Value of Non-functional Qualities of Cloud Storage

First Thoughts / Brain Teaser

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

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

Focus

Focus on 3 important non-fct. properties of Cloud storage:

latency

throughput

consistency

Latency effect

waiting for a response

measurablein time units

Throughput effect

full server, no response

measurablein % success

HTTP 503 Error

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!

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)

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.

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. 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

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

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).

A formula in e-business context

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!

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.

One step further...

self-optimizing Cloud storage that minimizes business risks and benefitsaccording to the user's parameters

Thank You!

Questions / Discussion...

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: menzel@fzi.de