value of non-functional qualitites of cloud storage
TRANSCRIPT
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Value of Non-functional Qualities of Cloud Storage
First Thoughts / Brain Teaser
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Retrospective
started with Cassandra and consistency trade-offs
cost for higher consistency level is costs of additional servers
ended up juggling with throughput, latency + consistency level
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Why determine the value of non-fct.ies?
measuring non-fct. qualities
modifying non-fct. qualities
non-fct. qualities: e.g. consistency, throughput, latency
Ho to derive anoptimal setup?}e.g. David's consistency benchmark, YCSB
e.g. Markus & Michael's storage tuning
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Focus
Focus on 3 important non-fct. properties of Cloud storage:
latency
throughput
consistency
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Latency effect
waiting for a response
measurablein time units
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Throughput effect
full server, no response
measurablein % success
HTTP 503 Error
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Consistency effect
server-side inconsistencies until eventually...
access to stale server inconsistency window
measurable in multiple metricsin time units inconsistency window,in size of (numerical, version) difference
!!! server-side inconsistency can be covered by mechanisms, e.g. read repair -> effort!
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Influence on non-fct. qualities
1. parameters can be modified in Cloud storage
2. non-fct. qualities react on parameter changes
3. every parameter setting results in (l, t, c) outcome
= (l, t, c)
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Determine Optimal Value
measure parameter settings for (l, t, c) outcomes
generate value-outcome map: (l, t, c) -> value
find optimal value in value-outcome map
parameter optimization:Songyun Duan, Vamsidhar Thummala, and Shivnath Babu. 2009. Tuning database configuration parameters with iTuned. Proc. VLDB Endow. 2, 1 (August 2009), 1246-1257.
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How to find the value? A formula?
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Mind: Qualities do not fully compensate!There are min/max limits for non-fct. qualities!
There might be settings where 2 qualities are high!
Evaluation formula must consider that!
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Determine the value of non-fct. qualities!
measuring non-fct. qualities
modifying non-fct. qualities
optimize non-fct. qualities
everything perfect?}
e.g. David's consistency benchmark
e.g. Markus & Michael's storage tuning
assuming a formula is defined
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No meaning without business context!
Finding appropriate formula:Without understanding business impacts weights are arbitrary!
1. Consider the business case!
e.g. e-business case (immediate impact on business)
2. Insert actual costs into formula!
costs of latency, incosistencies, ...
What are the costs?
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Effects of (l, t, c) in e-business context... become more specific!e-business case: online shop
latencypatience, 4 sec rule [1]
throughputno response, lost sale
consistencymisinformation, over-sell
[1] Jupiter Research (2006), Retail Web Site Performance: Consumer Reaction to a Poor Online Shopping Experience, Vendor Research commissioned by Akamai. (http://www.akamai.com/4seconds).
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A formula in e-business context
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Requirements for approach
1. Probabilities must be determined.
2. Costs/benefits must be determined.
3. Cost/Benefit relations must be expressed in a formula. or use standard formula?
Big Tasks!
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Outlook/Open Questions
Right indicators/metrics measured?Throughput, Latency and Consistency are of great interest.
Can cost/prices always be determined?A business should know.
The perfect formula?No, only fair formula and model that helps making a decision.
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One step further...
self-optimizing Cloud storage that minimizes business risks and benefitsaccording to the user's parameters
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Thank You!
Questions / Discussion...
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Contact Me
For Questions, Discussions,or Initiating Research Exchange:
Michael MenzelResearch Center for Information Technology (FZI)Karlsruhe Institute of Technology (KIT)Englerstr. 1176131 Karlsruhe
Email: [email protected]