CONTEXTVS, STVLTE!
Context, stupid!
Piotr Przybył
piotr[at]przybyl.org
piotrprz
WrocławJUG, 20 III MMXVIII
© 2018 Piotr Przybył. Licensed under Simplified BSD license.
CAVEAT AVDITORES
Context exists.
Go and find it.
Don't guess it.
169
Is this far?
https://en.wikipedia.org/wiki/File:Mars_Climate_Orbiter_-_mishap_diagram.png
https://photojournal.jpl.nasa.gov/catalog/?IDNumber=PIA02330
Skipping the context
can be expensive.
Sometimes very much.
What is the speed of light?
~3 x 108 m/s
in vacuum
90 m/s less in the air
~1.2 x 108 m/s in diamonds
Make sure your mantra
matches the context.
Sometimes you can't alter
your context.
Context can live long.
Very long.
https://upload.wikimedia.org/wikipedia/commons/8/8c/PC-Speaker_IMG_9311-9312.JPG
Hello! :-)
Привет! )))
Salut ! :-)
Cultural context matters.
It is in us.
Your users have one.
You have one too.
Sometimes context is FUBAR!
Context in not only
input to your system.
Desired effect
makes your context too.
Which sorting algorithm is the best/fastest?
I IV II III
1 4 2 3
bubble: 5 comparisons
quick: 6 comparisons
Check: https://visualgo.net
Factors
- initial order
- keeping initial order
- data set size
- cost of comparison
- cost of swap
- cost of insertion
- cost of index based access
- cost of additional memory
- etc.
There is no
"the best [sorting] algorithm"
if the data is unknown.
The data is your context.
Slow app
Slow DB?
Indexes to the rescue??
Indexes
- used in WHERE clause
- build and balanced during INSERTS*
- make sense for fairly distributed values
- "easy" to index
Indexes are not free lunch.
Gluttony is not healthy.
Ingredients matter.
The way you process data
is your context.
Print sorted list
of children's names
in typical 3 tier web application
ADAM ANNA HVBERT
ADAM ANNA HVBERT
ORDER BY is not for free.
Neither is any other data processing.
The purpose of data processing is your context.
Optimisation
Make sure that
what you define your context
is not too narrow.
Interrupt in Java is broken
because it doesn't stop the thread instantly, you need some ceremony, so always `interrupt` your Thread again.
https://docs.oracle.com/javase/tutorial/essential/concurrency/interrupt.html
An interrupt is an indication to a thread that it should stop what it is doing and do something else. It's up to the programmer to decide exactly how a thread responds to an interrupt, but it is very common for the thread to terminate. This is the usage emphasized in this lesson.
in other words
interrupt means
May I have your attention, please?
Thread.interrupt is not a drop-in replacement for
Thread.stop
Thread.destroy
Transactions are a must
for any serious system
to keep data consistency
Are they really?
TransactionlessTransactions across REST microservices?
What is the most accepted transaction strategy for microservices
How I Avoid Two-Phase Commit
When demanding transactions
make sure you don't do too much
Composition good, inheritance not good
[...] general principle in type system design: It is safe to assume that a type T is a subtype of a type U if you can substitute a value of type T wherever a value of type U is required. This is called the Liskov Substitution Principle.
The principle holds if T supports the same operations as U, and all of T's operations require less and provide more than the corresponding operations in U.
Programming in Scala by M. Odersky, L. Spoon, B. Venners
Inheritance isn't bad per se.
Misunderstanding and misusing it is bad.
Composition vs. Inheritance: How to Choose?DRY vs. DAMP
DRY vs. DAMP
It's a balance, not a contradiction
Simple way of finding and determining context
Why?
Why?
Why?
Why?
Why?
A bit more advanced
Fishikawa
Ishikawa fishbone diagrams
A.K.A. Cause-and-effect diagram
CONTEXTVS, STVLTE!!
Thanks a lot.
Be aware!
Because it depends!!
Piotr Przybył
piotr[at]przybyl.org
piotrprz
WrocławJUG, 20 III MMXVIII
http://bit.ly/2GDNuBk
