How to Pass the Apache Cassandra Developer Exam (for Free!) in 2021

For a limited time, you may try (and retry) DataStax Academy’s Cassandra Developer exam for free, and get a valuable Apache Cassandra Developer Associate certification. Here is all about these newly reviewed certification and exam, including some practice tests I recommend to improve your chances and score higher.

About the Cassandra Developer Certification

DataStax is the largest distributor of a commercial version for Apache Cassandra. Its DataStax Enterprise (DSE) includes core open source Cassandra, and it is free for developers working on smaller workloads. The new DataStax Astra is a cloud version you may try for free as well.

DataStax offered Cassandra Developer exams and certifications for years. In mid-2020, with the reviewed Dev and Admin certifications for Cassandra 3 and DataStax Enterprise 6, they also changed their proctored provider to Mercer Mettl, a small firm from India.

The price for a Cassandra Developer exam used to be $300 US or more. Right now, the listed price is at $145 US. But DataStax is running a huge special, that can help you pass this exam for free. Here is how…

About the Developer Path Courses

• They call “Developer Path” three DataStax Academy courses that you must watch, to be able to ask for a free voucher, and try pass the Cassandra Developer exam for free. The courses are in fact several hours long videos, with quizzes and labs that require practicing by yourself, on your own installation of Cassandra:
  • DS101 – Introduction (30 minutes).
  • DS201 – Foundations (6 hours), mostly about Architecture.
  • DS220 – Data Modeling (12 hours), including CQL (Cassandra Query Language).
• You cannot watch their videos in high-speed, at your own pace. But they published them as well on YouTube. You’ll still have to zip-zip through their on-site videos, to mark each segment “complete”.
• Quizzes are great to quickly check if you properly understood the last video segment, but don’t rely on their format for the exam: the Cassandra Developer exam questions are more elaborate and scenario-like, with no True/False or multiple-select choices. Quizzes must be also completed for the Dev path, with a score decent enough (don’t worry, they do not expect it 100%).
• Labs may help of course, but they are not required for the exam. They also use a KillrVideo sample that you don’t need to remember for the exam. If you do not have time enough, or if you don’t have a computer powerful enough to support their use cases, you can stick to the theory and this could do it. Nobody will care or ask you if you bothered to install and play with Cassandra for real. In fact, their total time includes hours you might have to spend on these labs.
• Once you complete these courses, send an email to [email protected] and ask them for a free voucher. They will send you a coupon code in no time. You may use it to try the Cassandra Developer exam for free for the first time, or even to retry it again if you fail once! Here is how your dashboard should look once you complete all courses:

About the Cassandra Developer Exam

• No need to schedule the exam, because there are proctors online anytime 24/7. I passed my Cassandra Developer exam in a Sunday at noon, when it felt right.
• Start the exam from your Mettl dashboard. When asked for a payment, enter your coupon code (if you have one) and you’re no longer sent to PayPal. Otherwise, the exam costs $145 US.
• The proctored exam is through a Chrome add-on that will take over your screen, with your consent.
• Connectivity was smooth enough for me, and the proctor nice, not many questions asked (just a 360 degrees tour of my empty desk with laptop’s camera).
• They take your picture and need a photo ID. This was harder for me, as I tried 5 times and it was still blur. After which they asked me to scan it (with the cellphone) and send them the picture by email.
• The exam will start right away after. There are a total of 60 questions, all single-select with four choices each. No True/False or multiple-select questions. More than half are scenario-based, with either CQL statements or some data modeling on real life examples. You have 90 minutes max, that could go fast because of the large number of questions. Find your pace and don’t waste too much time on them: better mark for later review any question for which you have doubts. You could start feeling a bit exhausted midway through, but just keep going.
• The passing score is 70%. This means you can get max 18 questions wrong. It may look easy, but it is not: many questions are tricky, problem-solving, touching multiple aspects, and it is easy to miss a point. If you leave for review the questions you’re not sure about, this will give you a nice estimate by the end if you’re good or not.
• You may get an email right away after you finish the exam: they will tell you if you failed or passed, and with what score. If you passed, you’ll find a verification link in your Mercer Mettl dashboard, with your Cassandra Developer exam sheet (they don’t tell you which questions you got wrong). You may download your certificate in PDF format as well, here is mine:

What the Developer Exam Covered (or not)

Things you absolutely need to know for the actual exam:

• Chebotko diagrams – that’s a must. With access patterns in application workflow diagrams.
• Keys, keys, keys – learning EVERYTHING about the primary, partition and clustering keys. You’ll be asked to determine primary keys, recognize primary keys from Chebotko diagrams, identify them from access patterns, filter by primary keys, define them in CREATE TABLE etc etc.
• Multi-row partitions – when a query may return a row, a partition, multiple rows from one or multiple partitions. Make sure you properly understand that by adding clustering keys, you likely switch to a multi-row partition.
• CQL CRUD operations – understand “upserts” with INSERT or UPDATE, and how they work (or not) in applied/unapplied batches, or as lightweight transactions.
• read/write techniques – lightweight transactions, batches, secondary indexes, materialized views – what they are, how to properly define them or use them, and when to use them (or not).
• date/time and GUID data types – in particular date vs timestamp, and UUID vs TIMEUUID.
• STATIC – can be tricky and you may miss it from a table definition, be aware.
• RF and CL – typical scenarios with replication factor (RF) per data center, and R/W operations with specific consistency level (CL). Including the linearizable consistency!

Things I didn’t really expect in the exam:

• DSBulk – this is a powerful data loading/unloading/counting utility for both DSE and Cassandra, similar to COPY. There have been several questions using it or about it.
• ERD notations – refresh your Entity-Relationship conceptual modeling knowledge from RDBMSs, because you may get a few questions on typical ER diagrams.
• hybrid/multi-cloud deployments – a new topic I do not remember from the learning path – you may get some questions about this.

Things I’ve been surprised the exam didn’t cover too much (sometimes not at all):

• generic NoSQL vs RDBMS
• DSE and Cassandra distribution features
• compaction, read repair, snitch, hinted handoff, NodeSync
• read/write path: with SSTables, MemTables, and other internal structures
• no architecture-related internal class names
• tools, config files, more CQL commands

About the Practice Tests

• In your Mercer Mettl dashboard you can try 20 questions they offer for free in an interactive practice exam. The level of detail and difficulty, and the way they are conceived, is the closest to your actual exam questions. All 20 questions are also discussed in detail – with answers and explanations – in this PDF you can download here. Or you can subscribe and wait for a 2-hour workshop they have monthly. Beware the test includes a few questions only for Devs, or only for Admins, from the following courses:
  • DS201 (Foundations) – 10 questions on CQL + 3 questions on Architecture.
  • DS220 (Data Modeling) – 2 questions for Devs only.
  • DS210 (Operations) – 5 questions for Admins only (you don’t need these as Dev).

• From these practice test questions for Devs, or inspired from both the actual exam and the courses from the Developer path, I created two high-quality exam practice tests, with 60 questions each (just like the actual exam) that you can check on Udemy – best price for the next 5 days only with this link to Become a Certified Cassandra Developer: Practice Exams. I’m not aware of any other material (interactive or not) that could help you better to pass the Cassandra Developer exam. Here is an original exam-like question sample:

• Or you can opt-out for the alternative book you can take with you on an iPhone or iPad – look for Apache Cassandra Developer Associate: Exam Practice Tests, in Kindle or paperback edition. It has the exact same practice tests and questions, except it is not interactive. But each practice test is divided into a printed section with all the questions, followed by a section with explained answers and external references for each question. Here is an example of question with a partial answer on an iPad:

Conclusion

• Apache Cassandra is the most popular NoSQL wide-column store, and such a certification can help your Developer career.
• The running special that DataStax offers, to help you pass this proctored certification exam for free, is truly a unique opportunity: use it now, as it may not last forever.
• The exam is challenging, but fair: scenario-based questions are rather fun, and can show if you had real-life use cases to solve.
• Recommended courses do not fully prepare you for the format the exam questions present. The courses are great to teach you about Cassandra (Architecture, Data Modeling and CQL), but the exam itself is a marathon of over 30 problems (out of a total of 60 questions) you must be quick to solve.
• Use my 2 practice tests, each with 60 original exam-like questions, with explanations and references, to increase your success chances at the exam and get a better score!