1 mobile data management sanjay kumar madria department of computer science university of...
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Mobile Data Management
Sanjay Kumar Madria
Department of Computer Science
University of Missouri-Rolla
Rolla, MO 65401
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Wireless Technologies Wireless local area networks
(WaveLan, Aironet – Possible Transmission error
Cellular wireless – Low bandwidth Packet radio (Metricom) -Low
Bandwidth Satellites (Inmarsat, Iridium) – Long
Latency
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Mobility Constraints CPU Power Bandwidth Delay tolerance Physical size Constraints on peripherals and
GUIs (modality of interaction) Locations change dynamically
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Why Mobile Data Mgmt?
Wireless Connectivity and use of PDA’s ,
handheld computing devices on the rise Workforces will carry extracts of corporate
databases with them Need central database repositories to serve
these work groups and keep them fairly
upto-date and consistent
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Applications Sales Force Automation - especially in
pharmaceutical industry, consumer goods,
parts Financial Consulting and Planning Insurance and Claim Processing - Auto,
General, and Life Insurance Real Estate/Property Management,
Maintenance and Building Contracting
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Data Processing Scenario One server or many servers (corporate data, inventory, HR, orders/billing) Shared Data Some Local Data per client , mostly subset of global data Need for accurate, up-to-date informationLimitations Short connect time per session Infrequent connections Clients may remain dormant for extended periods
of time Clients not reachable from servers at all times
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What is Mobility?
A device that moves– Between different geographical locations– Between different networks
A person who moves– Between different geographical locations– Between different networks– Between different communication devices– Between different applications
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Device mobility Plug in laptop at home/work on Ethernet
– Occasional long breaks in network access– Wired network access only (connected => well-
connected)– Network address changes– Only one type of network interface– May want access to information when no network is
available: hoard information locally Cell phone with access to cellular network
– Continuous connectivity– Phone # remains the same (high-level network
address)– Network performance may vary from place to place
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Device mobility….
Can we achieve best of both worlds?– Continuous connectivity of wireless access– Performance of better networks when available
Laptop moves between Ethernet, WaveLAN and Metricom networks– Wired and wireless network access– Potentially continuous connectivity, but may be
breaks in service– Network address changes– Radically different network performance on different
networks
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People mobility Phone available at home or at work
– Multiple phone numbers to reach me– Breaks in my reachability when I’m not in
Cell phone– Only one number to reach me– Continuously reachable– Sometimes poor quality and expensive connectivity
Cell phone, networked PDA, etc.– Multiple numbers/addresses for best quality
connection– Continuous reachability– Best choice of address may depend on sender’s
device or message content
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Mobility means changes
How does it affect the following? Hardware
– Lighter– More robust– Lower power
Wireless communication– Can’t tune for stationary access
Network protocols– Name changes– Delay changes– Error rate changes
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Changes…... Fidelity
– High fidelity may not be possible Data consistency
– Strong consistency no longer possible Location/transparency awareness
– Transparency not always desirable Names/addresses
– Names of endpoints may change Security
– Lighter-weight algorithms– Endpoint authentication harder– Devices more vulnerable
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Changes…... Performance
– Network, CPU all constrained– Delay and delay variability
Operating systems– New resources to track and manage: energy
Applications– Name changes– Changes in connectivity– Changes in quality of resources
People– Introduces new complexities, failures, devices
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Example changes Addresses
– Phone numbers, IP addresses Network performance
– Bandwidth, delay, bit error rates, cost, connectivity Network interfaces
– PPP, eth0, strip Between applications
– Different interfaces over phone & laptop Within applications
– Loss of bandwidth triggers change from color to B&W
Available resources– Files, printers, displays, power, even routing
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Most RDBMS vendors support the ISDB scenario - but no design and optimization aids Specialized Environments for ISDB apps:
Sybase Remote ServerSynchrologic iMOBILEMicrosoft SQL server - mobile app supportOracle LiteXtnd-Connect-Server (Extended
Technologies)Scoutware (Riverbed Technologies)
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Personal Communication System Personal Communication System (PCS)(PCS)
Wireless Components
BS
MSC (MTSO)
MS Wirelesscomponent
MS
Cell
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Personal Communication System Personal Communication System (PCS)(PCS)
Mobile cellsMetropolitan area Metropolitan area
Coverage area in one cell Coverage area in three cells
BS
BSBSBase Station
Large cells.Low density
Small cells.High density
Smaller cells.Higher density
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Personal Communication System Personal Communication System (PCS)(PCS)
Mobile cells
The entire coverage area is a group of a number of
cells. The size of cell depends upon the power of
the base stations.
