Databases unplugged challenges in ubiquitous data management
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Databases Unplugged: Challenges in Ubiquitous Data Management. Michael Franklin UC Berkeley. “Gazillions of Gizmos”. “In ten years, billions of people will be using the Web, but a trillion "gizmos" will also be connected to the Web.” Asilomar Rep. on DB Research, Dec. 1998

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Databases Unplugged: Challenges in Ubiquitous Data Management

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Databases unplugged challenges in ubiquitous data management

Databases Unplugged:Challenges in Ubiquitous Data Management

Michael Franklin

UC Berkeley

Gazillions of gizmos

“Gazillions of Gizmos”

  • “In ten years, billions of people will be using the Web, but a trillion "gizmos" will also be connected to the Web.” Asilomar Rep. on DB Research, Dec. 1998

  • You’ve heard it before…

    • Smartphones, PDAs, Smartcards, badges, wearables, lightswitches, toasters, …

    • Worldwide sales of Internet-enabled appliances projected to grow from 5.9M units in 1998 to 55.7M units in 2002. IDC via H&Q report

M. Franklin, 12/17/99

An explosion in scale

An Explosion in Scale

(Picture is by way of Randy Katz)




Many people

per computer

One person

per computer

Scaled down

PCs, desktop


PC + Network



Many computers

per person

Time Sharing







M. Franklin, 12/17/99

Technical challenges

Technical Challenges

  • Disconnection/Weak Connection

    • Standard distributed database techniques break down.

  • Limited resources

    • Memory, CPU, Power, User Interface, Bandwidth

  • Movement/Location

    • Killer Mobile apps use current and future locations.

  • Scale

    • Number and diversity of devices.

  • Reliability - Palm Pilots don’t bounce.

M. Franklin, 12/17/99

But is mobile data mgmt needed

But, is Mobile Data Mgmt Needed?

  • “Fundamentally, the ability to access all information from anywhere and have ONE unified and synchronized information repository is critical to making appliances useful.” Hambrecht and Quist, iWord , March 1999

  • “All these information appliances have internal data that "docks" with other data stores. Each gizmo is a candidate for database system technology, because most will store and manage some information.” Asilomar Report

M. Franklin, 12/17/99

Road map

Road Map

  • Motivation

  • Alternative scenarios for mobile Databases

  • Technical/Research challenges

  • Some solutions

    • Consistency

    • Data Dissemination

    • Data Recharging

  • Conclusions

M. Franklin, 12/17/99

How will it happen

How Will it Happen?


  • SQL engine on the device (largely standalone)

  • Extension of enterprise infrastructure

  • Data Collection (device to infrastructure)

  • Data Dissemination (infrastructure to device)

  • PIM-driven information assistant

M. Franklin, 12/17/99

Sql engine on the device

SQL Engine on the Device

  • Reasonable for Palmtop — but probably not the toaster or light-switch…

  • Stand-alone with occasional synchronization.

  • Footprint versus functionality

    • Engine can be made surprisingly small (10-100s KB).

    • Sybase uses “take what you need” library approach

  • All major vendors are playing in this space:

    • Oracle Lite, Sybase SQL Anywhere, Informix/Cloudscape, DB2 for the Workpad, SQL Server for Windows CE

  • But, what is the killer app???

  • M. Franklin, 12/17/99

    Extension of enterprise

    Extension of Enterprise

    • Logical Progression?

      • Mainframe->Desktop->Palm

      • ERP-> Palm

    • Device becomes the endpoint of the enterprise infrastructure (queries and updates).

    • This is happening but must take into account fundamental limitations of the mobile platforms.

    • Again, examples exist, but the killer app has not yet emerged here.

    M. Franklin, 12/17/99

    Data collection devices

    Data Collection Devices

    • Inventory Management/Tracking/Sensors/Census

    • Examples: Symbol technologies --- Palm with a bar code scanner; more futuristic: smart dust.

    • Asymmetric (device to server) data flow/usage dictates system architecture.

