Clojure at a post office
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The document discusses various approaches for handling asynchronous operations when processing a payment for a bill in a Clojure web application. It evaluates 9 different solutions using techniques like synchronous code, promises, core.async, and various Clojure libraries. The top portion provides code snippets for each approach. The bottom compares the performance of synchronous code versus core.async.
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Clojure at a post office
- 1. CLOJURE AT A POST OFFICE
- 3. HTTP-KIT • AWS C1-Medium! • 7GB Ram! • 8 Cores • 313,852 Concurrent Users! • 4756.79 Requests Per Second
- 4. If payment is success: display amount remaining on bill! If payment fails: display error Make a payment on a bill! - Not necessarily a full payment POST /bills/:bill-id/payments Session: user-id Post Data: amount 1. GET credit card token for user! 1.1. POST request to payment gateway! 2. GET how much was left to be payed
- 5. CANDIDATES • Synchronous promises! • Promise monad let/do! • Raw promises! • Raw callbacks! • core.async! • Lamina pipeline! • Meltdown (LMAX Disrupter)! • Pulsar promises! • Pulsar Actors
- 7. SOLUTION 1.1: PROMISE MONAD DO (GET""/bills/:bill*id/payments""[bill*id"user*id"amount]" """""(do'[token"""""""(auth/card/token"user*id)" """"""""""transaction"(payment/bill"bill*id"amount"token)" """"""""""details"""""(bill/details"bill*id)]" """""""""(return" """""""""""(if'(success?"transaction)" """""""""""""(render/remaining/response"details"amount)" """""""""""""error*response))))
- 8. SOLUTION 1.2: PROMISE MONAD LET/DO (GET""/bills/:bill*id/payments""[bill*id"user*id"amount]" """""(let'[token*req"""(auth/card/token"user*id)" """""""""""details*req"(bill/details"bill*id)]" """""""(do'[token"""""""token*req" """"""""""""transaction"(payment/bill"bill*id"amount"token)" """"""""""""details"""""details*req]" """""""""""(return" """""""""""""(if'(success?"transaction)" """""""""""""""(render/remaining/response"details"amount)" """""""""""""""error*response)))))
- 9. SOLUTION 1.3: PROMISE MONAD LET/DO/DO (GET""/bills/:bill*id/payments""[bill*id"user*id"amount]" """""(let'[token*req"""(auth/card/token"user*id)" """""""""""details*req"(bill/details"bill*id)]" """""""(do'[token"""""""token*req" """"""""""""transaction"(payment/bill"bill*id"amount"token)]" """""""""""(if'(success?"transaction)" """""""""""""(do'[details"details*req]" """""""""""""""""(return"(render/remaining/response"details"amount)))" """""""""""""(return"error*response)))))
- 21. CQRS! • Want fast reads. Reduce the number of queries.! • Don't want to have to update write code every time we add a new reader.! • Don't want to have to update reader every time there's a new writer.! • Would be great to have an event stream to re-calculate current state.
- 22. 1.#Just#write#to#normalised#copy# 1.1.# Just#read#everything#every#time# 1.2.# Read#and#cache# 1.2.1.# Cache#the#page# 1.2.2.# Cache#the#intermediate#data;structure# 2.#Just#write#to#views# 2.1.# Direct#write# 2.2.# Event#stream# 2.2.1.# Persisted# 2.2.1.1.# Domain#events# 2.2.1.1.1.#Live#update# 2.2.1.1.2.#Async#update# 2.2.1.2.# CRUD#event# 2.2.1.2.1.#Live#update# 2.2.1.2.2.#Async#update# 2.2.2.# Ephemeral# 2.2.2.1.# Domain#events# 2.2.2.1.1.#Live#update# 2.2.2.2.# CRUD#event# 2.2.2.2.1.#Live#update# 3.#Write#to#views#and#normalized#copy## 3.1.# Direct#write# 3.2.# Event#stream# 3.2.1.# Persisted# 3.2.1.1.# Domain#events# 3.2.1.1.1.#Live#update# 3.2.1.1.2.#Async#update# 3.2.1.2.# CRUD#event# 3.2.1.2.1.#Live#update# 3.2.1.2.2.#Async#update# 3.2.2.# Ephemeral# 3.2.2.1.# Domain#events# 3.2.2.1.1.#Live#update# 3.2.2.2.# CRUD#event# 3.2.2.2.1.#Live#update# 3.3.# Write#to#normalized#keyspace#causing# trigger# 3.3.1.# Direct#update#to#views# 3.3.2.# Event#to#be#published# 3.3.2.1.# Persisted# 3.3.2.1.1.#Live#Update# 3.3.2.1.2.#Async#update# 3.3.2.2.# Ephemeral# 3.3.2.2.1.#Live#Update
- 23. Write ! ! Cassandra Service A Service B Index Maintainer Notify Read Write Rabbit MQ Publish Triggers
- 24. CASSANDRATRIGGERS • Can just throw the Clojure jar in there! • Everything is byte buffers! • Need to know the type of fields out of band! • One class per trigger per table! • Bizarre key names (format changes depending on value type)