Value of Non-Functional Qualitites of Cloud StoragePresentation Transcript
Value of Non-functionalQualities of Cloud Storage First Thoughts / Brain Teaser
Retrospectivestarted with Cassandra and consistency trade-offscost for higher consistency level is costs of additional serversended up juggling with throughput, latency +consistency level
Why determine the value of non-fct.ies? }measuring non-fct. qualities e.g. Davids consistency benchmark, YCSB Ho to derive anmodifying non-fct. qualities optimal setup? e.g. Markus & Michaels storage tuningnon-fct. qualities: e.g. consistency, throughput, latency
FocusFocus on 3 important non-fct. properties of Cloud storage: latency throughput consistency
Latency effectwaiting for a responsemeasurablein time units
Consistency effectserver-side inconsistencies until eventually...access to stale serverinconsistency windowmeasurable 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!
Influence on non-fct. qualities1. parameters can be modified in Cloud storage2. non-fct. qualities react on parameter changes3. every parameter setting results in (l, t, c) outcome = (l, t, c)
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 mapparameter optimization:Songyun Duan, Vamsidhar Thummala, and Shivnath Babu. 2009. Tuning databaseconfiguration parameters with iTuned. Proc. VLDB Endow. 2, 1 (August 2009),1246-1257.
How to find the value? A formula?
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!
Determine the value of non-fct. qualities!measuring non-fct. qualitiese.g. Davids consistency benchmark }modifying non-fct. qualities everythinge.g. Markus & Michaels storage tuning perfect?optimize non-fct. qualitiesassuming a formula is defined
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?
Effects of (l, t, c) in e-business context ... become more specific! e-business case: online shop latency patience, 4 sec rule  throughput no response, lost sale consistency misinformation, over-sell Jupiter Research (2006), Retail Web Site Performance: Consumer Reaction to a Poor Online ShoppingExperience, Vendor Research commissioned by Akamai. (http://www.akamai.com/4seconds).
A formula in e-business context
Requirements for approach1. Probabilities must be determined. Big Tasks!2. Costs/benefits must be determined.3. Cost/Benefit relations must be expressed in a formula. or use standard formula?
Outlook/Open QuestionsRight 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.
One step further...self-optimizing Cloud storagethat minimizes business risks and benefitsaccording to the users parameters
Thank You!Questions / Discussion...
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