    • Many applications exist, but no clear need for full function DBMS on the device.

    • Server-side DB must handle datastreams

    M. Franklin, 12/17/99

    Data dissemination

    Data Dissemination

    • Many Potential Apps

      • stock and sports tickers

      • traffic information systems

      • software distribution

      • news and/or entertainment delivery

    • Asymmetric (server to devices) data flow/usage dictates system architecture.

    • No clear need for full function DBMS on the device, but intelligent caching and filtering on device is crucial.

    M. Franklin, 12/17/99

    Personal information management

    Personal Information Management

    • PIM is the killer app for mobile devices.

    • So, use PIM to drive the data management architecture.

    • Example: IBM’s Active Calendar

      • Calendar provides semantic information on what information will be needed when (and where).

      • Use this information to pre-stage information from the fixed infrastructure.

    • This seems to be the most promising approach for driving device DB functionality.

    M. Franklin, 12/17/99

    Research issues

    Research Issues

    • Transactions (not likely) and Consistency.

    • Distribution of function

      • how to split query functionality?

      • adaptive??

    • New Querying and Access Models

      • info filtering and dissemination

      • location centric/movement

      • triggers/pervasive (invasive?) computing

      • Evidence Accrual – killer app: dating game

    • Availability and Recovery

    M. Franklin, 12/17/99

    Data caching and consistency

    Data Caching and Consistency

    • How to keep distributed data consistent?

    • Centralized algorithms require connectivity at specific times.

    • Alternative: Epidemic Algorithms(Peer-to-peer)

      • Conflict detection: timestamps, version vectors,…

      • Conflict Handling (update commitment):

        • Optimistic (resolution) - Manual except in limited domains,

        • Pessimistic (avoidance) - primary copy, write-all or voting-based.

    M. Franklin, 12/17/99

    Epidemic protocol illustration

    Epidemic Protocol Illustration

    (Picture is by way of Ugur Cetintemel)


    M. Franklin, 12/17/99

    Deno cetintemel and keleher

    Deno - Cetintemel and Keleher

    Pessimistic, Asynchronous (epidemic), voting-based

    “Bounded” weighted-voting:

    • Each replica is assigned a currency cis.t. 0 ci  1.0

    • Total currency in the system is bounded, i.e., ci=1.0

    • Currency can be re-distributed for optimization or planned disconnection.

      An update’s life:

    • Sites issue tentative updates

    • Updates and votes are propagated in a pair-wise fashion

    • Updates gather votes as they pass through sites

    • An update commits when it gathers plurality of votes

    M. Franklin, 12/17/99

    Decentralized update commitment

    Decentralized Update Commitment

    • An update u wins an election with plurality

    • A site s maintains:

      • votes(u): the sum of votes u gained so far

      • unknown: the sum of votes unknown to s

        (i.e., 1.0 –  votes(u),for u)

    • u commits iff for all u’ <> u,

      votes(u) > votes(u') + unknown and

      votes(u) > unknown

      Issues: time to commit; abort rates





    (s1, 0.20, u1)

    (s5, 0.20, u1)

    (s6, 0.15, u2)

    (s1, 0.20, u1)

    (s5, 0.20, u1)

    (s1, 0.20, u1)

    (s5, 0.20, u1)

    (s6, 0.15, u2)

    (s2, 0.15, u1)

    (s1, 0.20, u1)

    (s4, 0.20, u2)

    (s6, 0.25, u3)

    (s2, 0.25, u2)

    (s1, 0.20, u1)

    (s1, 0.20, u1)

    (s4, 0.20, u2)

    (s6, 0.25, u3)

    (s1, 0.20, u1)

    (s4, 0.20, u2)

    (s1, 0.20, u1)

    votes(u1) = 0.20

    votes(u1) = 0.20

    votes(u1) = 0.40

    unknown = 0.80

    votes(u1) = 0.20

    votes(u2) = 0.20

    unknown = 0.80

    votes(u1) = 0.40

    votes(u2) = 0.15

    unknown = 0.60

    votes(u1) = 0.20

    votes(u2) = 0.20

    votes(u3) = 0.25

    votes(u1) = 0.55

    votes(u2) = 0.15

    votes(u1) = 0.20

    votes(u2) = 0.45

    votes(u3) = 0.25

    unknown = 0.60

    unknown = 0.45

    unknown = 0.30

    unknown = 0.35

    unknown = 0.10

    u1 commits!

    u2 commits!

