Engineering Manager's Questions

technical questions 1\ how would you approach optimizing a sql query that's running slowly? great response "first, i'd identify the bottlenecks using explain or execution plans to understand query patterns i'd look for full table scans, missing indexes, or inefficient joins for optimization, i'd consider adding appropriate indexes, rewriting joins to reduce data volume early in execution, or restructuring subqueries i'd also evaluate if denormalization might help for read heavy operations after implementing changes, i'd measure improvements with consistent test data and document the performance gains if the query is part of a larger system, i'd also consider caching strategies or materialized views for frequently accessed data patterns " mediocre response "i would run an explain on the query to see what's happening and then add indexes where needed if that doesn't work, i might rewrite some of the joins or break down complex queries into simpler ones i'd test the query afterward to see if it runs faster " poor response "i'd try adding indexes to all columns used in where clauses and joins if that doesn't work, i'd move the query to a more powerful server or add more ram most performance issues can be solved with better hardware " 2\ explain how you would design a data pipeline that processes real time streaming data great response "i'd start by understanding the specific needs data volume, latency requirements, and downstream use cases for architecture, i'd implement a streaming system like kafka or kinesis for ingestion, which provides fault tolerance and scaling capabilities i'd use a stream processing framework like spark streaming, flink, or kafka streams for transformations, with consideration for exactly once processing semantics where needed i'd design the pipeline with monitoring at each stage using metrics like throughput, latency, and error rates for resilience, i'd implement dead letter queues for handling failed messages, retry mechanisms with exponential backoff, and circuit breakers to prevent cascade failures i'd also ensure the system can scale horizontally and handle backpressure effectively " mediocre response "i would use kafka to ingest the streaming data and then process it using spark streaming i'd set up the pipeline to transform and clean the data before loading it into a database i'd add some monitoring to make sure the pipeline is working and set up alerts for when it fails " poor response "i'd use a cloud service like aws kinesis to collect the streaming data and then set up lambda functions to process each record this is the easiest approach since the cloud provider handles most of the complexity if we need to process faster, we can just increase the resources allocated to the service " 3\ how do you ensure data quality in your etl processes? great response "data quality needs to be addressed at multiple levels i build validation into the ingestion layer with schema enforcement and type checking for transformations, i implement data quality rules for format validation, range checking, and business rule compliance i use statistical profiling to detect anomalies and establish baseline metrics i maintain data lineage tracking to help with troubleshooting for monitoring, i set up metrics on completeness, accuracy, consistency, and timeliness with alerts for threshold violations when issues arise, i have automated remediation for common problems and escalation paths for others i document all quality issues in a knowledge base to track recurring patterns and improve prevention mechanisms over time " mediocre response "i typically add validation checks in the etl process to make sure the data meets our requirements i look for nulls, duplicates, and out of range values i also compare record counts between source and destination to make sure we didn't lose any data during the process if there are issues, i set up alerts to notify the team " poor response "we usually have qa teams that check the data quality after the etl process completes for my part, i make sure the etl runs successfully without errors if users report issues with the data, we investigate and fix the etl as needed " 4\ what's your approach to handling slowly changing dimensions in a data warehouse? great response "my approach depends on the business requirements for historical tracking i typically implement scd type 2 for dimensions where historical accuracy is important, maintaining start and end dates and current flags for each version of a record for less critical dimensions, i might use type 1 and simply overwrite old values for complex scenarios, i sometimes implement hybrid approaches like type 6, which combines type 1 and type 2 with effective dating implementation wise, i use merge statements or change data capture to efficiently identify and process changes i also implement surrogate keys rather than relying on natural keys to simplify relationships in the etl, i build specific logic to handle special cases like null values or minor text changes that shouldn't trigger new versions i always document the scd strategy for each dimension to ensure consistency in future development " mediocre response "i usually implement type 1 or type 2 slowly changing dimensions depending on whether we need history for type 2, i add effective date and expiration date columns along with a current flag when data changes, i update the expiration date on the current record and insert a new record with the changes " poor response "i keep it simple by using type 1 scd for most dimensions just overwrite the old data with new data it's much easier to maintain and query