Typical development problems and mistakes

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Timothy N. Tsvetkov2011, rubyc, Kiev

Evil Martians

Air and live

Genres

Personal playlists

REN TVis

The best Online TVin

Russia

Architecture

Planning

• We have planned API to develop

• CDN Video have planned API to develop

Real life

• CDN Video API changed

DDs

• BDD

• TDD

• CI

• ADD

• DDD

• ASP .NET MVC 1.0

Truth

• BDD — Body Dysmorphic Disorder

• TDD — Test Driven Development

• CI — Convergence insufficiency

• ADD — Attention Deficit Disorder

• DDD — DDD

Testing limitations

• We can’t test everything

• You can’t develop an algorithm to proof that your program is correct

• Testing is hard

• Tests have errors

• Not that effective at finding bugs

Race conditions

• Most developers don’t think about race conditions

• Validates uniqueness is not race conditions safe

• Some gems are not race conditions safe and it is your business to check them

Optimistic locking

• Each update to the record increments the lock_version column and the locking facilities ensure that the records instantiated twice will let the last one saved raise a StaleObjectError if the first was also updated

• Doesn’t work between actions like edit/update

Pessimistic locking

• SELECT FOR UPDATE

• FOR UPDATE causes the rows retrieved for by the SELECT statement to be locked as thought for update. This prevents them from being modified or deleted by other transactions until the current transaction ends

Advisory lock

• Locks that have application defined meanings

Advisory locks. Usage

Test on race conditions

• It is hard to find them and there is no tool for that

• You can use test hooks in your production code for testing them in your rspec

Deamons

• Erlang is great

• Node.js sucks

Deamons v. 1

• Rebar to install debs, compile and start

• Classical OTP: Supervisor + fetchers, monitors

Deamons v. 2

• Supervisors spawns workers

• Workers spawn fetchers and monitors them

• Worker never die

Deamons v. 3

• v. 1 without Rebar but with Runit

Investigate a problem

• Log everything you can

• strace, tcp dump, netcat, gdb

• etc

Special thankstoYaroslav Markin

Dumb questions