QoS Aware Scheduling in a Cluster-Based Web Server

Jiani Guo

Architecture LabDepartment of Computer Science and Engineering

University of California, Riverside

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Reference

Performance Guarantees for Cluster-Based Internet Services, ICDCS 2003

Chang Li, Gang Peng, Kartik Gopalan

Tzi-cker Chiuh

State University of New York at Stony Brook

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Web Services

Courtesy: Performance Guarantees for Cluster-Based Internet Services, Chang Li.

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Differentiated ServiceA system is said to be capable of affording differentiated service among service classes if The system permits its resources to be proportioned among the

service classes Given sufficient request load, a service class receives at least as

much resources as were assigned to it irrespective of the load on other service classes

Resources not used by some service class may be distributed among other service classes.

QoS Metrics The number of generic URL requests per second A generic URL request represents an average web site access

which is assumed to take 10 msec of CPU time, 10 msec of disk channel usage time and 2000-bytes of network bandwidth

For example: QoS requirement is 50 GRPS, which means 500 msec of CPU time, 500 msec of disk access time and 100 Kbytes of the network bandwidth

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Scheduling Framework

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Request schedulingRequest selection

Weighted round robin (WRR) No idea about the resource a request will consume on dispatching it

Predict per-request resource usage using history Feedback to correct the prediction

Server node selection Load balancing among server nodes (Least Load First) Select a node based on resource usage accounting What to account

CPU, disk and network bandwidth Accounting granularity

Per-request Per-server Per process-set

Courtesy: Performance Guarantees for Cluster-Based Internet Services, Chang Li.

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Performance Isolation

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Performance deviation from ideal reservation

Averaging Interval (secs)

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My Previous Work on Scheduling:Scheduling Multimedia Jobs among Servers

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Transcoding Workload

A media unit is a Group Of Pictures(GOP) of MPEG streamA media unit can be transcoded independently by any Worker in the cluster. Transcoding one media unit is considered an independent job.No communication is required among jobs.Each job consumes similar amount of processing time.Consecutive media units in a stream are preferred to be processed in order.

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Load Balancing Schemes

How to take QoS into consideration? Streams make reservations Received service is proportional to the

reservations

Computing Server

Scheduler

Unit Buffer

Retriever

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.

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fetch a unit Find an available

Computing Server

Send the unit

Media ServerComputing Server

Computing Server

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Framework of Fair Scheduling