The document outlines an end-to-end performance testing setup using Clojure, focusing on a banking simulation system that incorporates Kafka, PostgreSQL, and various services such as transaction and account creation. It details the architecture, including the use of a GraphQL endpoint, message handling, and performance metrics captured during tests. Key tests compare the effects of different Kafka producer settings on system performance, with results indicating the importance of message batching for efficiency.

1. End to end performance
testing with Clojure

2. About me
Gerard Klijs
● @GKlijs
● https://github.com/gklijs
● Java developer with
● Used Kafka several times
● Author of
schema_registry_converter
● Living in Papendrecht

3. Contents
● Demo
● Test setup
● Used libraries
● Results comparing linger.ms 0 and 100
● Questions

4. Bank simulation with end-to-end performance test

6. Overview of the whole system
Every yellow component will be explained in details, and are all but the command
handler only written in Clojure. We use the schema registry for schema
management, also making the messages smaller. All messages will have string as
key and avro as value type.
Meaning of the colors:
● Orange are the Confluent platform parts
● Yellow are the parts of open bank mark
● Green is an NginX instance
● Light blue are PostgreSQL databases

8. Code example start consuming

9. Code example producer

10. Topology
Common dependency of the other parts.
Several functions:
● One way to set the logging for all components.
● All components have knowledge over the topics and data types without
needing to connect.
● Will generate Avro object for (de)serialization.
● Functions wrapping the (Java) Kafka Consumer and Producer.
● Functions for dealing with IBAN and UUID.

12. Synchronizer
Makes sure both the correct topics and schema’s are set.
Checks if it’s possible to set the replication factor to what’s in the config, takes the
minimum of the available nodes and the config.
Note that this has been used only on a clean Kafka cluster, and there is currently
no check for topic properties being correct.

14. Heartbeat
Just a simple producer for easy debugging.
Used a simple message with just a long value.
Exposes and nrepl. A nrepl is a network repl, which can be used to execute code
remotely and get the result back. This is a powerful concept, making it possible to
apply fixes as the code runs, or interactively solve bugs. With the nrepl the pace of
the send messages can be changed.

16. Command generator
Consumes the heartbeats and generates a command for each received heartbeat.
This will be ConfirmAccountCreation first, as it runs there will be less of these. It
rondomly ceates different kinds of ConfirmMoneyTransfer which might fail
because it would cause the balance to become below the limit.

18. Using seancorfield/next.jdbc for PostgreSQL

19. Command handler
Handles the different kinds of command.
● AccountCreationCommand: generates a new iban, if it not already exists
creates a balance using the default values, if it does exists gives back an
AccountCreationFailed.
● ConfirmMoneyTransfer: if the supplied token is correct, and there is enough
money, makes the transfer. Updates both to and form if they are ‘open-bank’
ibans. And creates a BalanceChanged event for each changed balance.

20. GraphQL-endpoint

21. GraphQL-endpoint
Exposes a GraphQL endpoint to make it easy to issue commands and get the
results back in the frontend. All services have there own consumer, and share the
producer and the database.
● Transaction service: makes it possible to query or subscribe to balance
changed events.
● Account creation service: used to create an account. Will link the username
used to log in with the uuid send for the account creation, in order to get the
same iban back should the user log in at another time.
● Money transfer service: tries to transfer money, and provides feedback.

23. GraphQL subscriptions using Lacinia-pedestal

26. Frontend

27. Frontend
The frontend is build on several parts that all end up in a NginX container to be
served.
● The javascript part is build using clojurescript, an important part is the re-
graph library. For clojurescript re-frame is often used, which uses react to
update the dom depending on a global state. Clojurescript is using the Google
Closure compiler to reduce the size of the resulting javascript.
● Bulma is used for the css with just the colors set differently and some
additional animations.
● The output from the tests are added to NginX to make them easily accessible.

29. Running a test
When the test is run it will do several kind of transaction that either increase or
lower the money on the balance in such a way as much goes in as goes out after
10 runs. It measures the time till the new balance comes in.
During the test the load of the system is increased by using the nrepl of the
heartbeat. Increasing the number of heartbeats which in turn will trigger additional
commands to be processed.
Also during the test using lispyclouds/clj-docker-client both the cpu and memory of
parts of the system are measured.
Al the data is written into a file so it can be analyzed later on.

30. Test frontend with etaoin using chrome

31. Using lispyclouds/clj-docker-client for docker

33. Output a test
The generated files can be compared to other files to generate graphs.
All the data is combined, and for each point with the same load some statistics are
calculated. Most often the mean and the standard error.
For different values graphs are generated in the public folder for the frontend so
they can be easily viewed. They are available at the background tab at open-bank.

34. Using kixi/stats to prepare the data

35. Using metasoarous/oz to display using vega

36. Example test, difference linger.ms 0 vs 100
linger.ms is an important setting of the kafka producer. Default is 0 for the client,
but 100 for kafka streams. Instead of 1 message at a time, multiple are send at a
time allowing higher efficiency.
Run on 6-core Macbook Pro with for Docker:
● 4 Cpu
● 12 GiB Memory
● 3 GiB Swap

43. Questions? Code available at open-bank-mark