Improving throughput with the Theory of Constraints and Queuing Theory

Improving throughput
with the
Theory of Constraints
and
Queuing Theory
www.journey-to-better.com

Aims of this presentation
For each theory:
1.Explain it in simple terms
2.Show practical application

Theory of Constraints

Theory of Constraints (TOC)
Idea
Process
A
Process
B
Process
C
Customer
Where should we strive
to increase throughput?

Idea
Process
A
Process
B
Process
C
Customer
Where should we strive
to increase throughput?
5 units
Per week
2 units
Per week
3 units
Per week

"a chain is no stronger than its
weakest link“
Improving strong links, does not
strength the chain.
To achieve more of your goal,
improve your weakest link.

1. Identify the constraint
2. Exploit the constraint
3. Subordinate all else
4. Elevate the constraint
5. Repeat
Five Focusing Steps
Get the most out of the constraint,
with only minor changes.
Major changes to the constraint,
Including increasing capacity.

Practical TOC
We are going to:
1. Map team workflow to Task Board
2. Populate the board
3. Run the system
4. Use TOC to increase throughput

Backlog Analysis & Plan Coding Review Testing Accept Done
Map team workflow

Populate with current state

Constraint: The resource or policy that
prevents the organization from obtaining more
of the goal.
Symptoms
• Work piles up waiting to be processed by the
constraint.
• Resource is heavily stressed.
• Resources downstream from constraint are
regularly idle.

Doing Ready
Split Testing column

Doing ReadyDoing ReadyDoing ReadyDoing Ready
Split all other columns

Get the most capacity out of the constrained
process, with only minor changes
Some options:
• Shield them from interruptions.
• Limit their WIP.
• Reduce their non value add work.
Note: Do not ask them to do overtime.

(5)
Exploit the constraint
Limit WIP in Testing

(5)
Let it run
Constraint remains

Align the whole system or organization to
support the decisions made above.
Some options:
• Limit WIP of upstream to match.
• Upstream do preparation work.
• Upstream improve their quality.
• Pair upstream with constraint staff.

(5)(5)(5)(5)
Subordinate all else
Match upstream WIP to constraint
Devs do more test prep work.
Dev-QA pairing

(5)(5)(5)(5)
Let it run
Constraint remains

Make other major changes needed to break the
constraint. A.k.a. Enhance the capability of the
constraint to increases its throughput further.
Some options:
• Improve their tools.
• Improve their environment.
• Improve their team work.
• Hire more people.
Why do we not do this first?

(5)(5)(5)(5)
Elevate the constraint
Improve tools (reduce manual effort)
Get Devs to help execute tests
Hire another tester

(5)(5)(5)(5)
Let it run
Constraint has been broken

5. Repeat
• The bottleneck should now have shifted.
• Start all over again

To increase throughput
apply the Five Focusing Steps:
5. Repeat
Summary – Theory of Constraints
Minor changes
Large changes

Queuing Theory

Queuing Theory
Began by answering the question:
How many phone lines will the Copenhagen
Telephone exchange need to handle peak
load?
Paper published by Agner Krarup Erlang in
1909

Serious math
Not for today

Simple principles
To increase throughput:
• Reduce utilisation
• Reduce batch size
• Reduce item size

Why reduce utilisation
Queuing Theory says that in a system with variability,
increased resource utilisation leads to an increase in cycle
time.
Software development has lots of variability.
Past a tipping point the increase in cycle time is exponential.

Tipping point
Utilisation0 100
CycleTime
Tipping Point
Some examples:
• Computer CPU
• Network Router
• Building Fire Exit
• Road

Tipping Point in action
Utilisation above the capacity of the road,
(just one more car),
created unevenness,
created delays,
greatly increased cycle time.

Why reduce batch size?
• Littles Law is part of Queuing Theory
Avg. Cycle Time =
Work In Progress (WIP)
Avg. Throughput Rate
Throughput
Cycle
Time
WIP
Batch Size

Why reduce item size?
Large items take longer to process,
leading to:
• Queues (extra WIP)
• Variability (the bad kind)

Exercise – Improve highway throughput
Image: https://www.flickr.com/photos/thienzieyung/

Highway - Reduce Utilisation
Q: How would we reduce utilisation?
A: Announce blockage radio & signs.
Image: https://www.flickr.com/photos/highwaysagency/

Highway - Reduce Batch Size
Q: How would we reduce batch size?
Image: https://www.flickr.com/photos/29233640@N07/

Highway - Reduce Item Size
Q: How would we reduce item size?
Image: https://www.flickr.com/photos/null0/
A: Replace Trucks with Cars, Cars with Motorcycles.

The good news
Queuing Theory is already built into:
• agile
• Scrum
• Kanban

Queuing Theory in agile
How does agile lower Utilization?
• Promoting sustainable development.
• Customer collaboration.
How does agile lower Batch Size?
• Focus on early delivery of Working Software.
How does agile lower Item Size?
• Focus on business feedback & simplicity.
Image: http://www.agilemanifesto.org/

Queuing Theory in Scrum
How does Scrum lower Utilization?
• Team members 100% allocated.
• Team pulls in work to sprint.
How does Scrum lower Batch Size?
• Sprint length.
How does Scrum lower Item Size?
• Time boxing & D.O.D. encourage
splitting items.

Queuing Theory in Kanban
How does Kanban lower Utilization?
• Pull approach.
• Limiting WIP.
How does Kanban lower Batch size?
• Limiting input queues.
How does Kanban lower Item size?
• Building a dry stone wall approach…
Image: https://www.flickr.com/photos/bods/

To increase throughput:
Lower
Utilisation
Work on
smaller batches
Work on
smaller items
Summary – Queuing Theory

Contact Details
Twitter @andrewrusling
Blog www.journey-to-better.com
SlideShare www.slideshare.net/andrewrusling
E-mail andrewrusling@hotmail.com
Google+ +AndrewRusling

Improving throughput with the Theory of Constraints and Queuing Theory

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