PSTNMSC
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Personal Communication System Personal Communication System (PCS)(PCS)
Frequency reuse
61
7
54
3
2
61
7
54
3
2
61
7
54
3
2
D A
AA
AA
AA
NR
D3
D = distance between cells using the same frequencyR = cell radiusN = reuse pattern (the cluster size, which is 7).
Thus, for a 7-cell group with cell radius R = 3 miles, the frequency reuse distance D is 13.74 miles.
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Personal Communication System (PCS)Personal Communication System (PCS)
Problems with cellular structure
How to locate of a mobile unit in the entire coverage area?
Solution: Location management
How to maintain continuous communication between two parties in the presence of mobility?
Solution: Handoff
How to maintain continuous communication between two parties in the presence of mobility?
Solution: Roaming
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Personal Communication System Personal Communication System (PCS)(PCS)
HandoffA process, which allows users to remain in touch, even
while breaking the connection with one BS and
establishing connection with another BS.
Old BS New BS
MSC
Old BS New BS
MSC
MSC
Old BS New BS New BSOld BS
MSC
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Personal Communication System Personal Communication System (PCS)(PCS)
Handoff
To keep the conversation going, the Handoff
procedure should be completed while the MS (the
bus) is in the overlap region.
G
Old BS New BS
Cell overlap region
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Personal Communication System Personal Communication System (PCS)(PCS)
Handoff types with reference to the network
Intra-system handoff or Inter-BS handoff
The new and the old BSs are connected to
the same MSC.
Old BS New BS
MSC
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Personal Communication System Personal Communication System (PCS)(PCS)
Intra-system handoff or Inter-BS handoff
Steps
1. The MU (MS) momentarily suspends
conversation and initiates the handoff
procedure by signaling on an idle (currently
free) channel in the new BS. Then it resumes
the conversation on the old BS.
Old BS
MSC
New BS
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Personal Communication System Personal Communication System (PCS)(PCS)
Intra-system handoff or Inter-BS handoff
2. Upon receipt of the signal, the MSC transfers the encryption
information to the selected idle channel of the new BS and
sets up the new conversation path to the MS through that
channel. The switch bridges the new path with the old path
and informs the MS to transfer from the old channel to the
new channel.
Old BS
MSC
New BS
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Personal Communication System Personal Communication System (PCS)(PCS)
Intra-system handoff or Inter-BS handoff
3. After the MS has been transferred to the new BS, it signals
the network and resumes conversation using the new
channel.
Old BS
MSC
New BS
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Personal Communication System Personal Communication System (PCS)(PCS)
Intra-system handoff or Inter-BS handoff
4. Upon the receipt of the handoff completion signal, the
network removes the bridge from the path and releases
resources associated with the old channel.
Old BS
MSC
New BS
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Personal Communication System Personal Communication System (PCS)(PCS)
Handoff types with reference to the network
Intersystem handoff or Inter-MSC handoff
The new and the old BSs are connected to
different MSCs.
BS1
MSC B
BS2
MSC A
BS1
MSC B
BS2
MSC A
PSTN
TrunkTrunk
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Personal Communication System Personal Communication System (PCS)(PCS)
Roaming
Administrative constraints
Billing.
Subscription agreement.
Call transfer charges.
User profile and database sharing.
Any other policy constraints.
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Personal Communication System Personal Communication System (PCS)(PCS)
Roaming
Technical constraints
Bandwidth mismatch. For example, European
900MHz band may not be available in other
parts of the world.
Service providers must be able to
communicate with each other. Needs some
standard.
Mobile station constraints.
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Personal Communication System Personal Communication System (PCS)(PCS)
RoamingTwo basic operations in roaming management are
Registration (Location update): The process of
informing the presence or arrival of a MU to a
cell. Location tracking: the process of locating the
desired MU.
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Personal Communication System Personal Communication System (PCS)(PCS)
Registration
Two-Tier Scheme
HLR: Home Location Register
A HLR stores user profile and the
geographical location.
VLR: Visitor Location Register
A VLR stores user profile and the current
location who is a visitor to a different cell that
its home cell.
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Personal Communication System Personal Communication System (PCS)(PCS)
Registration
Two-Tier Scheme steps. MU1 moves to cell 2.
