GoRuCo 2011 | Gordon Diggs

Ryan Smith (@ryandotsmith)

Gene Amdahl's Law
How to improve concurrency
- Removing FIFO
  - FIFO isn't really needed a lot of the time in a queue of jobs
    - can ditch FIFO if order of jobs doesn't matter
    - if order matters, have a job fire things that depend on it at completion
  - fuzzy-FIFO
    - have many head nodes with a top boundary
    - worker can take job from any head node above top boundary
  - lock_head() (PL/pgSQL) EXECUTE 'SELECT id FROM' || ' jobs' || ' WHERE locked_at IS NULL' || ' ORDER BY id ASC' || ' LIMIT 1' || ' OFFSET' || relative_top || ' FOR UPDATE' || ' NOWAIT' INTO locked;
    - do this procedure with a spin lock
    - skip lock ?
  - MVCC
- Relax constraints
github.com/ryandotsmith/queue_classic
- dependencies
  1. pg gem
  2. json
- faster b/c it doesn't make a lot of object

Code needs to work today just once, and be easy to change forever
The purpose of design is to reduce the cost of change
Simple ways to judge the goodness of code
- Transparent - the consesquences of change are visible and predictable
- Reasonalbe - the cost of adding a new feature is proportional to its value
- Usable - if you wrote it, you can reuse it
- Exemplary - More code like this would be good for your app
Code will never be done, just need to know when to stop
Slides: less-goruco.heroku.com
Don't guess what changes will come, just guess what will change.
Let objects stand free

SQL Operators
- Bulk inserts incredibly faster than regular inserts
- HAVING count(1) > 1
- Pagination
  - SELECT SQL_CALC_FOUND ROWS * FROM people WHERE face = 'awesome' LIMIT 10 OFFSET 20;
  - SELECT FOUND_ROWS();
slim_scrooge github.com/sdskyes/slim_scrooge
- Learns to select only what's necessary
- Uses a lot of memory for bigger apps
String Operators: strlen, left, right, concat, reverse
DB regex: SELECT 'John' REGEXP '^[a-zA-Z]+$';
Think about setting max lengths for fields - could save a lot of space at scale
validates_uniqueness_of doesn't work.
- :unique is property of index, not column
github.com/seejohnrun/database_validation
ENUMs - kind of like validates_inclusion_of
- pg adapter doesn't absoultely support - but gems exist to do so
Single Table Inheritance
- if subclasses differ only in behavior, ok
- otherwise, use Class-Table Inheritance
  - Superclass table stores common attributes
  - Not supported by ActiveRecord