    M. Franklin, 12/17/99

    Semantic caching dar et al

    Semantic Caching - Dar et al.

    • Idea: Maintain description of cache contents as a set of logical predicates rather than a list of items.

    • Potential advantages:

      • Less overhead with no need for static clustering (reduces bandwidth requirements).

      • Describe missing items with logical remainder query.

      • Application/Environment specific replacement functions --- e.g. considering direction and velocity.

    • Issues:

      • controlling complexity of cache descriptions

      • interacting with real database systems

    M. Franklin, 12/17/99

    Dissemination based info sys dbis

    Dissemination-Based Info Sys (DBIS)

    1) Push vs. Pull is just one dimension along which to compare data delivery mechanisms.

    - We’ve identified three.

    2) Different mechanisms for data delivery can (and should) be applied at different points in the system.

    - Select components from toolkit.

    Franklin and Zdonik - Framework in OOPSLA 97,

    Toolkit description and demo in SIGMOD 99.

    M. Franklin, 12/17/99

    Dbis framework

    DBIS Framework

    • An architecture that combines data delivery techniques for responsive client access.

    • 3 types of nodes:

      • Data sources

      • Clients

      • Information brokers (can add value)

    • Any data delivery mode can be used.

      • Network transparency

    • Possibly dynamic.

    M. Franklin, 12/17/99

    Delivery options













    Delivery Options























    M. Franklin, 12/17/99

    Network transparency




    Network Transparency

    The type of a link matters only to nodes on each end

    M. Franklin, 12/17/99

    Dbis example

    Proxy cache

    Proxy cache

    Proxy cache

    DBIS Example

    An example:

    Unicast pull

    Unicast pull

    1-to-n push



    Can vary dynamically

    Unicast pull

    M. Franklin, 12/17/99

    Dbis research issues

    DBIS Research Issues

    • Each data delivery mechanism has unique aspects

      • Broadcast Disks - sched., caching, prefetching,updates

      • On-demand Broadcast -scheduling, data staging

      • Publish/Subscribe-large-scale filtering, channelization

    • Security/Fault-tolerance/Reliability

    • End-to-End network design and control

    • Fundamental performance tradeoffs

    • Exploiting existing and emerging technologies

    M. Franklin, 12/17/99

    Data recharging

    “Data Recharging”

    • Mobile devices require 2 resources: power and data

      • It is impractical to be continuously connected to fixed sources of these.

    • Devices cope with disconnection using caching:

      • Power cached in rechargeable batteries

      • Data cached in hot-synched memory

    • Ideal: make recharging data as simple as power:

      • Anywhere (with adapters), anytime, flexible connection duration

    • Joint work w/ Mitch Cherniack and Stan Zdonik getting underway

    M. Franklin, 12/17/99

    Data recharging research agenda

    Data Recharging - Research Agenda

    • Profile Definition and Maintenance

    • Update Storage and Preparation

    • Efficient integration of "recharge" updates with existing cached data.

      • Recharge, Trickle Charge, Jump Start...

    • Consistency Guarantees

    • Global Data Staging

    • Approaches will be driven by (mostly PIM) applications.

    M. Franklin, 12/17/99



    • Lots of plausible/useful Mobile data architectures.

      • For many, the applications exist today

      • Each has its own set of fascinating research opportunities.

    • PIM is the killer app for mobile data access.

      • It can be used to drive the integration with enterprise and Internet data sources.

    • Successful MDA work lies at the intersection of communications and data management rather than exclusively in either camp.

    M. Franklin, 12/17/99

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