MU1
MU1
Cell 1 Cell 2
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Personal Communication System Personal Communication System (PCS)(PCS)
Registration
Steps
1. MU1 moves to cell 2. The MSC of cell 2 launches a
registration query to its VLR 2.
2. VLR2 sends a registration message containing MU’s
identity (MIN), which can be translated to HLR address.
3. After registration, HLR sends an acknowledgment
back to VLR2.
4. HLR sends a deregistration message to VLR1 (of cell
1) to delete the record of MU1 (obsolete). VLR1
acknowledges the cancellation.
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Personal Communication System Personal Communication System (PCS)(PCS)
Location tracking
Steps
1. VLR of cell 2 is searched for MU1’s profile.
2. If it is not found, then HLR is searched.
3. Once the location of MU1 is found, then the
information is sent to the base station of cell 1.
4. Cell 1 establishes the communication.
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Personal Communication System Personal Communication System (PCS)(PCS)
Location trackingTwo-Tier Scheme steps location search
Source-mss
Destls
Sourcels
Id LSDest Dest-ls - -
Id HLSDest Dest-HLS - -
DestHLS
Id MSSDest Dest-mss - -
DestSrc
1
2
3
4
9
5
6
87
10
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Personal Communication System Personal Communication System (PCS)(PCS)
Location trackingTwo-Tier Scheme steps location update
New-lsOld-ls
HLS
MU
1
23
10
9
5
6
47
8
Id HLSMU HLS - -
Id MSSMU New-mss - -
Id LSMU New-ls - -
New-mss
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Mobile Database Systems (MDS)Mobile Database Systems (MDS)
A Reference Architecture (Client-Server model)
MSC MSC
DB DB HLR VLR
BSC BSC
DBS DBS
MU BS
MU
MU
BS
MU
BS
MU
Fixed host
Fixed host
PSTN
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Data Processing Issues Processing at the Server Processing at the Client Update Propagation and Installation Consistency Management Less Serious:
– Concurrent Transactions– Client Data Recovery
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Database Issues in Mobile Computing
Query and Transaction Processing Replication Management Location ManagementLimitations
– Data Distribution, Mobility Management and Scalability– Role of wireless medium in info distribution– Dealing with short battery life– Dealing with prolonged disconnection
Periods– Bandwidth Management
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Mobility Management andScalability Location management Changing topologies Handoffs Resource finding Replication Resource sharing
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Bandwidth Management
Clients assumed to have weak and/or
unreliable communication capabilities Broadcast--scalable but high latency On-demand--less scalable and requires
more powerful client, but better response Client caching allows bandwidth
conservation
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Energy Management
Battery life expected to increase by only
20% in the next 10 years Reduce the number of messages sent Doze modes Power aware system software Power aware microprocessors Indexing wireless data to reduce tuning
time
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Large Impact Distributed data management Querying wireless data Handling/representing fast-changing data Scale Tariff-driven query optimization Security User interfaces
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Query Processing
New Issues– Energy Efficient Query Processing
– Location Dependent Query Processing
Old Issues - New Context– Cost Model
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Location Management New Issues
– Tracking Mobile Users Old Issues - New Context
– Managing Update Intensive Location Information
– Providing Replication to Reduce Latency for Location Queries
– Consistent Maintenance of Location Information
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Transaction Processing
New Issues– Recovery of Mobile Transactions– Lock Management in Mobile Transaction
Old Issues - New Context Extended Transaction Models
– Partitioning Objects while Maintaining Correctness
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Dissemination-based Data Delivery Using Broadcast Disks
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Broadcast Disk Proposes a mechanism called Broadcast
Disks to provide database access to mobile clients.
Server continuously and repeatedly broadcasts data to a mobile client as it goes by.
Multiple disks of different sizes are superimposed on the broadcast medium.
Exploits the client storage resources for caching data.
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Server Broadcast Programs Data server must construct a broadcast
“program” to meet the needs of the client population.
Server would take the union of required items and broadcast the resulting set cyclically.
Single additional layer in a client’s memory hierarchy - flat broadcast.
In a flat broadcast the expected wait for an item on the broadcast is the same for all items.
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Server Broadcast Programs
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Server Broadcast Programs
Broadcast Disks are an alternative to flat broadcasts.
Broadcast is structured as multiple disks of varying sizes, each spinning at different rates.
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Server Broadcast ProgramsFlat Broadcast
Skewed Broadcast
Multi-disk Broadcast
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Server Broadcast Programs For uniform access probabilities a
flat disk has the best expected performance.
