Proxy caching the estimates page load delays
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Proxy Caching the Estimates Page Load Delays. Roland P. Wooster and Marc Abrams Network Research Group, Computer Science Department, Virginia Tech 元智大學 資訊工程所 系統實驗室 陳桂慧 1999.05.11. Outline. Related results Removal algorithms Latency Estimation Algorithm (LAT) Hybird Algorithm (HYB)

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Proxy Caching the Estimates Page Load Delays

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Proxy caching the estimates page load delays

Proxy Caching the Estimates Page Load Delays

Roland P. Wooster and Marc Abrams

Network Research Group,

Computer Science Department, Virginia Tech

元智大學 資訊工程所 系統實驗室

陳桂慧

1999.05.11


Outline

Outline

  • Related results

  • Removal algorithms

    • Latency Estimation Algorithm (LAT)

    • Hybird Algorithm (HYB)

  • Results of experiment


Proxy caching the estimates page load delays

  • A removal algorithm can optimize one of several measures:

    • minimize the number of bytes that travel over the Internet

    • minimize the number of hits to popular Web servers; or

    • minimize the time that end users wait for a document to load.


Related results

Related Results

  • The evidence in Williams et al [WILL96] is that proxy caches can

    • minimize server loads by using SIZE as a removal algorithm,

    • minimize wasted network bandwidth by using LFU, and achieve hit rates in the 20-50% range.


Latency estimation algorithm lat

Latency Estimation Algorithm (LAT)

  • clatj = (1-ALPHA) clatj + ALPHA sclat

  • cbwj = (1-ALPHA) cbwj + ALPHA scbw.

    • Clatj : estimated latency (time) to open a connection to the server

    • cbwj : estimated bandwidth of the connection

    • sclat and scbw : the connection establishment latency and bandwidth for that document are measured

  • di = clatser(i) + si/cbwser(i)

    • ser(i) : the server on which document i resides

    • si : the document's size

    • di : LAT selects for replacement the document i with the smallest download time estimate


Hybrid algorithm hyb

Hybrid Algorithm (HYB)

  • Motivated by Bolot and Joschka’s algorithm

    W1rtti + W2 si + (W3 + W4 si)/ti

    • ti : the time since the document was last referenced

    • rtti: the time it took to retrieve the document

  • (clatser(i) + WB/cbwser(i))(nrefi** WN)/ si

    • nrefi: the number of references to document i since it last entered the cache

    • si : the size in bytes of document i

    • WB and WN : constants that set the relative importance of the variables cbwser(i) and nrefj


Comparison to bolot and hoschka

Comparison to Bolot and Hoschka

  • Estimate the quantities on a per-server not a per-document basis.

  • Estimation algorithm uses history of references, rather than just the last reference.

  • HYB use the number of accesses to a document, rather than the last access time


Proxy caching the estimates page load delays

WorkloadModeReplacement Policies Parameter Values

1.VT-CS1onlineLAT,LFU,LRU,SIZE N/A

2.VT-CS2,VT-CS3 online HYB,LFU,LRU,SIZE WB=8Kb,

WN=0.9Kb,CONN=2Kb

3.VT-CS2,BU,VT-LIB replay HYB,LFU,LRU,SIZE WB=8Kb,

WN=0.9Kb,CONN=2Kb

4. VT-CS2,BU,VT-LIB replay HYB See Table 2

--------------------------------------------------------------------------------------------------------------

Table 1 : Experiments performed

Trial WB WN CONN

18 Kbyte 0.9 2 Kbyte

216 Kbyte 0.9 0.5 Kbyte

38 Kbyte 1.1 0.5 Kbyte

416 Kbyte 1.1 2 Kbyte

------------------------------------------------------------------------

Table 2: Weight settings for Exeriment 4 in Table 1.


Proxy caching the estimates page load delays

Variation of download time, workload VT-CS1, Experiment 1.


Proxy caching the estimates page load delays

Variation of download time, workload VT-CS2, Experiment 2


Experiment 3

Experiment 3

HRWHRTime

BetterWorse Better Worse Better Worse

VT-CS2 SIZE*LFU*LRU*SIZE*HYB* LFU*

HYB* LRU* LFU* HYB* SIZE LRU

BU SIZE *LFU *LRUSIZE *SIZE *LRU * HYB LRU HYB LFU HYB LFU

VT-LIB SIZE *LFU* LRULFU HYBLFU

HYB* LRU HYB SIZE* SIZE LRU


Experiment 4

Experiment 4

  • HR is always sensitive to weight WB,

  • Time is rarely sensitive to the weights, and

  • WHR is sensitive to WB and sometimes WN.


Conclusions

Conclusions

  • LAT, which estimates download time and replaces documents with shortest download time,

  • HYB, which combines estimates of the connection time of a server and the network bandwidth that would be achieved to the server with document size and number of document accesses since the document entered the cache.

  • Suggest : replacement only on estimated download time (algorithm LAT) is a bad idea.


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