Effective Data Man-agement Techniques

- In the view of Stream data한국기술교육대학교 컴퓨터공학부민준기

Stream data◦ A growing number of applications generate streams of data

Performance measurements in network monitoring and traffic management

Call detail records in telecommunications Transactions in retail chains, ATM operations in banks Log records generated by Web Servers Sensor network data

◦ Application characteristics Massive volumes of data (several terabytes) Records arrive at a rapid rate

1. Introduction

1. Introduction Traditional Data Processing

◦ Stable Repository◦ Query the data many times

Stream Data Processing◦ Data arrives continuously◦ Data is processed without the benefit of multiple

passes ◦ For stream data, users register queries priorly

2. Stream Data Manage-ment Using RDBMS

◦ Data streams as relation inserts, continuous queries as triggers or materialized views

◦ Problems with this approach Inserts are typically batched, high overhead Expressiveness: simple conditions (triggers), no built-

in notion of sequence (views) No notion of approximation, resource allocation Current systems don’t scale to large # of triggers

STREAM[2]◦ Stanford

Telegraph[3]◦ Research project in UC Berkeley

AURORA[1]◦ MIT, Brown University, Brandeis University

Stream Data Management Sys-tem

STREAM The Stanford Data Stream Management

System◦ Data streams and stored relations◦ Declarative language for registering continuous

queries CQL◦ Flexible query plans and execution strategies

Continuous monitoring and reoptimization subsystem◦ Aggressive sharing of state and computation

among queries◦ Load-shedding by introducing approximation◦ Tools to monitor and manipulate query plan

STREAM

Query Plan

Property Value

Legend

Join Selectivity

Rate of tuple flow

Queue size

Telegraph-CQ Research project in UC Berkeley challenges

◦ Adaptivity eddies : tuple routing and operator scheduling

◦ Shared continuous queries amortizing query-processing costs by sharing the execution of multiple long-

running queries

assumption of Telegraph’s design◦ very volatile, unpredictable environments

internet, sensor networks, wide-area federated S/W including peer-to-peer systems◦ performance is volatile

data rates change from moment to moment services speed up, slow down, disappear and reappear over time code behaves differently from moment to moment data quality changes from moment to moment

Telegraph-CQ

Aurora MIT, Brown University, Brandeis Uni-

versity Features

1.Designed for Scalablility: 2.QoS-Driven Resource Management3.Continuous and Historical Queries4.Stream Storage Management

Aurora

Scheduler

QOSMonitor

Box Processors

...

Buffer

Storage Manager

Persistent Store

…q1…q2

…qi

…q1

…qn

...

…q2

s

m...

È

s

.

.

.

È

Catalog

Router

inputs outputs

Aurora

Query Operators (Boxes)◦ Simple: FILTER, MAP◦ Binary: UNION, JOIN◦ Windowed: AGGREGATE, WSORT

App QoS...

...

App QoS...

App QoS

...

...

s

s

m

s

È

m

s

Slide

Tumble

m

s

Aurora

Stream data Processing The properties of stream data varies over time

◦ Adaptiveness to generate an efficient plan with respect to the change of data properties is required

◦ Improve the Performance of Stream Query Pro-cessing Operator Scheduling

(NEXT WEEK) Operator Ordering Query Optimization Query Index

Operator Scheduling Operator Scheduling

◦ Select one operator among executable operators Primitive scheduling Eddy[4] Chain[5] Train[6] Adaptive Scheduling[7]

O1

O3

O2

Stream Source

Queue

Queue Queue

Queue

Process scheduling From OS◦ FIFO

Tuples are processed in the order that they arrive Advantage

A consistent throughput◦ Round robin

Works by placing all runnable operators in a circular queue and allocating a fixed time slice to each

Advantage Avoidance of starvation

Disadvantage◦ Does not adapt at all changing stream conditions

Large Queue size, poor output rate

Premitive Operator Sched-uling

Eddy: Telegraph-CQ[4]Eddy :

◦ lottery-type sched-uler

◦ Adapting to Long Running Queries ready bit : indicate

which operators can be applied to a tuple

done bit : indicate the operators to which a tuple has al-ready been routed R

s(R.a > 10)

Eddy

s(R.b < 15) R1

R1

R1

R1a 5b 25

R2a 15

b 01 1 0 01 1 0 11 1 0 01 1 1 01 1 11Ready

Done

sasb sasb R

s(R.a > 10)

Eddy

s(R.b < 15)

R2

R2R2R2 R2

R2

SELECT *FROM RWHERE R.a > 10 AND R.b < 15

STREAM Purpose

◦ minimize memory utilization

Assumption◦ Operator time t◦ Operator selectivity s

Chain[5]

Progress chart◦ m+1 operator pointers (t0,s0),(t1,s1), … (tm,sm)◦ i th operator oi takes ti-ti-1 time with si/si-1 selectiv-

ity

Chain[5]