if we absolutely need history, i might consider type 2, but it makes the queries more complex and slows down the system " 5\ describe a situation where you had to improve the performance of a large scale data processing job great response "we had a daily batch job processing 500gb of log data that was taking over 12 hours and missing its completion window first, i profiled the job to identify bottlenecks, finding that we were doing repeated full dataset scans and using inefficient join strategies i redesigned the job to partition data by date and region, which allowed for parallel processing i implemented data skipping techniques to avoid processing irrelevant partitions i also identified redundant transformations that were being recalculated instead of reused after refactoring to use broadcast joins for small dimension tables and improving data locality, we reduced processing time to under 3 hours finally, i implemented incremental processing where possible, so we only needed to process new or changed data each run we documented performance patterns and created a monitoring dashboard that tracked job metrics over time to catch regressions early " mediocre response "i had a spark job that was running slowly, so i analyzed the dag visualization to find bottlenecks i noticed we had skewed partitions causing most of the work to happen on just a few executors i repartitioned the data more evenly and adjusted some of the memory settings for the spark executors these changes improved the job performance by about 40% " poor response "i had a slow running job and the easiest solution was to increase the resources allocated to it i doubled the cluster size and the job finished in half the time sometimes throwing more hardware at the problem is the most efficient solution when you have tight deadlines " 6\ how do you approach testing data pipelines? great response "i implement a multi layered testing strategy for data pipelines at the unit level, i test individual transformation functions with controlled inputs and expected outputs for integration testing, i use lightweight test environments with representative data subsets to verify component interactions end to end tests validate the entire pipeline flow with realistic data volumes i specifically focus on edge cases like late arriving data, schema evolution, and error handling for data quality testing, i implement automated validation rules that check for completeness, accuracy, and consistency i use data observability tools to monitor pipeline health in production, tracking metrics like freshness, volume anomalies, and schema drift for critical pipelines, i implement parallel validation where production outputs are compared against previous versions before promoting changes all tests are automated and integrated into our ci/cd workflow to catch issues early " mediocre response "i create test cases for the main pipeline functionality using a test dataset i make sure the transformations work as expected and that the data loads correctly into the target i typically set up some basic automated tests that run when code changes are made, and i do manual testing for complex scenarios " poor response "i test my code by running it on a sample dataset and checking if the output looks right for production changes, i usually implement them and then monitor closely for the first few runs to make sure everything works if there are issues, we can quickly roll back " 7\ explain your experience with data modeling for analytical workloads great response "i've designed both dimensional and data vault models depending on the use case for dimensional modeling, i focus on creating intuitive star schemas with conformed dimensions that enable consistent reporting across fact tables i carefully consider grain decisions based on analysis requirements and design aggregation strategies for performance when using data vault modeling for enterprise data warehouses, i separate business keys, relationships, and descriptive attributes into hubs, links, and satellites, which gives us adaptability to changing source systems for real time analytics, i've implemented hybrid models with streaming aggregates feeding into materialized views i always document the business rules encoded in the model and create data dictionaries for business users my approach balances normalization for data integrity with controlled denormalization for query performance, always keeping the end user analytical needs as the primary design driver " mediocre response "i've worked with star schemas for most of my projects, creating fact and dimension tables based on business requirements i follow standard practices like using surrogate keys and creating date dimensions i try to denormalize where appropriate to improve query performance while keeping the model understandable for business users " poor response "i usually follow whatever the existing data model is in the organization if i need to create one from scratch, i keep it simple by bringing in all the data and organizing it into logical tables that match the source systems the most important thing is getting the data loaded quickly so users can access it " 8\ how do you handle schema evolution in a data pipeline? great response "schema evolution requires careful planning to avoid breaking downstream consumers my approach is to implement a schema registry that tracks all versions of each data structure for development, i follow a backward and forward compatibility strategy when adding fields, i ensure they're nullable so old processors can ignore them when changing field types, i implement dual processing during transition periods for