadOnly)
 		if err != nil {
 			return nil, err
 		}
 		defer func() {
-			if valueDirLockGuard != nil {
-				_ = valueDirLockGuard.release()
+			if dirLockGuard != nil {
+				_ = dirLockGuard.release()
 			}
 		}()
+		if absValueDir != absDir {
+			valueDirLockGuard, err = acquireDirectoryLock(opt.ValueDir, lockFile, opt.ReadOnly)
+			if err != nil {
+				return nil, err
+			}
+			defer func() {
+				if valueDirLockGuard != nil {
+					_ = valueDirLockGuard.release()
+				}
+			}()
+		}
 	}
 	if !(opt.ValueLogFileSize <= 2<<30 && opt.ValueLogFileSize >= 1<<20) {
 		return nil, ErrValueLogSize

options.go

@@ -67,6 +67,11 @@ type Options struct {
 	// When set, checksum will be validated for each entry read from the value log file.
 	VerifyValueChecksum bool
 
+	// BypassLockGaurd will bypass the lock guard on badger. Bypassing lock
+	// guard can cause data corruption if multiple badger instances are using
+	// the same directory. Use this options with caution.
+	BypassLockGuard bool
+
 	// Transaction start and commit timestamps are managed by end-user.
 	// This is only useful for databases built on top of Badger (like Dgraph).
 	// Not recommended for most users.
@@ -400,3 +405,16 @@ func (opt Options) WithVerifyValueChecksum(val bool) Options {
 	opt.VerifyValueChecksum = val
 	return opt
 }
+
+// WithBypassLockGuard returns a new Options value with BypassLockGuard
+// set to the given value.
+//
+// When BypassLockGuard option is set, badger will not acquire a lock on the
+// directory. This could lead to data corruption if multiple badger instances
+// write to the same data directory. Use this option with caution.
+//
+// The default value of BypassLockGuard is false.
+func (opt Options) WithBypassLockGuard(b bool) Options {
+	opt.BypassLockGuard = b
+	return opt
+}