For increasingly skewed access probabilities, non-flat disk programs perform better.
Multi-disk programs perform better than the skewed programs.
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Server Broadcast ProgramsGenerating a multi-disk broadcast
Number of disks (num_disks) determine the number of different frequencies with which pages will be broadcast.
For each disk, the number of pages and the relative frequency of broadcast (rel_freq(i)) are specified.
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Server Broadcast Programs
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Client Cache Management Improving the broadcast for one
probability access distribution will hurt the performance of other clients with different access distributions.
Therefore the client machines need to cache pages obtained from the broadcast.
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Client Cache Management
With traditional caching clients cache the data most likely to be accessed in the future.
With Broadcast Disks, traditional caching may lead to poor performance if the server’s broadcast is poorly matched to the clients access distribution.
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Client Cache Management In the Broadcast Disk system, clients
cache the pages for which the local probability of access is higher than the frequency of broadcast.
This leads to the need for cost-based page replacement.
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Client Cache Management
One cost-based page replacement strategy replaces the page that has the lowest ratio between its probability of access (P) and its frequency of broadcast (X) - PIX
PIX requires the following:
1 Perfect knowledge of access probabilities.
2 Comparison of PIX values for all cache resident pages at cache replacement time.
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Client Cache Management Another page replacement strategy adds
the frequency of broadcast to an LRU style policy. This policy is known as LIX.
LIX maintains a separate list of cache-resident pages for each logical disk
Each list is ordered based on an approximation of the access probability (L) for each page.
A LIX value is computed by dividing L by X, the frequency of broadcast. The page with the lowest LIX value is replaced.
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Prefetching
An alternative approach to obtaining pages from the broadcast.
Goal is to improve the response time of clients that access data from the broadcast.
Methods of Prefetching:
Tag Team Caching
Prefetching Heuristic
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Prefetching Tag Team Caching - Pages continually
replace each other in the cache. For example two pages x and y, being
broadcast, the client caches x as it arrives on the broadcast. Client drops x and caches y when y arrives on the broadcast.
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Prefetching Simple Prefetching Heuristic Performs a calculation for each page that
arrives on the broadcast based on the probability of access for the page (P) and the amount of time that will elapse before the page will come around again (T).
If the PT value of the page being broadcast is higher than the page in cache with the lowest PT value, then the page in cache is replaced.
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Read/Write Case With dynamic broadcast there are three
different changes that have to be handled.
1 Changes to the value of the objects being broadcast.
2 Reorganization of the broadcast.3 Changes to the contents of the
broadcast.
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Conclusion
Broadcast Disks project investigates the use of data broadcast and client storage resources to provide improved performance, scalability and availability in networked applications with asymmetric capabilities.
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Mobility System conguration is no longer static:
the center of activity, the topology, the system load, and
locality, change dynamically need to search to locate objects various forms of heterogeneity
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Wireless Communications
offer less bandwidth more expensive less reliable Consequently, connectivity is weak and
often intermittent
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Portable Devices
light and small to be easily carried around Such considerations, in conjunction with a given
cost and level of technology ) mobile elements with less
resources (e.g., memory, screen size and disk capacity) reliance on battery can be more easily accidentally damaged,
stolen, or lost, thus, less secure and reliable
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Mobile units are still characterized as: unreliable and prone to hard failures,
i.e., theft, loss or accidental damage, resource-poor relative to static hosts. Examples: InfoPad [16] and ParcTab
[28] projects
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Adaptability A mobile system is presented with resources
of varying number and quality: Connectivity conditions vary from total
disconnections to full connectivity Available resources are not static either, for
instance a docked" mobile computer may have access
to a larger display or memory. the location of mobile elements changes and
so does the network conguration and the center of computational activity
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Example: during disconnection, a mobile host may work
autonomously, while during periods of strong connectivity, depend
heavily on the xed network sparing its scarce local resources
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Disconnections: disconnected operation - autonomous
operation of a mobile host during disconnection. Weak connectivity: Operation should be tuned
for communication environments characterized by low bandwidth, high latency, and expensive prices.
Mobility: Basic support such as as establishing new communication links as well as advanced support such as migrating executing processes and database transactions in progress.
Failure recovery: Since mobile elements are prone to hard failures, methods for failure handling and recovery are important.
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Data Dissemination by Broadcast
Pull-based data delivery or on demand data delivery: A client
explicitly requests data items from the server. Push-based data delivery: The server
repetitively broadcasts data to a client population without a specic
request. Clients monitor the broadcast and retrieve the data
items they need as they arrive.