removing fields, i deprecate them first with monitoring to ensure they're no longer being used before actual removal i use technologies like avro or protobuf that support schema evolution gracefully in my etl processes, i implement schema detection and dynamic mapping to handle changes automatically where possible for breaking changes, i use a blue green deployment approach where new schema versions run in parallel until all systems are migrated throughout, i maintain comprehensive documentation of all schema changes with business justifications and migration paths " mediocre response "i design my pipelines to be flexible with new columns by using techniques like dynamically generated sql or schema mapping configurations when schema changes occur, i update the pipeline configurations and test thoroughly before deploying for major changes, i usually coordinate with downstream teams to ensure they're ready for the changes " poor response "when schemas change, i update the etl code to handle the new structure it's usually straightforward to add new fields if fields are removed or types change, we might need to manually fix affected reports or dashboards after deploying the changes " 9\ what strategies do you use for data partitioning and why? great response "i select partitioning strategies based on both query patterns and data characteristics for time series data, i typically partition by time intervals that align with common query ranges daily, weekly, or monthly depending on data volume and retention needs for geographically distributed data, partitioning by region or country can significantly improve locality and enable parallel processing in distributed systems, i also consider partition key selection to avoid skew analyzing cardinality and distribution to ensure balanced workloads for very large tables, i implement multi level partitioning, such as date region combinations i complement partitioning with appropriate clustering or sorting within partitions to optimize range scans when implementing, i carefully weigh the overhead of too many small partitions against query performance and build automated partition management processes for maintenance tasks like archiving old partitions i continually monitor query patterns and partition usage to refine strategies over time " mediocre response "i usually partition data by date since most of our queries filter on date ranges this helps improve query performance by limiting the amount of data scanned for very large tables, sometimes i'll use composite partitioning with date and another high cardinality field i make sure not to create too many partitions to avoid management overhead " poor response "i partition tables when they get too big for efficient queries date partitioning is usually the easiest approach since it's simple to implement the database engine handles most of the optimization, so i don't worry too much about the specific strategy as long as the queries are running " 10\ how do you monitor and troubleshoot data pipelines in production? great response "i implement comprehensive monitoring across several dimensions for operational health, i track pipeline execution metrics like success rates, durations, and resource utilization with historical baselines to detect anomalies for data quality, i monitor volume, completeness, and business rule violations with automated validation checks at critical points i set up detailed logging with consistent correlation ids to trace records through the entire pipeline i also implement data lineage tracking to quickly identify upstream dependencies when issues occur for alerting, i use a tiered approach with different severity levels and appropriate notification channels when troubleshooting, i follow a systematic process identify the failure point through logs and monitoring, isolate the affected data subset, reproduce in a controlled environment when possible, and implement fixes with regression tests i maintain runbooks for common failure scenarios and conduct regular post mortems to improve resilience all of this feeds into dashboards that provide both technical and business relevant views of pipeline health " mediocre response "i set up basic monitoring that tracks if pipelines succeed or fail and how long they take to run i use logging throughout the pipeline code to help with debugging when something fails, i check the logs to see what went wrong and fix the issue for critical pipelines, i set up alerts to notify the team when failures occur " poor response "i rely on the scheduling system to tell me if jobs fail, and then i investigate the specific error messages most data issues are caught by end users when they notice problems in their reports, and then we trace back to find which pipeline had the issue " behavioral/cultural fit questions 11\ tell me about a time when you had to make a difficult decision about technical debt great response "on a data integration project, we were using a homegrown scheduler that was becoming increasingly unreliable as we scaled i identified this as critical technical debt after several production incidents the challenge was that fixing it would delay delivering several business requested features i approached this methodically by quantifying the impact documenting incident frequency, resolution time, and business impact in terms of delayed data i created a proposal with three options ranging from minimal fixes to complete replacement with airflow, including implementation estimates and long term benefits i presented this to both technical leads and business stakeholders, focusing on reliability improvements and long term velocity gains