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Catalist Software Engineer Interview Guide

Catalist Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at Catalist, you are central to building and scaling the technology infrastructure that drives complex data processing, robust web applications, and mission-critical systems. You will collaborate closely with product managers, engineering peers, and cross-functional teams to design, develop, and maintain high-quality software solutions. Your work directly influences the speed, reliability, and capability of the technical products that support key business objectives and data-driven initiatives. This position demands both technical versatility and a collaborative mindset. Whether you are building scalable backend services, optimizing database queries, or contributing to modern frontend architectures, you will be expected to write clean, maintainable, and well-tested code.

This guide is scoped to a Software Engineer candidate at Catalist.

Focus areas

  • Java
  • Algorithms / Coding challenges
  • Data structures

The Catalist interview process

Catalist candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Phone Screen

Initial screening call to assess candidate's background and fit for the role.

What to demonstrate

  • Initial screening call to assess candidate's background and fit for the role
  • Depth in Java

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Interviews

Series of interviews focusing on technical questions and problem-solving scenarios.

What to demonstrate

  • Series of interviews focusing on technical questions and problem-solving scenarios
  • Depth in Java

How to prepare

  • Answer aloud and timed: How do you ensure your code is testable and adheres to established design patterns?
  • Answer aloud and timed: Can you explain how Entity Framework or ORMs manage database relationships and migrations?

Behavioral Assessments

Evaluation of past experiences and collaboration approach through behavioral questions.

What to demonstrate

  • Evaluation of past experiences and collaboration approach through behavioral questions
  • Depth in Java

How to prepare

  • Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
  • Re-read the description of the behavioral assessments above and write down what you would ask to confirm before it.

Final Interview

Possible final interview with senior leadership to assess overall fit and alignment.

What to demonstrate

  • Possible final interview with senior leadership to assess overall fit and alignment
  • Depth in Java

How to prepare

  • Answer aloud and timed: Implement a function to handle data filtering and sorting efficiently.
  • Answer aloud and timed: Write a SQL query involving multiple joins and conditional aggregations to retrieve specific records.

Where candidates lose points

Communicate your thought process

Never code in silence. Talk through your assumptions, why you chose a particular data structure, and how you plan to test your solution.

Be ready for open-ended questions

Some system design or architectural prompts do not have a single correct answer. Focus on discussing trade-offs, scalability limits, and maintainability.

Brush up on fundamentals

Review your computer science basics, including sorting algorithms, time complexity analysis, and common design patterns.

Questions & practice

Explain the role of data structures like hash maps or trees in optimizing search operations.

Medium · Technical and Domain Knowledge

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write a simple algorithm to parse and transform a given dataset within a time constraint.

Medium · Coding and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Implement a function to handle data filtering and sorting efficiently.

Medium · Coding and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write a SQL query involving multiple joins and conditional aggregations to retrieve specific records.

Medium · Database and SQL

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Denormalise tenant onto revisions and backfill it live

Hard · denormalisation · online migration · backfill

resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.

Approach

  1. Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
  2. Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
  3. Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
  4. Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.

Follow-up

  • The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
  • How do you verify the backfill actually finished, given rows are still being inserted while it runs?

How would you design a scalable RESTful API using Java or.NET technologies?

Medium · Technical and Domain Knowledge

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How do you ensure your code is testable and adheres to established design patterns?

Medium · Technical and Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Can you explain how Entity Framework or ORMs manage database relationships and migrations?

Medium · Technical and Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you optimize slow-running database queries or indexing strategies?

Medium · Database and SQL

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain how you handle database transactions and maintain data integrity.

Medium · Database and SQL

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How would you design a popular social networking portal or a similar high-traffic service from scratch?

Medium · System Design and Architecture

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Walk through your approach to solving a theoretical system architecture problem presented by the interviewer.

Medium · System Design and Architecture

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How do you decouple services to improve maintainability and system scalability?

Medium · System Design and Architecture

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How would you approach debugging broken code provided in an IDE environment?

Medium · Coding and Algorithms

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Catalist candidates report.

Day 1 — Map the Catalist loop

  • Write out the reported sequence: Phone Screen, Technical Interviews, Behavioral Assessments, Final Interview.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Java

  • Spend the session on Java, which Catalist candidates report being tested on.
  • Write one worked example in Java and time yourself on it.

Deliverable: One timed worked example in Java.

Day 3 — Work Algorithms / Coding challenges

  • Spend the session on Algorithms / Coding challenges, which Catalist candidates report being tested on.
  • Write one worked example in Algorithms / Coding challenges and time yourself on it.

Deliverable: One timed worked example in Algorithms / Coding challenges.

Day 4 — Work Data structures

  • Spend the session on Data structures, which Catalist candidates report being tested on.
  • Write one worked example in Data structures and time yourself on it.

Deliverable: One timed worked example in Data structures.

Day 5 — Answer out loud: Technical and Domain Knowledge

  • Answer aloud, timed: How would you design a scalable RESTful API using Java or.NET technologies?
  • Answer aloud, timed: Explain the role of data structures like hash maps or trees in optimizing search operations.

Deliverable: Spoken answers to 2 reported Technical and Domain Knowledge question(s), under time.

Day 6 — Answer out loud: Coding and Algorithms

  • Answer aloud, timed: Write a simple algorithm to parse and transform a given dataset within a time constraint.
  • Answer aloud, timed: How would you approach debugging broken code provided in an IDE environment?

Deliverable: Spoken answers to 2 reported Coding and Algorithms question(s), under time.

Day 7 — Answer out loud: Database and SQL

  • Answer aloud, timed: Write a SQL query involving multiple joins and conditional aggregations to retrieve specific records.
  • Answer aloud, timed: How do you optimize slow-running database queries or indexing strategies?

Deliverable: Spoken answers to 2 reported Database and SQL question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Why are you looking for a career change and why are you interested in joining Catalist?

Medium · Behavioral and Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a challenging project from your past work and how you handled obstacles.

Medium · Behavioral and Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle disagreements on technical direction with your peers or management?

Medium · Behavioral and Collaboration

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?