Created
November 12, 2012 22:09
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# Another attempt using the built in Rails.cache.fetch (better serialization/deserialization) | |
class ActiveSupport::Cache::DalliStore | |
def fast_fetch(name, options=nil) | |
options ||= {} | |
name = expanded_key name | |
dupe_name = name+'_dupe' | |
if block_given? | |
unless options[:force] | |
entry = instrument(:read, name, options) do |payload| | |
payload[:super_operation] = :fetch if payload | |
read_entry(name, options) | |
end | |
end | |
if !entry.nil? | |
instrument(:fetch_hit, name, options) { |payload| } | |
entry | |
else | |
Thread.new do | |
result = instrument(:generate, name, options) do |payload| | |
yield | |
end | |
write(name, result, options) | |
write(dupe_name, result) | |
end | |
puts 'using old value' | |
read(dupe_name) | |
end | |
else | |
read(name, options) | |
end | |
end | |
end |
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# This is an alternative using redis, but it doesn't serialize/deserialize like Rails.cache | |
class Redis | |
def fetch key, options=nil | |
options ||= {expires_in: 10.minutes} | |
key_expires = key + '_expires' | |
entry = get(key) | |
expires = Time.parse(get(key_expires)) rescue 1.second.ago | |
if expires < Time.now | |
if entry.nil? | |
p 'update in real time' | |
new_entry = yield | |
set key, new_entry | |
set key_expires, options[:expires_in].from_now | |
new_entry | |
else | |
Thread.new do | |
p 'update in background thread' | |
new_entry = yield | |
set key, new_entry | |
set key_expires, options[:expires_in].from_now | |
end | |
set key_expires, 10.seconds.from_now # similar to :race_condition_ttl | |
entry | |
end | |
else | |
entry | |
end | |
end | |
end |
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irb(main):612:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
"update in real time" | |
=> "2012-11-12 14:03:26 -0800" | |
irb(main):612:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
=> "2012-11-12 14:03:26 -0800" | |
irb(main):612:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
=> "2012-11-12 14:03:26 -0800" | |
irb(main):613:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
"update in background thread" | |
=> "2012-11-12 14:03:26 -0800" | |
irb(main):612:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
=> "2012-11-12 14:03:26 -0800" | |
irb(main):614:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
=> "2012-11-12 14:03:33 -0800" | |
irb(main):615:0> REDIS.fetch('test', :expires_in => 6){ sleep 1; Time.now } | |
=> "2012-11-12 14:03:33 -0800" | |
irb(main):620:0> | |
# the first line where it says "update in real time" is the only one that takes 1 second to return |
Just want to say, this is GREAT I've been searching around for a couple weeks for anyone else doing this, and I'm really surprised to see nothing out there! Thanks for the snippet :)
Also, I made a simple fork adding YAML serialization and race_condition_ttl to the redis adapter here: https://gist.github.com/kyletns/224c37c0202f71423e95
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This is my first crack at it - it seems a little inefficient because it needs to set 2 keys in redis. If anyone has a way to improve it let me know!