Convincing developers to write tests for new code is hard; convincing developers to write tests for new event data is even harder. At Reddit, engineers have often deployed new app versions, only to find out later that the event wasn’t firing at all, or it was missing critical fields. So this begs the question, “How can engineers at Reddit be confident that the events they instrument are accurate and complete?” In this session, we will learn about an internal tool developed at Reddit to QA events in real-time. This KSQL-powered web app streams events from our pipeline, allowing developers to filter events they care about using criteria like User ID, Device ID or the type of user interaction. With a backbone of KSQL and Kafka Streams, engineers can get real-time feedback on how accurate (or how erroneous) their event data is.

1. Live Event Debugging With
kSQLdb at Reddit
Hannah Hagen, Paul Kiernan
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2. 2023

3. Release new
feature
The Old Testing Process
QA
(fires events)
WAIT 2
HOURS
Query the data
warehouse

4. Drawback
of 2 hour
delay
➔ Testing was not coupled with
development

5. What we
really
wanted
(and
didn’t
have)
➔ Quick and efficient testing
procedure (no delays!)
➔ No prior knowledge required (e.g.
how to access our data
warehouse, etc)
➔ In summary, we wanted to
remove the barriers to test event
data.

6. Why
kSQLdb?
➔ Real-time event stream
➔ We already had Kafka-based
infrastructure.
➔ Easy set up. Just need to run a
few “create stream” and “create
table” statements and deploy a
kSQLdb cluster.
➔ SQL-like filters meant developers
can search for the event type or
the testing session they care
about.

7. 2023
Live Event
Debugger

8. 2023
Live Event
Debugger

9. 2023
Live Event
Debugger

10. 2023
Live Event
Debugger

11. 2023
Live Event
Debugger

12. 2023
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13. 2023
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15. End Result
➔ Couple seconds delay between
firing event and seeing it in Web
UI
➔ UI-driven QA lows barriers for
testing event data

16. 2023
Thank You
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