fix #274. open a new fd for replay

Since we have to seek to the right location of the file, we cannot use
the same fd or dup it. File descriptors share the same file location.

src/wal/log.go

@@ -12,7 +12,6 @@ import (
 	"protocol"
 	"strconv"
 	"strings"
-	"syscall"
 )
 
 type log struct {
@@ -111,7 +110,6 @@ func (self *log) recover() error {
 
 	self.state.RequestsSinceLastBookmark = 0
 	self.state.RequestsSinceLastIndex = 0
-	self.state.setFileOffset(self.state.FileOffset)
 
 	logger.Debug("Recovering from previous state from file offset: %d", self.state.FileOffset)
 
@@ -227,11 +225,7 @@ func (self *log) appendRequest(request *protocol.Request, shardId uint32) (uint3
 }
 
 func (self *log) dupLogFile() (*os.File, error) {
-	fd, err := syscall.Dup(int(self.file.Fd()))
-	if err != nil {
-		return nil, err
-	}
-	return os.NewFile(uintptr(fd), self.file.Name()), nil
+	return os.OpenFile(self.file.Name(), os.O_RDONLY, 0)
 }
 
 // replay requests starting at the given requestNumber and for the