Real-World Scenarios & Interview Challenges

Question 1

What is schema design in database context?

Answer 1

Schema design refers to the structure and organization of a database, including tables, relationships, keys, and constraints.

Question 2

What are soft deletes?

Answer 2

Soft deletes mark records as deleted without actually removing them from the database, typically using a ‘deleted’ flag.

Question 3

What are hard deletes?

Answer 3

Hard deletes permanently remove records from the database, which cannot be recovered without backups.

Question 4

What is a common disadvantage of soft deletes?

Answer 4

Soft deletes can clutter the database with stale data, leading to performance issues if not properly managed.

Question 5

What is a common advantage of hard deletes?

Answer 5

Hard deletes free up storage and simplify queries by removing unnecessary data.

Question 6

What is a best practice for data archiving?

Answer 6

Archive old data in separate tables or databases to keep active data manageable while preserving historical records.

Question 7

What is denormalization in practice?

Answer 7

Denormalization is the process of adding redundancy to a database to improve read performance at the cost of additional storage and potential update anomalies.

Question 8

What’s a real-world use case for denormalization?

Answer 8

In OLAP systems, denormalization helps speed up complex queries and analytics by reducing joins.

Question 9

What is a query optimization walkthrough?

Answer 9

A query optimization walkthrough involves analyzing and refining a SQL query to reduce resource consumption, improve speed, and avoid common pitfalls.

Question 10

What are common steps in query optimization?

Answer 10

Identify slow queries, examine execution plans, adjust indexes, and refactor queries for better efficiency.

Question 11

What is data migration from Oracle to Postgres?

Answer 11

Data migration involves transferring schema, data, and business logic from an Oracle database to a PostgreSQL system, requiring compatibility checks and transformations.

Question 12

What is the challenge of data consistency across services?

Answer 12

Ensuring consistency in distributed systems, especially with eventual consistency models, can be difficult, requiring strategies like eventual consistency, replication, and synchronization.

Question 13

What are best practices for ensuring data consistency?

Answer 13

Use of transactions, distributed locks, idempotent operations, and tools like Kafka or Saga pattern for consistency in microservices.

Question 14

What is the impact of schema design on system performance?

Answer 14

Good schema design ensures fast queries, efficient indexing, and manageable storage, while poor design can lead to slow performance and data integrity issues.

Question 15

What is the architectural implication of data archiving?

Answer 15

Archiving old data allows the active database to stay small and fast, while historical data is available when needed for compliance or analysis.

Question 16

What is the performance tradeoff with soft deletes?

Answer 16

While soft deletes prevent data loss, they can lead to bloated tables and slower queries due to the need to filter out ‘deleted’ records.

Question 17

What’s a fault tolerance tradeoff when migrating from Oracle to Postgres?

Answer 17

Migrating may lead to temporary downtime or data inconsistencies if not properly tested or handled during migration.

Question 18

What is a real-world tradeoff with denormalization?

Answer 18

Denormalization boosts query performance but increases the risk of update anomalies and data inconsistency due to redundant data.

Question 19

What’s a common interview question on schema design?

Answer 19

Can you describe how you would design a schema for a multi-tenant application?

Question 20

What’s a common gotcha with data migration?

Answer 20

Differences in data types, constraints, or SQL syntax between systems (like Oracle and Postgres) can lead to errors if not accounted for.

Question 21

What’s an example of using soft deletes in practice?

Answer 21

E-commerce platforms often use soft deletes for product listings to avoid data loss in case items are mistakenly removed.

Question 22

What is the impact of query optimization on system design?

Answer 22

Optimized queries reduce load on the database, improve application performance, and ensure scalability in high-traffic systems.

Question 23

What’s a common mistake in data consistency across services?

Answer 23

Not handling data synchronization properly, leading to eventual consistency issues where different services have inconsistent views of the data.

Question 24

What is a real-world scenario for SQL in a database system?

Answer 24

Real-world scenarios include data retrieval from large tables, complex reporting, and transactional processing in high-traffic applications like e-commerce platforms.

Question 25

What is an advantage of using SQL for data querying?

Answer 25

SQL provides a standardized and efficient way to query and manipulate relational data, allowing for powerful aggregation and filtering operations.

Question 26

What is a disadvantage of SQL in large-scale systems?

Answer 26

SQL queries can become slow as data grows, and managing joins and complex queries may impact performance in large-scale distributed systems.

Question 27

What is the best practice for indexing in SQL?

Answer 27

Create indexes on columns that are frequently used in search conditions, JOINs, and ORDER BY clauses to improve query performance.

Question 28

What is a common use case for SQL in data-driven applications?

Answer 28

SQL is commonly used in web applications for tasks like user authentication, order processing, and inventory management.

Question 29

How does SQL impact system design?

Answer 29

SQL allows for relational modeling, enforcing data integrity through constraints, which aids in building structured and reliable database systems.

Question 30

Can you provide an example of an SQL join?

Answer 30

A common example is using an INNER JOIN to combine two tables, such as a 'Customers' table and an 'Orders' table, to retrieve customer order history.

Question 31

What is the architectural implication of using SQL databases?

Answer 31

SQL databases follow a structured schema that enforces data consistency, which can help ensure accuracy and reduce errors but might hinder flexibility.

Question 32

What is the performance tradeoff when using SQL databases in large systems?

Answer 32

SQL databases are highly consistent but may face performance bottlenecks as data volume grows, requiring careful indexing and query optimization.

Question 33

What are the fault tolerance considerations when using SQL?

Answer 33

SQL systems can provide fault tolerance through replication, transaction logs, and backups, but high availability configurations may add complexity.

Question 34

How do you monitor SQL queries for performance?

Answer 34

You can use EXPLAIN plans in databases like PostgreSQL and MySQL to analyze query execution paths, identify bottlenecks, and optimize performance.

Question 35

What are real-world tradeoffs with SQL performance?

Answer 35

Optimizing SQL queries often involves tradeoffs between performance and maintainability; heavily optimized queries may be harder to understand and maintain.

Question 36

What is a common interview question about SQL performance?

Answer 36

How would you optimize a slow-running query in a database with millions of records?

Question 37

What’s a potential gotcha with SQL joins in large datasets?

Answer 37

Joins on large datasets can lead to significant performance degradation if proper indexing or query optimization techniques are not applied.

Question 38

What’s a real-world use case for SQL transactions?

Answer 38

SQL transactions are used in scenarios where multiple operations must be completed together, like processing payments or updating inventory in an e-commerce system.

Question 39

How does SQL's ACID compliance impact system design?

Answer 39

ACID compliance ensures that SQL databases maintain data consistency, even in the event of system crashes, which is critical for transactional systems.

Question 40

How do SQL and NoSQL databases differ in system design?

Answer 40

SQL databases enforce strict schema and relationships, which are beneficial for structured data, while NoSQL systems provide flexibility for unstructured or semi-structured data.

Question 41

What is a potential gotcha when designing SQL-based systems for high availability?

Answer 41

Ensuring consistency across replicas in high-availability SQL setups can lead to issues like replication lag or data inconsistency if not carefully managed.