No one likes getting up at 3 am to fix bugs OR how to be a better developer

Copyright © 2017, Lima Lima Charlie, LLC. All rights
reserved.
No One Likes Getting Up at
3AM to Fix Bugs
~ Or ~
How to be a Better Developer
Rob Grzywinski

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About Me -- Rob Grzywinski
◉ Writing software professionally >20y
◉ Chief Technology Officer
◉ Advisor to Silicon Valley and other Companies
Big Data & Analytics
Artificial Intelligence
Data-Centric Apps
◉ Multiple successful startup acquisitions
Latest: Aggregate Knowledge (AdTech) for >$100M (USD)

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No rule is Black and White …
… Including this one

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Lesson #1
The worst happens when you’re the least ready for it!
1

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Am I going to understand this:
◉ At 3AM ?
◉ With a Hangover ??
◉ After eating bad McDonald’s fries ???
(Cuz that’s when you’re going to need it!)
Mantra
(Copyright WarnerBros)
Friends don’t let friends Code Drunk!

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Code spends the majority of its lifetime
in maintenance. Write code so that it
can be maintained!
!

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3AM is for Sleeping!
How can you write software so that you never get the
3AM call to fix it?
But if you are woken up, will you have everything you
will need to fix it?

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◉Naming (to name it you have to understand it)
◉Formatting (pick a style and follow it)
◉Documentation (sufficient useful supporting docs)
Things to Think About

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Lesson #2
You’re not even half as smart as you think you are!
2

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If you’re making something up ...
… you’re probably doing it wrong!
Look for standard answers to problems
◉ Easier to Debug
◉ Likely handles cases you haven’t thought of
◉ Provides on-line references, support, etc
Don’t Make It Up!

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Oh! The Horror!
WITH
interval_window AS (
SELECT reading_date
, DATETIME_DIFF(LEAD(reading_date) OVER (ORDER BY reading_date), reading_date, SECOND) AS next_interval
, DATETIME_DIFF(reading_date, LAG(reading_date) OVER (ORDER BY reading_date), SECOND) AS prev_interval
FROM latest_meter_data
)
, meter_data_with_boundaries AS (
SELECT reading_date
, CASE
WHEN (next_interval = 900) AND (prev_interval > 900 OR prev_interval IS NULL) THEN 'START'
WHEN (next_interval > 900 OR next_interval IS NULL) AND (prev_interval = 900) THEN 'END'
WHEN (next_interval IS NULL OR next_interval > 900) AND (prev_interval > 900 OR prev_interval IS NULL) THEN 'START-END'
ELSE NULL
END as boundary
FROM interval_window
)
, meter_data_boundaries AS (
SELECT reading_date, boundary
FROM meter_data_with_boundaries
WHERE boundary IS NOT NULL
)
, almost_islands AS (
SELECT reading_date
, boundary
, LEAD(reading_date) OVER(ORDER BY reading_date) AS next_date
, LEAD(boundary) OVER(ORDER BY reading_date)
FROM meter_data_boundaries
)
, islands AS (
SELECT reading_date as start_date
, CASE
WHEN boundary = 'START-END' THEN reading_date
ELSE next_date
END as end_date
FROM almost_islands
WHERE boundary LIKE 'START%'
)
(40+ lines and doesn’t work)

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Standard Answer
WITH
sequence_offsets AS (
SELECT reading_datetime
, (RANK() OVER(ORDER BY reading_datetime) *
duration) AS offset_seconds
FROM sensor_interval_data
)
, islands AS (
SELECT MIN(reading_datetime) AS start_date
, MAX(reading_datetime) AS end_date
FROM sequence_offsets
GROUP BY DATETIME_SUB(reading_date,
INTERVAL offset_seconds SECOND)
)
(10 lines and covers corner cases)

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Gotchas
◉ Dates4 (use a library!)
◉ Timezones4 (you’re going to screw it up! Trust me)
◉ Off-by-One (write it out to make sure you have it & test!)
◉ Wildcards (always have backups :) )

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Testing
“I don’t write buggy software so why should I test?!?”
3

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“Testing cannot show the absence
of defects, it can only show that
software defects are present”
- Robert Pressman
“

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Positive Testing
isValidUser(String username):Boolean
Valid users: “Bob” and “Alice”
Test: “Bob” ➞ true
Test: “Alice” ➞ true
Works!

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Not-so-Positive Testing
isValidUser(String username):Boolean
Valid users: “Bob” and “Alice”
Test: “Joe” ➞ true
Test: “Lucy” ➞ true
Works! Maybe Not!?!

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Negative Testing
isValidUser(String username):Boolean {
return true;
}
Whoops!

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Confirmation Bias
The tendency to search for, interpret, favor, and recall
information in a way that confirms one's preexisting
beliefs or hypotheses2

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Code Coverage
◉ Does 90% code coverage by tests mean that you
miss 10% of the defects?
◉ Does 100% code coverage mean that you
miss 0% of the defects?

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100% Code Coverage
isValidUser(String username):Boolean {
return true;
}
Test: “Bob” ➞ true
Test: “Alice” ➞ true
200% Code Coverage != 0 defects!

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Testing
Think of testing like trying to lose weight:
◉ You don't try to lose weight by weighing yourself
more often
◉ What you eat before you step onto the scale
determines how much you will weigh

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Testing
You don't improve software quality by increasing the
amount of testing
To improve your software, don't test more:
Develop Better!1

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Instead of writing tests
Assert things you know!
assert3:
● state a fact or belief confidently and forcefully
● cause others to recognize (one's authority or a right) by confident and forceful behavior
Assert not Test!

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What Should I Focus On?
“How do I accelerate my career?”
3

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“Practice does not make perfect.
Only perfect practice makes perfect.”
- Vince Lombardi
“

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Which Technology Should I Try?
Doesn’t matter but here are some options:
◉D3 (do something hard!)
◉SQL (really learn it -- CTEs, Window Functions, etc.)
◉RegEx (really, really learn it)
?

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What Should I Do?
Pick anything and:
◉Take it apart
◉Learn how it works (remember 3AM?)
◉Fix a bug and submit PR
?

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Absolute Musts!
◉IDE (learn it without the mouse)
◉Debugger (print statements are for babies :) )
◉Cloud Anything (spin up, do something, tear down)
◉Async / Threading (race conditions, debugging, etc.)

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Open Source
“What should I be worried about?”
4

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There’s a zillion libraries to do anything:
◉What is the license? (no GPL!)
◉When was the last release?
◉Do bugs get fixed? (How often? By whom?)
◉Community? (StackOverflow, etc)
Which Library?!??

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Anything Else?
Always explicitly manage your dependencies
(Know when the world moves underneath you)
?

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Any questions ?
You can find me at:
◉ rob@limalimacharlie.com
Thanks!

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Appendixn

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1. http://cc2e.com/ (Code Complete by Steve McConnell)
2. https://en.wikipedia.org/wiki/Confirmation_bias
3. https://www.google.com/search?q=define%3A+assert
4. http://revelry.co/time-zone-bugs/
References

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Attribution
1.http://www.slidescarnival.com/

No one likes getting up at 3 am to fix bugs OR how to be a better developer

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