◦ For a point (t,s) where ti-1<= t< ti, the derivative with respect to the j th operator point where m>= j >= I, d(t,s,j) = -(s j-s)/tj-t

◦ The steepest derivative D(t,s) = maxm>=j>=i d(t,s,j)◦ Steepest Descent Operator point

SDOP(t,s) = (tb,sb) where b = min{j | m>= j >=i and d(t,s,j) = D(t,s)}◦ Lower envelop

Connect the sequence of SDOPs Chain

◦ Schedule for a single time until the tuple that lies on the seg-ment with the steepest slop in its lower envelope simulation. If there are multiple such tuples, select tuple which has the earliest arrival time

◦ Chain is optimal with respect to memory utilization in single stream query (e.g., simple selections)

Chain[5]

Extending Chain to Joins◦ (t,s): Process time t and selectivity s◦ Average number of tuples in S : LS◦ Window size(time) :t’◦ Input size : t’(LR+LS)◦ Output size : t’(LRaw(S) +LSaw(R))

where aw(s) is the semijoin selectivity of stream R with sliding windows for S.

◦ Time for run : t’(LRtR +LStS) Where tx is the average time to process a tuple from stream X

◦ Selectivity s for a join (LRaw(S) +LSaw(R) )/ (LR+LS)

◦ Processing time t for a join (LRtR +LStS)/ LR+LS

Chain[5]

Aurora data stream manager Two-Level Scheduling

◦ Which query to processing(i.e., select a query) Static: application-at-a-time

Use various scheduling policies(e.g., round robin) Dynamic: top-k spanner

QoS-driven◦ How selected query be processed

Operator scheduling

Train[6]

Operator scheduling◦ Traversing query tree◦ Three goals

Throughput Latency Memory requirement

◦ QoS driven scheduling

Train[6]

Min-Cost(MC)◦ Optimize per-output-tuple processing cost◦ Traverse the query tree in post-order

b4-b5- b3-b2-b6-b1

◦ Assume process cost per tuple p, a box call overhead o A selectivity is 1 Each operator has a queue with a single tuple

Total cost: 15p+5o Average output latency: 12.5p+o

Train[6]

Min-Latency(ML)◦ Average latency of the output tuples can be reduced by

producing initial output tuples as fast as possible◦ Output_cost(b): an estimate of the latency

where D(b) is the set of operators downstream from b◦ Under the same condition of MC

b1-b2-b1-b6-b1-b4-b2-b1-b3-b2-b1-b5-b3-b2-b1

◦ Total cost: 15p+15o◦ Average latency: 7.17p+7.17o

Train[6]

Min-Memory(MM)◦ Maximize the consumption of data per unit time◦ Expected memory reduction rates for b

where tsize(b) is the size of a tuple that reside on b’s input queue◦ Assume selectivity and cost:

b1=(0.9, 2), b2=(0.4,2) b3=(0.4, 3) b4=(1.0, 2) b5=(0.4,3), b6=(0.6,1) All tuple size is 1

◦ Mem_rr: 0.05, 0.3, 0.5, 0, 0.2, 0.4

◦ Memory requirement MM(36), MC(39), ML(40)

Train[6]

QoS driven scheduling

Each operator has priority= (utility, urgency)◦ Utility(b) = gradient(eol(b))

eol(b) = latency(b) + cost(D(b))Where D(b) is set of operators downstream from b and cost(D(b)) is

an estimate of how long it will take to processLatency(b) is average latency of tuples in input queue

◦ Urgency(b) = -est(b)where est(b) is an indication of how close a operator is to a critical point( a point where QoS changes sharply)

Priority(b) = (utility(b), -est(b))

Select operator having the highest utility and choose one hav-ing minimum slack time.

Train[6]

WORCESTER Polytechnic institute◦ Master thesis

Raindrop system No superior scheduling Diverse QoS requirements

◦ Output rate◦ Intermediate Query size◦ Tuple Delay

A single requirement for all queries

Adaptive Scheduling[7]

Update related statistics periodically. Algorithm score

ms is a mean of a statistics of a scheduler mH is mean for historical category H, (maxH-minH) is spread of

values decay reflects the unreliability of the score of algorithms that

have not run for long time.(0 decay < 1)

time is elapse time since ms was updated If quantifier is maximize, zi = zi, otherwize, zi = 1-zi

Adaptive Scheduling[7]

Roulette Wheel strategy◦ Assign each algorithm a slice of a ciurcular

“roulette wheel” with size of the slice being pro-portional to the individual’s score.

Problem of this work◦ How to obtain not-runned schedulers’ statistics.◦ Inaccuracy of the score function

Not runned schedulers for long time 0.5 (due to decay)

Scheduler runs very well 0.5 (since s== H)

Adaptive scheduling[7]

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