Performance tips

[joshmfrankel]

Db

• avoid plucking ids/select ids instead
• only select what you need
• ar is lazy eval use this to build sql
• always filter with where clause
• arel tables for complexity
• indexes
• explain analyze
• a single query is generally faster than multiple

ruby

• only iterate collections once if possible
• memorize expensive logic
• write conditionals least expensive first including compound and if elsif
• hashmap for lookups
• Avoid using sleep
• watch for n+1 style code
• benchmark with big data
• eager load to avoid n+1
• find_in_batches to avoid loading all into memory etc
• .exists? > .any? > .present? for ActiveRecord collections
• .any? / .one? vs .all? / .none?

Jobs

• Collection All > One job standard to defer multiple processing
• Async for non-critical operations
• Only retry if not doing so would cause problems

tests

• don't create when you can build
• group test setup with like tests
• unit > integration > feature
• request specs with Capybara
• Stub external systems
• Don't make http calls

js

• debounce or throttle expensive events
• memoize