Relevant Systems Issues

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OSKI - Open Shared Kalendaring Infrastructure
Jason I. Hong Brad Morrey Mark Newman CS262
Operating Systems Fall 1998
or, building partially disconnected, highly
available, fault-tolerant, and scalable groupware
systems in a single semester
Relevant Systems Issues
Motivation
1. A Group Calendar application available through
web and partially disconnected portable
information appliances will be a generally useful
application 2. Explore building applications for
information appliances and away from desktop
(Post-PC) 3. Explore building scalable, highly
available, fault tolerant apps (Ninja)

• Data Consistency
• Relaxed consistency for performance
• Data is cached in all the tiers, eventually
  consistent
• No direct access to database, remote data
  servers only
• Sync Service and Disconnected Cache Manager
  resolves
• data conflicts in infrastructure and info
  appliance. All
• conflict resolution policies implemented in
  Sync Service.
• Extensibility
• Each type of information appliance needs its own
  type
• of Disconnected Cache Manager
• Each information appliance has its own
  Disconnected
• Cache Manager on machines you sync on.
  Disconnected
• Cache Manager is point-of-entry into system for
  devices.
• Future
• User Authentication
• High Availability, Fault-Tolerance, and
  Scalability
• Disconnected Cache Managers for New Devices

OSKI System Architecture
Architecture 1. Three-tier system to access
calendar data 2. User Service manages all user
data and prefs 3. Sync Manager / Disconnected
Cache Manager for partially disconnected
devices 4. Virtual Calendars aggregate individual
calendars and subscriptions 5. Notifications
for new events, auto accept / deny 6. Access
control lists for event visibility and access
Design Goals 1. Highly available, fault-tolerant,
scalable service 2. Scale for large number of
users and wide area 3. Disconnected operation /
eventually consistent 4. Work with existing
software (desktop / Pilot) 5. Provide rich
mechanism, minimal policy 6. vCalendar 1.0
Compliant
Tier 2 Data Objects
Tier 3 Database
Tier 1 Application Objects
Ask a User Service where a users home calendar
is located. If needed, redirect query like DNS
or LDAP.
Connected Access to OSKI
User Service
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Ask a Calendar Service for a users calendar.
2
User (Remote)
User (Local)

• Virtual Calendar created from
• All calendars owned by user
• New events in subscriptions
• All existing event notifications

Clients
NinjaRMI
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Java Applet
What We Learned
VirtualCalendar
Calendar Service
Disconnected Access to OSKI

• Lack of Post-PC tools increases development
  complexity
• Separating system properties (e.g. high
  availability) from
• functionality simplifies design, saving time
  and effort
• Designing application interfaces is challenging
• Designing for extensibility and flexibility is
  very difficult
• Conforming to standards is very time-consuming
• Supporting legacy systems also very
  time-consuming
• Build one to throw away...

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HotSync is initiated
Disconnected Cache Manager (Pilot)
Disconnected Cache Manager is the bridge between
device and infrastructure. Converts device date
format to OSKI format and detects changes.
2
OR
Virtual Calendar (Remote)
Virtual Calendar (Local)
Disconnected Cache Manager (Toaster)
NinjaRMI
Sync Service handles conflict resolution logic.
3
Disconnected Cache Manager (Barney)
Disconnected Devices
VirtualCalendar
vCalendar Compliant Calendar App
Calendar Service
Disconnected Cache Manager (WinCE)
Virtual Calendar generated same as above.
Differences between the infrastructure and
device are resolved.
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