Palantír: Coordinating Distributed CMWorkspaces Anita Sarma, André van der Hoek Institute for Software Research University of California, Irvine {asarma,

A Typical Development Scenario CM repository Pete’s workspace CBA Ellen’s workspace ECD

Problem! A CM workspace in reality provides two kinds of isolation: –Good isolation  Shields current work from others changes –Bad isolation  Hides knowledge of what artifacts other developers are changing Break bad isolation, such that developers are aware of each other’s changes, but current work remains shielded from other people’s changes

The Solution New situation: Share information when others perform CM operations, and not just when I perform a CM operation Old situation: Information available only when I carry out a CM operation or explicitly request information CM repository CM repository

Many Difficult Questions Which information must be shared? How is the information presented? How can information overload be avoided? Can this approach scale? Does it actually help developers coordinate better? Goal: demonstrate feasibility of workspace awareness first!

Palantír Architecture CM repository Pete’s workspace C B A Ellen’s workspace E C D CM clientCM serverCM client Event wrapper Pete’s Visualizations Ellen’s Visualizations Palantír Internal State Palantír Internal State Event Service Event Service

Populating a Workspace Ellen populates her workspace with directories & files

Making Changes in the Workspace Ellen makes changes edit – creates redo.c write.c & dict.c ‘?’ denotes artifacts are undergoing changes Green color denotes changes by workspace owner

Committing Changes Ellen has finished her changes and committed them ‘?’ has changed to ‘!’ denoting changes are known Blue bars denote Severity of changes

More Changes (by Other Developers) Layers denote concurrent changes Other authors denoted by shades of red color Layers can be brought forward

Critical Feature: Pair-Wise Comparisons

Removing and Moving Artifacts Icons denote CM activities namely move and remove

Metadata Extensive metadata from CM systems Annotated with time of event occurrence Choice of author color from palette Back/ forward button for easy traversal

Scalability & Information Overload Application –Manage only relevant artifacts  Artifacts present in “my” workspace  Leverages event service filtering –Internal data structure versus visualization User cognition –Pair-wise comparisons –Stack shows linear evolution in time –Filter data per user criteria –Sorting of artifacts per severity / date

Experience Integration with two CM systems –CVS (optimistic) –RCS (pessimistic) Relatively easy to implement –500 lines of Java code each –Wraps each CVS/RCS command with a PalantirCVS/RCS command that invokes CVS/RCS and emits relevant events –Not complete, but the essence (~60%) is there

Related Work Configuration Management –Coven –COOP/Orm CSCW –MMM, ShrEdit –BSCW, “Edit wear and read wear” Software Evolution Visualization –Code decay –3D visualization

Conclusions Palantír is a prototype that… –…brings awareness to distributed CM workspaces –…shows pair-wise conflict –…provides a simple measure of severity Future Work –Examine change impact analysis for both atomic and compound artifacts –Additional visualizations –Case studies to determine effectiveness

Conflicts Do Happen! Large systems, multiple developers lead to conflicting changes.  Perry & Votta: “Files that have high degrees of parallel changes also tend to have more defects.”  Perry & Votta: “Overlapping time schedule of successive releases suggest that features for different releases are being developed almost concurrently.” Awareness of others changes helps in conflict resolution –Elvin’s success: “providing a way to gather and redistribute collaboration-focused information during everyday use.”

Conflicts Direct Conflicts: Overlapping changes to the same artifact Indirect Conflicts: Changes to one artifact modifying the behavior of another artifact –Implicit domain knowledge of developers. –Future Work: trace dependencies

Agile Processes Agile processes have fewer conflicts, but conflicts exist nonetheless Increased awareness necessitated by higher number of check-ins –Need to synchronize workspace only for significant changes, and not for all changes in the workspace A number of organizations, do not follow agile processes (NASA)

Event Frequency Event generated on check-in / check- out and other CM functions –Depending on the CM system in question. Push Model: events generated when others perform CM operations. Potential to leverage virtual file systems –Track smaller units of changes (save /edit)  Especially for severity calculations –Develop simple watch mechanisms

Existing CM functionality CVS watches – delivery mechanism is crude –Scaling problems Coven softlocks –Need to specify intended changes beforehand, which is difficult to do –Only watches for direct conflicts

P2P GrooveSiena Clients listening to events

Pair-Wise Comparisons dev 3 dev 1 ws owner dev 2 dev 4 dev1-dev2 dev1-dev3 dev1-dev4 dev1-All dev1-All: summarizes all comaprisons dev1-dev?: only those conflicts between dev1 and the other dev

Visualization Features Different views with different trade-offs –Amount of information versus level of intrusiveness –Scrolling marquee, fully graphical, tabular Configurable –Selection of relevant developers, events, timeframes Scalable –Internal data structure versus actual visualization –Pair-wise conflicts –Filter data on user criteria –Sorting per severity or change impact Extensive metadata