This project (source code) strives towards understanding and improving collaboration in cloud storage services.

Background

Recently, cloud storage services provide the users with advanced functions of collaborative file editing -- a shared file is simultaneously edited by multiple collaborators. For transparency and user-friendliness, today’s cloud storage services do not ask users to use version control systems; instead, they implement their own heuristics for dealing with conflicts. The transparency, however, is also a weakness, as some existing practices may lead to unexpected and undesired experiences, such as wired conflicts (listed in Table 1). In this project, we attempt to investigate the underlying reasons for these anomalies and propose practical solutions.

Pattern 1: Losing updates Alice is editing a file. Suddenly, her file is overwritten by a new version from her collaborator, Bob. Once this happens, Alice loses her edits on the older version.	All studied services
Pattern 2: Conflicts despite coordination Alice coordinates her edits with Bob through emails to avoid conflicts by enforcing a sequential order. Every edit is saved instantly. Even so, conflicts still occur.	All studied services
Pattern 3: Excessively long sync duration Alice edits a shared file and confirms that the edit has been synced to the cloud. However, Bob does not receive the updates for an excessively long duration.	Dropbox, OneDrive, SugarSync Seafile, Box
Pattern 4: Blocking collaborators by opening files Alice simply opens a shared Microsoft Office file with- out making any edits. This mysteriously disables Bob's editing the file.	Seafile (only for Microsoft Office files)

Table 1: Common patterns of unexpected and undesired collaborative experiences.

Summary of Our Findings

Our study leads to a number of findings that explain the unexpected and undesired patterns described in Table 1.

• Majority of the mainstream cloud storage services do not use any form of locking to prevent conflicts.
• Resolving conflicts is painful.
• Many of the undesired experiences are caused by the poor implementation of message queues at the cloud side.
• Combining full-file sync and delta sync to update different sizes of files outperforms a single method.

Figure 1: The workflow and system components for supporting collaborative file editing in cloud storage services. The solid boxes denote the common components among all the studied services, whereas the dotted boxes denote components in specific services.

Optimizations

Driven by the findings, we propose two optimizations which are fully compatible with the workflow and system architecture of existing cloud storage services (cf. Figure 1):

• A file-level editing lock based on file editing status is a better option than the hard-coded locks used by some of the existing cloud storage services.
• The client should actively fetch the latest version of a collaborative file from the cloud before editing.

ConfilctReaper for Dropbox Windows PC

Integrated aforementioned optimizations, we build ConflictReaper to assist existing cloud storage services in a fully transparent and automatic manner. ConflictReaper is agnostic to the cloud-side implementation and is generically applicable to existing cloud storage services. We implement the Windows version of ConflictReaper for Dropbox. The real-world experiment shows that it prevents 91% conflicts with acceptable network/computation overhead.