Oracle Interview Questions 2026
Published July 22, 2026 · Updated July 22, 2026
11 real interview questions asked at Oracle. Covers Domain, System Design, Behavioral, SQL / Query Optimization, Java / JVM, SQL / PostgreSQL, Java / Equality. Reported by engineers who went through the Oracle process.
11 questions
289 engineers asked
483 upvotes
Domain (4)
Oracle
Medium
Technical round
PostgreSQLMySQL
Explain Oracle's MVCC (Multi-Version Concurrency Control) and how it enables consistent reads without blocking writers.
How does it differ from SQL Server's locking approach? What are the downsides of MVCC (undo log growth, long-running transactions)?
↑ 88 upvotes · 33 engineers asked this · SDE2
Oracle
Hard
Technical round
PostgreSQLMySQLJava
Explain Oracle's redo log and undo log. How do they work together to provide crash recovery and read consistency? Walk through what happens when a transaction commits, then the server crashes, then restarts.
↑ 51 upvotes · 31 engineers asked this · SDE2
Oracle
Medium
Technical round
PostgreSQLMySQL
Write a SQL query to find the Nth highest salary from an Employee table without using LIMIT/TOP. Then solve it with a window function (DENSE_RANK) and explain which is more portable across Oracle, PostgreSQL, and MySQL.
↑ 63 upvotes · 42 engineers asked this · SDE1
Oracle
Hard
Technical round
JavaDistributed Systems
Explain Oracle RAC (Real Application Clusters). How do multiple nodes access the same database storage? What is the Cache Fusion protocol? When would you choose RAC over a primary-replica setup?
↑ 44 upvotes · 27 engineers asked this · SDE2
System Design (2)
Oracle
Hard
System Design round
Distributed SystemsPostgreSQL
Design a distributed SQL database that supports ACID transactions across shards.
Explain two-phase commit (2PC), its failure modes, and how Google Spanner uses TrueTime to replace 2PC with a more scalable approach.
↑ 41 upvotes · 39 engineers asked this · SDE2
Oracle
Hard
System Design round
Distributed SystemsRedisJava
Design Oracle Cloud's IAM (Identity and Access Management) system. Thousands of customers, each with their own users, groups, and policies. How do you evaluate a permission check in under 10ms for every API call?
↑ 56 upvotes · 34 engineers asked this · SDE2
Behavioral (1)
Oracle
Medium
HR round
Oracle sells to enterprise clients with very long sales cycles. Describe a time you worked closely with a customer (internal or external) to solve a complex technical problem. How did you manage their expectations?
↑ 35 upvotes · 21 engineers asked this · SDE2
SQL / Query Optimization (1)
Oracle
Hard
Technical round
3-7 yearsSQL
A query that joins 4 tables and runs fine on a 1M-row test database takes 40 seconds in production on 500M rows. Walk through your approach to diagnosing and fixing it.
↑ 37 upvotes · 24 engineers asked this · Senior SDE
Java / JVM (1)
Oracle
Medium
Technical round
3-6 yearsJava
Explain the difference between the young generation and old generation in JVM garbage collection. Why do most GC pauses come from minor (young-gen) collections rather than major ones, and when does that assumption break down?
↑ 29 upvotes · 16 engineers asked this · Senior SDE
SQL / PostgreSQL (1)
Oracle
Medium
Technical round
3-6 yearsPostgreSQL
What is the difference between a PostgreSQL VIEW and a MATERIALIZED VIEW? When would a materialized view actually hurt you?
↑ 18 upvotes · 8 engineers asked this · Senior SDE
Java / Equality (1)
Oracle
Medium
Technical round
1-5 yearsJava
Why must you override hashCode() whenever you override equals() in Java? What breaks if you only override equals()?
↑ 21 upvotes · 14 engineers asked this · Senior SDE
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Frequently asked questions
Explain Oracle's MVCC (Multi-Version Concurrency Control) and how it enables consistent reads without blocking writers.
Explain Oracle's MVCC (Multi-Version Concurrency Control) and how it enables consistent reads without blocking writers.
How does it differ from SQL Server's locking approach? What are the downsides of MVCC (undo log growth, long-running transactions)?
Design a distributed SQL database that supports ACID transactions across shards.
Design a distributed SQL database that supports ACID transactions across shards.
Explain two-phase commit (2PC), its failure modes, and how Google Spanner uses TrueTime to replace 2PC with a more scalable approach.
Explain Oracle's redo log and undo log. How do they work together to provide crash recovery and read consistency? Walk through what happens when a transaction commits, then the server crashes, then restarts.
Explain Oracle's redo log and undo log. How do they work together to provide crash recovery and read consistency? Walk through what happens when a transaction commits, then the server crashes, then restarts.
Oracle sells to enterprise clients with very long sales cycles. Describe a time you worked closely with a customer (internal or external) to solve a complex technical problem. How did you manage their expectations?
Oracle sells to enterprise clients with very long sales cycles. Describe a time you worked closely with a customer (internal or external) to solve a complex technical problem. How did you manage their expectations?
Design Oracle Cloud's IAM (Identity and Access Management) system. Thousands of customers, each with their own users, groups, and policies. How do you evaluate a permission check in under 10ms for every API call?
Design Oracle Cloud's IAM (Identity and Access Management) system. Thousands of customers, each with their own users, groups, and policies. How do you evaluate a permission check in under 10ms for every API call?