Commvault Software Engineer Interview Guide

The 60-second brief

As a Software Engineer at Commvault, you will design, build, and optimize enterprise-grade software solutions for data management, cloud resilience, backup, and cyber disaster recovery. Commvault is a recognized global leader in enterprise data protection, providing organizations with mission-critical solutions to protect, manage, and recover petabytes of complex data across hybrid, multi-cloud, and on-premises environments. In this role, you sit at the epicenter of system-level performance, low-level engine architectural design, and fault-tolerant storage engineering. Your day-to-day work directly impacts how top global enterprises safeguard their core infrastructure against data loss, ransomware attacks, and system failures.

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

Focus areas

• Data Structures
• Algorithms (Problem Solving)
• System Design

The Commvault interview process

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

Online Assessment

Candidates complete a screening test with technical multiple-choice questions and introductory coding problems.

What to demonstrate

• Candidates complete a screening test with technical multiple-choice questions and introductory coding problems
• Depth in Data Structures

How to prepare

• Answer aloud and timed: Explain the internal implementation of malloc, realloc, and free functions, and describe how you would design a custom memory allocator.
• Answer aloud and timed: What are the structural and execution differences between pure virtual functions, interfaces, and abstract classes in C++ and Java?

Machine Coding Challenge

A multi-hour challenge where candidates build a working solution for a complex problem statement.

What to demonstrate

• A multi-hour challenge where candidates build a working solution for a complex problem statement
• Depth in Data Structures

How to prepare

• Answer aloud and timed: How does pointer arithmetic work in C++, and how do references differ from pointers in memory representation?
• Answer aloud and timed: Explain the mechanics of garbage collection in Java and how you would simulate or manually trigger memory cleanup mechanisms.

Technical Discussion Rounds

2 to 3 rounds focusing on code review, computer science fundamentals, resume project reviews, and system design.

What to demonstrate

• 2 to 3 rounds focusing on code review, computer science fundamentals, resume project reviews, and system design
• Depth in Data Structures

How to prepare

• Answer aloud and timed: What is the performance impact of dynamic casting and virtual function tables (vtables) in object-oriented programs?
• Answer aloud and timed: Given a binary tree, write an efficient algorithm to construct its mirror image or serialize/deserialize its contents.

HR and Managerial Discussion

Final round assessing behavioral alignment and cultural fit within the company.

What to demonstrate

• Final round assessing behavioral alignment and cultural fit within the company
• Depth in Data Structures

How to prepare

• Answer aloud and timed: Implement an algorithm to detect loops in a linked list and remove the cycle without loss of node data.
• Answer aloud and timed: Solve a 0/1 Knapsack variation problem using dynamic programming to minimize total storage cost.

Where candidates lose points

Master File System Abstractions

Prior to your interview, practice building a simplified file system in your chosen language. Ensure you can comfortably manage parent-child node relationships, directory paths, file creation, deletion, and searching.

Review OS Fundamentals Thoroughly

Revisit classic operating system concepts including virtual memory, page replacement algorithms, process synchronization, and file system inodes.

Write Modular, Readable Code

During the machine coding round, prioritize clean architecture, meaningful variable names, proper encapsulation, and robust exception handling over rushed, unstructured code.

Communicate Your Architecture First

Spend the first 30 to 45 minutes of any design or machine coding round planning your class diagrams and data structures. Confirm your design approach with your assigned interviewer or mentor before writing code.

Questions & practice

What are the structural and execution differences between pure virtual functions, interfaces, and abstract cla

Medium · Programming Languages & Object-Oriented

What are the structural and execution differences between pure virtual functions, interfaces, and abstract classes in C++ and Java?

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

How does pointer arithmetic work in C++, and how do references differ from pointers in memory representation?

Medium · Programming Languages & Object-Oriented

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Explain the mechanics of garbage collection in Java and how you would simulate or manually trigger memory clea

Medium · Programming Languages & Object-Oriented

Explain the mechanics of garbage collection in Java and how you would simulate or manually trigger memory cleanup mechanisms.

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

What is the performance impact of dynamic casting and virtual function tables (vtables) in object-oriented pro

Medium · Programming Languages & Object-Oriented

What is the performance impact of dynamic casting and virtual function tables (vtables) in object-oriented programs?

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Given a binary tree, write an efficient algorithm to construct its mirror image or serialize/deserialize its c

Medium · Data Structures & Algorithms

Given a binary tree, write an efficient algorithm to construct its mirror image or serialize/deserialize its contents.

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 an algorithm to detect loops in a linked list and remove the cycle without loss of node data.

Medium · Data Structures & 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?

Solve a 0/1 Knapsack variation problem using dynamic programming to minimize total storage cost.

Medium · Data Structures & 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?

Given two sorted linked lists, merge them in-place with $O(1)$ auxiliary space complexity.