we collectively decided to delay two feature requests and implement airflow, with a phased migration plan to minimize disruption the key was transparency about the tradeoffs and involving stakeholders in the decision this paid off within three months when we saw a 90% reduction in scheduling incidents and improved our ability to implement new integrations faster " mediocre response "we had an etl process using inefficient string parsing that was starting to cause performance issues i knew we needed to refactor it, but we also had upcoming feature deadlines i decided to implement a quick fix for the immediate performance issue while logging a technical debt ticket for a proper refactor later this balanced keeping the system working with our need to deliver new features on time " poor response "we had some poorly written legacy code, but it was working, so i decided not to touch it my priority is always delivering new features on schedule as long as the existing code works adequately, i prefer to focus on new development rather than refactoring old code that might introduce new bugs " 12\ how do you approach collaborating with data scientists and analysts who may have different technical backgrounds? great response "effective collaboration starts with establishing a shared vocabulary and understanding each other's workflows i begin new collaborations by investing time to understand their analytical approaches and how they'll use the data i provide i've found that creating collaborative documentation of data dictionaries and transformation logic is invaluable for data scientists, i focus on providing reliable, well documented datasets with clear lineage and quality metrics they can trust i often set up paired working sessions when developing new data pipelines to ensure we're capturing the right transformations when technical gaps arise, i create abstraction layers like views or simplified interfaces that match their technical comfort level while maintaining underlying best practices i also take opportunities to share knowledge, like running informal sessions on data modeling concepts or learning about their statistical methods the goal is creating a two way partnership where we both contribute our expertise toward solving the business problem " mediocre response "i try to understand what data they need and in what format i make an effort to explain technical constraints in terms they can understand and listen to their requirements sometimes i need to create simplified views or extracts for them if they aren't comfortable with complex sql or our data infrastructure " poor response "i focus on building reliable data pipelines and making sure the data is available they can access what they need through our standard interfaces if they have specific requests, they can submit tickets through our request system, and i'll implement them when i have capacity " 13\ describe a situation where you had to advocate for adopting a new technology or approach great response "our team was struggling with managing increasingly complex data transformation logic in sql scripts i researched dbt (data build tool) as a potential solution for bringing software engineering practices to our transformation layer to advocate for adoption, i first built a small proof of concept using a non critical data mart to demonstrate tangible benefits i documented specific improvements version controlled transformations, automated testing, dependency management, and documentation generation i anticipated concerns about learning curves and migration effort, so i created a phased adoption plan with minimal disruption i set up brown bag sessions to demo the technology and gathered feedback when presenting to leadership, i focused on business outcomes 40% reduction in development time for new transformations, improved quality through automated testing, and enhanced knowledge sharing through generated documentation i secured approval for a pilot project, established success metrics, and after demonstrating value, we gradually expanded adoption the key was combining technical validation with addressing organizational concerns and clearly communicating business value " mediocre response "i suggested we move from using raw sql scripts to using apache airflow for our etl processes i showed my manager some examples of how airflow would make our workflows more manageable and reliable after some discussion about the pros and cons, we decided to try it for a new project, and it worked well enough that we started using it more broadly " poor response "i saw that other companies were using spark for data processing, so i told my team we should adopt it too i pointed out that it's popular and would look good on our resumes some team members were resistant to learning something new, but i insisted it was the future of data processing eventually, management agreed to let us try it " 14\ how do you balance delivering on immediate business needs versus building for long term scalability? great response "this balance requires understanding both business priorities and technical implications i start by classifying requests based on urgency, business impact, and technical complexity for truly urgent business needs, i develop solutions with clear 'technical phases' implementing a minimum viable solution that solves the immediate need while documenting the technical limitations i'm transparent with stakeholders about what trade offs we're making and what future work will be needed for longer term initiatives, i break them into incremental deliverables that provide business value at each stage while progressively building toward the