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Applications: Dissemination-based: information feeds
such as stock quotes and sport tickets, electronic newsletters, mailing lists, traffic and weather information systems, cable TV on the Internet
Commercial Products for example: the AirMedia's Live Internet broadcast
network [6] Hughes Network Systems' DirectPC [26]
Teletext and Videotex systems [11, 28]
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The Datacycle project [16] at Bellcore: a database circulates on a high bandwidth network (140 Mbps). Users query the database by ltering information via special massively parallel transceivers.
The Boston Community Information System (BCIS) [18]:
broadcast news and information over an FM channel to clients
with personal computers equipped with radio receivers
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Hybrid Delivery Push vs Pull Push suitable when information is transmitted
to a large number of clients with overlapping interests the server saves several messages
the server is prevented from being overwhelmed by client requests.
Push is scalable: performance does not depend on the number of clients Pull cannot scale beyond the capacity of the server
or the network. In push, access is only sequential; Thus,
access latency degrades with the volume of data In pull, clients play a more active role
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Hybrid Delivery clients are provided with an uplink
channel, called backchannel, to send messages to the server. Sharing the channel : if the same channel is used for both
broadcast delivery and for the transmission of the replies to on
demand requests
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Use of the backchannel - to provide feedback and prole information to
the server - to directly request data Which pages? to avoid overwhelming the
server Page i not in cache and the number of items
scheduled to appear before i on the broadcast is greater than a
threshold parameter
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Selective Broadcast Broadcast an appropriately selected subset of items and provide the rest on demand In [25], the broadcast is used as an air-cache for storing frequently requested data. The broadcast content continuously adjusts to match the hot-spot of the database. The hot-spot is calculated by observing broadcast misses indicated by explicit requests for data not on the broadcast. In [19]: the database is partitioned into: a \publication group" that is broadcast and an \on demand" group. The criterion for partitioning is to minimize the backchannel requests while constraining the response time below a predened upper limit.
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On Demand Broadcast the server chooses the next item to broadcast
on every broadcast tick based on the requests for data it has
received Various strategies [28]: broadcast the pages
in the order they are requested (FCFS), or the page with the
maximum number of pending requests. A parameterized algorithm for large-scale
data broadcast based only on the current queue of pending
requests [7
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Organization of Broadcast Data
Access time: average time elapsed from the moment a client
expresses its interest to an item to the receipt of the item on the
broadcast channel Tuning time: the amount of time spent
listening to the broadcast channel Organize the broadcast to minimize
access and tuning time
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Efficient Concurrency Control for Broadcast EnvironmentsJayavel Shanmugasundaram
Arvind Nithrakashyap
Rajendran Sivasankaran
Krithi Ramamritham
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Outline Broadcast environments Inapplicability of existing techniques Suitable correctness criterion Mechanisms Performance Results Conclusion
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Why Broadcast Data? Millions of clients that need to see current
and consistent data Server handling all client requests
==> not scalable More scalable solution:
Periodically broadcast all data items Clients read items off broadcast Datacycle [Herman], Broadcast Disks
[Acharya]
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Example: eAuctions
Numerous potential clients
Only a small fraction contact server to offer bids
Need access to current and consistent data
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Broadcast Environment Characteristics
Large number of clients Mobile clients with scarce power resource
==> Low client to server bandwidth
Plentiful server to client bandwidth==> Asymmetric communication medium
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Mutually Consistent Reads
R(x) R(y) R(z)
time (broadcast cycles)
Are x, y, and z mutually consistent?
TrBegin TrEnd
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Outline Broadcast environments Inapplicability of existing techniques Suitable correctness criterion Mechanisms Performance Results Conclusion
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Why Not Traditional CC Techniques?
Approach 1: Dynamic conflict resolution – Excessive communication– e.g., locking:
• acquiring read locks by client transactions• server swamped with lock requests• client uses precious uplink bandwidth
Approach 2: Avoid potential serializability conflicts
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Schedules
C4W4(y)Server W2(x) C2
ClientA R1(y)R1(x)
time
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Serialization Orders
C4W4(y)Server W2(x) C2
ClientA R1(y)R1(x)
T2 T4
T4T1T2
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Serialization Orders
C4W4(y)Server W2(x) C2
ClientA R1(y)R1(x)
R3(x) R3(y)ClientB
T2 T4
T4T1T2
Even if ClientB does not exist, ClientA will have to abort transaction T1
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Serializability?