Medium · Data Structures & 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 program to calculate the minimum number of character swaps required to format a string without adjacen

Medium · Data Structures & Algorithms

Write a program to calculate the minimum number of character swaps required to format a string without adjacent identical characters.

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?

Design a data deduplication engine in C++ that scans blocks of incoming files and replaces duplicate chunks wi

Medium · Low-Level System Design & Machine Coding

Design a data deduplication engine in C++ that scans blocks of incoming files and replaces duplicate chunks with reference metadata pointers.

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Explain how virtual memory works, including page tables, translation lookaside buffers (TLBs), and page fault

Medium · Operating Systems & Computer Science Fun

Explain how virtual memory works, including page tables, translation lookaside buffers (TLBs), and page fault handling.

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Describe the core operational differences between processes and threads, including context switching overhead

Medium · Operating Systems & Computer Science Fun

Describe the core operational differences between processes and threads, including context switching overhead and memory sharing.

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Discuss the differences between process synchronization primitives like mutexes, counting semaphores, and spin

Medium · Operating Systems & Computer Science Fun

Discuss the differences between process synchronization primitives like mutexes, counting semaphores, and spinlocks.

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

How do non-clustered and clustered indexes improve query performance in relational databases?

Medium · Computer Networks & Databases

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?

Write a complex SQL query involving multi-table joins, subqueries, and aggregation functions.

Medium · Computer Networks & Databases

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?

Explain the internal implementation of malloc, realloc, and free functions, and describe how you would d

Medium · Programming Languages & Object-Oriented

Explain the internal implementation of malloc, realloc, and free functions, and describe how you would design a custom memory allocator.

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?

Design and implement an in-memory Virtual File System featuring operations like CreateFile, ReadFile, `Rep

Medium · Low-Level System Design & Machine Coding

Design and implement an in-memory Virtual File System featuring operations like CreateFile, ReadFile, ReplaceFileContent, DeleteFile, and MoveFile.

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 implement symbolic and hard links (AddFileLink) inside a custom virtual file system?

Medium · Low-Level System Design & Machine Coding

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?

Implement a backup and restore utility that stores snapshots of files at specific timestamps and restores exac

Medium · Low-Level System Design & Machine Coding

Implement a backup and restore utility that stores snapshots of files at specific timestamps and restores exact file versions on demand.

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?

Build a lightweight driver-rider matching system (similar to a ride-sharing service) using clean object-orient

Medium · Low-Level System Design & Machine Coding

Build a lightweight driver-rider matching system (similar to a ride-sharing service) using clean object-oriented design patterns.

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?

What are buffer overflows, how do they occur at the stack level, and what coding practices prevent them?

Medium · Operating Systems & Computer Science Fun

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 the process of address resolution and how NAT (Network Address Translation) functions across private a

Medium · Computer Networks & Databases

Explain the process of address resolution and how NAT (Network Address Translation) functions across private and public IPs.

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?

What are the functional differences between IPv4 and IPv6, and how do TCP and UDP handle packet transport diff

Medium · Computer Networks & Databases

What are the functional differences between IPv4 and IPv6, and how do TCP and UDP handle packet transport differently?

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 does the operating system handle deadlocks, and what are the primary conditions required for a deadlock to

Medium · Operating Systems & Computer Science Fun

How does the operating system handle deadlocks, and what are the primary conditions required for a deadlock to occur?

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 Commvault candidates report.

Day 1 — Map the Commvault loop

• Write out the reported sequence: Online Assessment, Machine Coding Challenge, Technical Discussion Rounds, HR and Managerial Discussion.
• 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 Data Structures

• Spend the session on Data Structures, which Commvault 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 3 — Work Algorithms (Problem Solving)

• Spend the session on Algorithms (Problem Solving), which Commvault candidates report being tested on.
• Write one worked example in Algorithms (Problem Solving) and time yourself on it.

Deliverable: One timed worked example in Algorithms (Problem Solving).

Day 4 — Work System Design

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

Deliverable: One timed worked example in System Design.

Day 5 — Answer out loud: Programming Languages & Object-Oriented Design

• Answer aloud, timed: Explain the internal implementation of malloc, realloc, and free functions, and describe how you would design a custom memory allocator.
• Answer aloud, timed: What are the structural and execution differences between pure virtual functions, interfaces, and abstract classes in C++ and Java?

Deliverable: Spoken answers to 2 reported Programming Languages & Object-Oriented Design question(s), under time.

Day 6 — Answer out loud: Data Structures & Algorithms

• Answer aloud, timed: Given a binary tree, write an efficient algorithm to construct its mirror image or serialize/deserialize its contents.
• Answer aloud, timed: Implement an algorithm to detect loops in a linked list and remove the cycle without loss of node data.

Deliverable: Spoken answers to 2 reported Data Structures & Algorithms question(s), under time.

