The intent of the previous concatenation was to minimize object
allocations, which can end up being a slow killer. However, it turns
out that under MRI 2.4.x, the shove-strings-in-an-array-and-join method
is not only arguably more common but (in this particular case) actually
allocates *fewer* objects than the string concatenation.
Or, at least, that's what I gather by running this:
words = %w(palmettoes nudged hibernation bullish stockade's tightened Hades
Dixie's formalize superego's commissaries Zappa's viceroy's apothecaries
tablespoonful's barons Chennai tollgate ticked expands)
a = Account.first
KeywordMute.transaction do
words.each { |w| KeywordMute.create!(keyword: w, account: a) }
GC.start
s1 = GC.stat
re = String.new.tap do |str|
scoped = KeywordMute.where(account: a)
keywords = scoped.select(:id, :keyword)
count = scoped.count
keywords.find_each.with_index do |kw, index|
str << Regexp.escape(kw.keyword.strip)
str << '|' if index < count - 1
end
end
s2 = GC.stat
puts s1.inspect, s2.inspect
raise ActiveRecord::Rollback
end
vs this:
words = %w( palmettoes nudged hibernation bullish stockade's tightened Hades Dixie's
formalize superego's commissaries Zappa's viceroy's apothecaries tablespoonful's
barons Chennai tollgate ticked expands
)
a = Account.first
KeywordMute.transaction do
words.each { |w| KeywordMute.create!(keyword: w, account: a) }
GC.start
s1 = GC.stat
re = [].tap do |arr|
KeywordMute.where(account: a).select(:keyword, :id).find_each do |m|
arr << Regexp.escape(m.keyword.strip)
end
end.join('|')
s2 = GC.stat
puts s1.inspect, s2.inspect
raise ActiveRecord::Rollback
end
Using rails r, here is a comparison of the total_allocated_objects and
malloc_increase_bytes GC stat data:
total_allocated_objects malloc_increase_bytes
string concat 3200241 -> 3201428 (+1187) 1176 -> 45216 (44040)
array join 3200380 -> 3201299 (+919) 1176 -> 36448 (35272)
aa57929688