evaluating content management techniques for web proxy caches
DESCRIPTION
Evaluating Content Management Techniques for Web Proxy Caches. Martin Arlitt, Ludmila Cherkasova, John Dilley, Rich Friedrich and Tai Jin Hewlett-Packard Laboratories 4th International WWW Caching Workshop 元智大學資訊工程所 系統實驗室 陳桂慧 1999.10.06. Outline. Key workload characteristic - PowerPoint PPT PresentationTRANSCRIPT
Evaluating Content Management Techniques for Web Proxy Caches
Martin Arlitt, Ludmila Cherkasova, John Dilley, Rich Friedrich and Tai Jin
Hewlett-Packard Laboratories
4th International WWW Caching Workshop
元智大學資訊工程所 系統實驗室陳桂慧
1999.10.06
Outline
• Key workload characteristic• Experimental design • Simulation results• Conclusion
Key Workload Characteristics
• Cacheable objects• Object set sizes• Object sizes• Recency of reference• Frequency of reference• Turnover
Experimental Design
• Cache size– 256 MB, 1 GB, 4 GB, 16 GB, 64 GB, 256 GB and
1TB…...
• Cache replacement policy– LRU, SIZE, GD-Size, LFU, GDSF, LFU-DA
– LAT, HYB
• Performance metrics– Hit rate
– Byte hit rate
Replacement Algorithm (1)
• Least-Recently-Used (LRU)– replaces the object requested least recently.
• SIZE– replaces the largest object.
• LFU– replaces the least frequently used object.
• GreedyDual-Size (GD-Size)– replaces the object with the lowest utility.
– Ki = Ci / Si + L
Replacement Algorithm (2)
• GreedyDual-Size with Frequency (GDSF)– Ki = Fi * Ci / Si + L
• Least Frequently Used with Dynamic Aging(LFU-DA)– Ki = Ci * Fi + L
Hybrid Algorithm (HYB)
• Motivated by Bolot and Joschka’s algorithmW1rtti + 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
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
• Comparison of existing replacement policies
GD-Size(1)LFU-AgingSIZELFUGD-Size(P)LRU
LFU-AgingGD-Size(P)LRULFUGD-Size(1) SIZE
• Comparison of proposed policies to existing replacement policies
GDSF-HitsGD-Size(1)LFU-AgingLFU-DAGD-Size(P)LRU
LFU-AgingLFU-DAGD-Size(P)LRU GDSF-HitsGD-Size(1)
Virtual Caches
• An approach that can focus on both of high hit rates and high byte rate.– each virtual cache (VC) is then managed with its own rep
lacement policy. • initially all objects are added to VC 0,
• replacements from VC i are moved to VC i+1,
• replacements from VC n-1 are evicted from the cache.
• all objects that are reaccessed while in the cache (i.e., cache hits) are reinserted in VC 0 .
– this allows in-demand objects to stay in the cache for a longer period of time.
GDSF-HitsVC-HB-75/25VC-HB-50/50VC-HB-25/75LFU-DALRU
LFU-DAVC-HB-25/75VC-HB-50/50VC-HB-75/25LRUGDSF-Hits
• Analysis of Virtual Cache Performance – VC0 using GDSF-Hits, VC1 using LFU-DA.
• Analysis of Virtual Cache Management – VC0 using LFU-DA, VC1 using GDSF-Hits.
GDSF-HitsVC-HB-25/75VC-HB-50/50VC-HB-75/25 LFU-DALRU
LFU-DAVC-HB-25/75VC-HB-50/50VC-HB-75/25GDSF-HitsLRU
• Analysis of Virtual Cache Management – effects of VC order on performance
VC-BH-25/75VC-HB-75/25VC-BH-50/50VC-HB-50/50 VC-BH-75/25VC-HB-25/75
VC-HB-25/75 VC-BH-75/25 VC-HB-50/50 VC-BH-50/50VC-HB-75/25VC-BH-25/75
Conclusion
• Size-based policies achieve higher hit rates than other policies.
• Frequency-based policies are more effective at improving the byte hit rate of a proxy cache.
• Virtual caches as an approach provide optimal cache performance for multiple metrics simultaneously.