Memory Issuesin Rails Applications

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Problems of Success (good problems)

Too many users Too much traffic Too much data

Memory Issuesin Rails Applications

Common Problem of Success

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Mobile  SDKs  iOS  &  Android

Web  SDK  RequireJS  &  jQuery

Components  AngularJS

NLP,  etc.  Python

Targe<ng  High-­‐Perf  Java

Analy<cs  Ruby  2.0

Internal  Apps  Ruby  2.0  /  Rails  3

Pub  Portal  Ruby  2.0  /  Rails  3

Ad  Portal  Ruby  2.0  /  Rails  4

Before 1hr @ 4Gb

Before 1hr @ 4Gb

When problems grow faster than the rate at which you can throw HW at them, you actually have to solve them

Before 1hr @ 4Gb

After 5min @ 230Mb

Resolving Memory Issuesin Rails ApplicationsUsing Streams

CSV

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This sucks

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Start thinking here

Memory Leaks

class AddDomainsStep def call(hashes) hashes.map do |hash| transform_and_return(hash) end end end

1 class AddDomainsStep 2 def initialize 3 @domain_config = DomainConfig.instance 4 end 5 6 def call(hashes) 7 hashes.each do |hash| 8 hash['domain'] = 9 @domain_config. 10 domain_for(hash['domain_id']) 11 end 12 end 13 end

1 class DomainConfig 2 include Singleton 3 4 def initialize 5 @domains = {} 6 end 7 8 def domain_for(id) 9 @domains[id] ||= Domain.name_for(id) || '' 10 end 11 end

@domains[id] ||= Domain.name_for(id) || ''

Memory Leak

•Memory that will never be released by the garbage collector.

•Memory usage grows the longer the process runs.

Avoid Global State

•Global variables

•Class variables

•Singletons

•Per-process instance state

Memory Churn

hashes.map do |hash| hash['domain'].downcase.strip end

hashes.each do |hash| hash['domain'].downcase! hash['domain'].strip! end

vs

Memory Churn

•Allocating and deallocating tons of objects slows down processing

•Mutation limits allocations, but makes it easier to introduce bugs

1 hashes.each do |hash| 2 hash['domain'].downcase! 3 hash['domain'].strip! 4 end

Spot the Bug!

# In shared state: @domains[id] ||= Domain.name_for(id) || '' !

# Much later: hash['domain'].downcase! hash['domain'].strip!

Good News!•Allocating and freeing objects is

fairly fast in Ruby •Keeping your stack frame light

will limit the effects of memory churn

Memory Bloat

def to_csv csv = [CSV.generate_line(headers)] !

rows.each do |row| values = headers.map do |header| row[header] || defaults[header] end !

csv << CSV.generate_line(values) end !

csv.join('') end

def to_csv csv = [CSV.generate_line(headers)] !

rows.each do |row| values = headers.map do |header| row[header] || defaults[header] end !

csv << CSV.generate_line(values) end !

csv.join('') end

def to_csv csv = [CSV.generate_line(headers)] !

rows.each do |row| values = headers.map do |header| row[header] || defaults[header] end !

csv << CSV.generate_line(values) end !

csv.join('') end

Memory Bloat

•Memory usage grows with data set

•Loading too much data at once

Laziness

rename_report_fields( squash( add_domains( add_properties( unwind_variations( rows ) ) ) ) )

def duplicate(number, count) if count > 0 [number] + repeat(number, count - 1) else [] end end !

def sum(list) list.inject(0) do |result, number| result + number end end

sum(repeat(5,10)) # => 50

duplicate :: Int -> Int -> [Int] duplicate number count | count <= 0 = [] | otherwise = number:duplicate number (count - 1) !sum :: [Int] -> Int sum [x] = x sum (x:remaining) = x + sum remaining

> sum $ duplicate 5 10 50

Be ProactiveAbout Being Lazy

Enumerable

class AddDomainsStep def initialize(source) @source = source end !

def each @source.each do |hash| hash['domain'] = DomainConfig. instance. domain_for(hash['domain_id']) yield hash end end end

RenameReportFieldsStep.new( SquashStep.new( AddDomainsStep.new( AddPropertiesStep.new( UnwindVariationsStep.new( rows ) ) ) ) )

Buffering