Serializability - a global property
All read only transactions:– Required to see same serial order of update
transactions, even if executing at different clients– Required to be serializable w.r.t. all update transactions,
even if updates do not affect values read
Inappropriate for broadcast environments
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Outline Broadcast environments Inapplicability of existing techniques Suitable correctness criterion Mechanisms Performance Results Conclusion
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Broadcast Data Requirements
Mutual consistency – server maintains mutually consistent data
– clients read mutually consistent data
Currency – clients see data that is current
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A Sufficient Criterion
• All update transactions are serializable.
• Each read-only transaction is serializable with respect to the update transactions it (directly or indirectly) reads from.
C4W4(y)Server W2(x) C2
ClientA R1(y)R1(x)
R3(x) R3(y)ClientB
T2T4
T4T1
T2T3
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A Sufficient Criterion
• All update transactions are serializable.
• Each read-only transaction is serializable with respect to the update transactions it (directly or indirectly) reads from.
external consistency [Weihl 87] update consistency [Bober and Carey 92]
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Implications
Decoupled correctness criterion– Clients need not communicate with server
or other clients
Weaker correctness criterion– Reduces unnecessary aborts
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Outline Broadcast environments Inapplicability of existing techniques Suitable correctness criterion Mechanisms Performance Results Conclusion
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The Algorithm F-Matrix
Server functionality Client functionality Nature of Control Information
– broadcast by the server with the data– helps clients determine consistency of
reads
Client read-only validation protocol
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Server Functionality
Ensures conflict serializability of update transactions
Broadcasts during each cycle– Committed values of data items at start of
cycle– Control matrix
Incrementally maintains control matrix as updates occur
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Client Functionalityconsult control information transmitted during that cycle to determine whether the read operation can proceed
if read operation cannot proceed the transaction is aborted.
Read
update tr : (write set + values) along with (read set + cycle numbers) sent to server
read tr : commit succeeds
Commit
Writeperformed on a local copy of the data item in the client.
no checks are made
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Control Matrix: Intuition
C4W4(y)Server W2(x) C2
Client R1(y)R1(x)
C4R4(x) W4(y)Server W2(x) C2
Client R1(y)R1(x)
T is currently reading yT had read xDid any tr that affected y change x after T read it?
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Control MatrixObjects: n objects all initialized at cycle 0
C: n x n control matrix
C(x,y) = max( cycle in which T commits ), where
T affects the latest committed value of y and also writes to x
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Precond. for Consistent ReadsT previously read x from broadcast cycle b
RT = set of (x ,b) pairs
C is the matrix at the beginning of current cycle
read y iff read-condition(y) holds:
forall (x,b) in RT, C(x,y) < b
i.e., no transaction that affected y wrote x after t read x
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Smaller Control Matrix
Partition objects into groups Control matrix: n x numgroups SC(x,s) = max y in s C(x, y)
Updating an object in s = update to any object in s
Fewer entries to transmit compared to Cgroup 1 group2
read-condition(y): forall (x , b) in RT SC(i , s) < b
T is currently reading yT had read xNo tr that affected any object in y ‘s group
changed x after T read it
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Group Size Increasing size of group =>
more unnecessary conflicts
Reducing size of group => increased control information overhead.
– n groups => F-Matrix– one group => Datacycle
• achieves serializability
Read-condition for Datacycle :
no previously read object has been updated
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R-Matrix
To achieve Mutual Consistency
Read condition:
objects previously read have not been updated by other transactions or
the object being read has not been updatedsince the beginning of the transaction
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Outline Broadcast environments Inapplicability of existing techniques Suitable correctness criterion Mechanisms Performance Results Conclusion
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Effect of Client Tr. Length
F-Matrix -- has best perf.-- scales very well
DatacycleR-MatrixF-MatrixF-Matrix-ideal
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Summary of Results
F-Matrix > R-Matrix > Datacycle
– Weaker abort condition leads to better response times
F-Matrix is highly scalable with respect to
– Client/Server transaction length
– Server transaction rate
– Number of Objects/Size of Objects
R-Matrix better only at very small object sizes
In many cases F-Matrix is very close to F-Matrix-ideal
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Conclusion
Need for mutual consistency + currency Efficient mechanism - F-matrix R-matrix is a low overhead alternative F-matrix delivers!
In Paper: Caching to exploit weak currency requirements
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Examples
Business data, e.g., Vitria, Tibco Election coverage data Stock related data Traffic information Electronic auctions
Data Server