optimizing index allocation for sequential data broadcasting in wireless mobile computing ming-syan...
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Optimizing Index Allocation for Sequential Data Broadcasting in Wireless
Mobile Computing
Ming-Syan Chen, Senior Member, IEEE, Kun-Lung Wu, Member, IEEE Computer Society, and Philip S. Yu, Fellow, IEEE
M9129022 郭文漢
Outline
1. Introduction
2. Preliminaries
3. Index Allocation for Skewed Data Access
4. Optimal Order for Sequential Data Broadcasting
Introduction
背景
建立 index tree
Algorithm CF Algorithm VF
Optimal orderfor sequential
data broadcasting
解決方法 效益
節省電力
Algorithm ORD
舊方法問題問題
不使用Data Access Skew
有限電力
Introduction
A mobile client to be able to operate in two different modes: doze mode and active mode.
The structure of an index tree determines the index probing scenario to switch between the doze and the active modes for data access under such an indexed broadcasting.
Data Access Skew : The access frequencies of different data records are usually different from one another.
Introduction
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I a1 R1 R2 R3 a2 R4 R5 R6 a3 R7 R8 R9
Indexed broadcastingIndex tree
Index probing scenario to data record R5
Preliminaries
A mobile client is assumed to use selective tuning to listen to indexed sequential data broadcasting.
Tuning time : The amount of time spent by a client to listen to the channel.
Access time : The time elapsed from the time a client wants an identified record to the time that record is downloaded by the client.
Preliminaries
Probe wait : The time from the point a client tunes in to the point when the first index is reached.
Bcast wait : Time duration from the point the first index is reached to the point the required record is obtained.
Preliminaries
Tuning timeClient
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Probe wait
Bcast wait
Index Allocation For Skewed Data Access
1. Imbalanced Index Tree Construction for Fixed Fanouts
2. Employing Variant Index Fanouts to Minimize Index Probes
3. Experimental Results on Index Allocation
Imbalanced Index Tree Construction for Fixed Fanouts
Algorithm CF will reduce the number of index probes for hot data while allowing more probes for cold data.
Algorithm CF : Use access frequencies to build an index tree with a fixed fanout d.
Algorithm CF (bottom up manner)
Step 1 : Every single node labeled with the corresponding access frequency.
Step 2 : Attach the d subtrees with the smallest labels to a new node. Label the resulting subtree with the sum of all labels from its d child subtrees.
Step 3 : n=n-d+1. If n=1 stop else goto Step2
Algorithm CF
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Algorithm CF
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Corresponding data broadcasting sequence
Cost Model
Theorem 1: Given a fixed index fanouts, the average
number of index probes is minimized by using the index tree constructed by algorithm CF.
Cost model
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Employing Variant Index Fanouts to Minimize Index Probes
An efficient heuristic algorithm VF to build an index tree with variant fanouts.
We want data records to stay as close to the root as possible.
Algorithm VF strikes a compromise between these conflicting factors( larger fanouts) and minimizes the average cost of index probes.
Employing Variant Index Fanouts to Minimize Index Probes
1 2
Lemma 1.
Suppose that node r has m child nodes, , , ..., ,
which are sorted according to descending order of Pr( ),
1 , i.e. Pr( ) Pr( ) if and only if j .Then, the
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Employing Variant Index Fanouts to Minimize Index Probes
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Employing Variant Index Fanouts to Minimize Index Probes
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Employing Variant Index Fanouts to Minimize Index Probes
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Algorithm VF (top down manner)
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Algorithm VF:
Step 1:Assume that , , ..., and have been sorted
according to descending order of Pr( ), 1 .
Step 2:Partition( , , ..., ).
Step 3:Report the resulting index tree.
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Algorithm VF
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Procedure Partition( , , ..., ):
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2.If y(i ) 0, then return.
3.Attach nodes , , ..., under a
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Algorithm VF
Algorithm VF
Algorithm VF
Algorithm VF
Algorithm VF
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Experimental Results on Index Allocation
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Experimental Results on Index Allocation
Optimal Order for Sequence Data Broadcasting
1. Ordering Broadcasting Data to Minimize Data Access Time
2. Experimental Results on Order of Broadcasting
3. Remarks
Ordering Broadcasting Data to Minimize Data Access Time
Ordering Broadcasting Data to Minimize Data Access Time
Algorithm ORD
Algorithm ORD
Algorithm ORD
Experimental Results on Order of Broadcasting
Remarks
Algorithm Complexity Operation
CF sorting
VF recursive
ORD sorting
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