Day 7 — Answer out loud: Low-Level System Design & Machine Coding

• Answer aloud, timed: Design and implement an in-memory Virtual File System featuring operations like CreateFile, ReadFile, ReplaceFileContent, DeleteFile, and MoveFile.
• Answer aloud, timed: How would you implement symbolic and hard links (AddFileLink) inside a custom virtual file system?

Deliverable: Spoken answers to 2 reported Low-Level System Design & Machine Coding question(s), under time.

Behavioural preparation

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

Narrate an outage you owned from page to postmortem

Hard · incident response · blast radius · postmortems

Pick an incident you personally drove, ideally one where writes were affected rather than reads. In six to eight minutes: state the symptom as it first appeared on a dashboard, the blast radius you established before you knew the cause, the mitigation you applied and when, the mechanism you eventually proved, and the follow-up that would prevent a repeat. Bring numbers: error rate, tenants affected, minutes to mitigate, minutes to resolve. If you cannot name what you measured, choose a different incident.

Approach

1. Open on the signal rather than the cause: which metric at which percentile moved, on which service, at what time, so the listener follows the same evidence you had rather than a conclusion you already reached.
2. Separate mitigation from diagnosis out loud. State what you did to stop the bleeding (flag off, shed traffic, drain a lease, roll back a deploy) and say plainly that you did it before the mechanism was known, because those are two jobs with different deadlines.
3. Establish blast radius in countable terms: how many tenants, how many writes, and crucially whether the effect was loss or only delay. An append-only revision table or a pending outbox row means the change survived and the projection was merely behind, which is a repair rather than a data-loss incident.
4. Prove the mechanism instead of asserting it. Name the trace span that grew, the plan that flipped to a sequential scan, the lease that expired, plus one alternative you ruled out and the signal that stayed flat while you ruled it out.

Follow-up

• What would you do differently in the first five minutes, given the same dashboard and no more information?
• Which follow-up action did you deliberately not take, and why was dropping it the right call?

Unblock an engineer without taking the keyboard

Easy · mentoring · leases · at-least-once

A teammate has spent two days on a job handler that occasionally writes duplicate rows. They are certain the queue is delivering twice by mistake. You suspect a lease expiring under a slow handler, so the job is running concurrently with itself. Describe how you have unblocked someone in this position: what you asked before offering a hypothesis, what you showed them rather than told them, and what you left them owning. Then say what you would do if their theory turned out to be the right one.

Approach

1. Ask before diagnosing, and ask for things answerable from data they already have: the attempt count on the job rows that produced duplicates, the handler's observed duration against its lease expiry, and whether the duplicate rows share a natural key that a unique constraint could have caught.
2. Teach the shape rather than the answer. A lease cannot distinguish a dead worker from a slow one, so a handler that outruns its lease is running twice by design, and deploys deliver the other half by killing handlers mid-run on every rollout. Both of their candidate theories produce identical duplicate rows, which is why the evidence has to come from timings rather than from argument.
3. Hand over a checklist they execute: a natural key on every write the handler performs so the second copy collides rather than appends, the record of intent written before any external effect, a lease heartbeat while running, and the metric that shows it working.
4. Keep ownership with them deliberately. Pair on the first write, then step back; if you finish it yourself you have closed one ticket and left the same person stuck on the next redelivery.

Follow-up

• How would you distinguish a genuine double-delivery from a lease expiry using only the data already stored?
• Their handler calls an external endpoint before recording that it did. What do you tell them to change first?

Turn a code review disagreement into a decision

Easy · code review · optimistic concurrency · communication

A colleague's change updates a row with UPDATE resource SET version = version + 1 WHERE resource_id = $1 AND version = $2 and treats an affected-row count of zero as a successful no-op. You read that as a silently lost update; they think returning 200 is friendlier to clients than returning a conflict. Describe how you have handled a review disagreement of this shape: what goes in the comment, when you leave the thread, and who decides. Then write the comment you would leave here, in under 80 words.

Approach

1. Sort the disagreement before writing anything. A silently discarded write is a correctness claim about data; the choice between 409 and 412 is taste. Only the first justifies blocking a merge, and saying which one you are doing is most of the value of the comment.
2. Make the claim reproducible in the comment itself with an interleaving rather than a principle: A reads version 7, B reads version 7, B commits version 8, A's predicate matches zero rows, A is told it succeeded and A's edit is gone.
3. Offer the alternative with its cost attached: return 409 carrying the current version and the revision that won, so the client can re-read and re-apply. Note that automatic retry is not the fix, because a retry re-reads the winner's state and reapplies an intent formed against data that no longer exists.
4. Apply an escalation rule you can state: two round trips on the thread, then a call, and the service's owner decides rather than the reviewer. A reviewer who cannot be overruled is a bottleneck with extra steps.

Follow-up

• Where would you put the test that fails if someone reintroduces the swallowed zero rowcount?
• The author says clients cannot handle a 409. How do you check whether that is true?