scalable architecture i maintain a technical roadmap alongside the business roadmap, ensuring we allocate roughly 20% of capacity to infrastructure and scalability improvements when conflicts arise, i quantify the costs of technical shortcuts in terms business stakeholders understand future development slowdowns, reliability risks, or scaling limitations this approach has allowed me to maintain technical health while still being responsive to business needs " mediocre response "i try to meet immediate deadlines while building things properly enough that they won't cause problems later when time is tight, i focus on delivering the core functionality but document what needs to be improved later for longer term projects, i try to build more scalable solutions from the start it's always a judgment call based on the specific situation " poor response "business needs always come first i focus on getting solutions delivered on time, even if that means taking some shortcuts we can always go back and improve things later when we have more time in my experience, many of the 'scalability concerns' engineers worry about never actually materialize " 15\ tell me about a time when you had to handle a data security or privacy concern great response "while implementing a customer analytics pipeline, i discovered we were inadvertently collecting and storing personally identifiable information (pii) including email addresses and physical addresses, violating our data governance policies i immediately escalated the issue to my manager and our data protection officer i led a three pronged response first, i implemented an emergency fix that hashed sensitive fields before storage while maintaining referential integrity for analysis second, i conducted a thorough audit of existing data, documenting every instance of pii exposure and created a remediation plan third, i developed a systematic approach to prevent future issues, including automated pii detection in our data validation layer using pattern matching and dictionary lookups i also established a review process for new data sources with a privacy checklist finally, i organized training sessions for the engineering team on privacy best practices and regulatory requirements this experience drove me to become the privacy champion for our team, creating a framework that balanced analytical needs with strict privacy protection " mediocre response "we realized we were storing customer contact information in our analytics database without proper access controls i worked with the security team to identify what fields needed protection and implemented column level encryption for sensitive data we also updated our access policies to restrict who could see the decrypted information after implementing the fix, we did a review to make sure no other sensitive data was exposed " poor response "when the security team notified us about concerns with how we were handling customer data, i quickly restricted access to the database to only essential team members we had tight deadlines, so we continued development while the security team worked on a more comprehensive solution the security team ultimately handled most of the remediation work " 16\ how do you stay current with rapidly evolving data technologies and determine which ones are worth exploring? great response "i maintain a structured approach to technology evaluation that balances exploration with practicality i dedicate 3 4 hours weekly to keeping current through a curated set of sources following key thought leaders, participating in professional communities, and subscribing to research newsletters when evaluating new technologies, i use a framework considering problem fit, ecosystem maturity, operational complexity, and team capabilities for promising technologies, i create learning projects that simulate our actual use cases rather than following tutorials i maintain a personal knowledge base rating technologies i've explored and their suitability for different scenarios to bring this back to the team, i run monthly tech radar sessions where we collectively position technologies as adopt, trial, assess, or hold for technologies in the 'trial' category, we implement controlled proof of concepts with clear evaluation criteria this balanced approach has helped us successfully adopt technologies like dbt and prefect while avoiding others that weren't yet mature enough for our needs " mediocre response "i follow several data engineering blogs and newsletters, and i'm active in a few online communities when i see something interesting, i'll usually try to build a small personal project to get familiar with it for work adoption, i consider factors like community support, documentation quality, and whether it solves a specific problem we have before suggesting we try something new " poor response "i mainly learn about new technologies when they come up in job requirements or when vendors pitch them to our company i focus on mastering the technologies we currently use rather than constantly chasing new trends most new tools end up being repackaged versions of existing concepts anyway " 17\ describe how you've handled a situation where requirements were unclear or constantly changing great response "on a customer behavior analytics project, the marketing team's requirements were initially vague and evolved significantly as they better understood the data's potential rather than waiting for perfect requirements, i implemented an iterative, agile approach with three key components first, i established a foundation of clean, well documented core data entities with clear business definitions that we aligned on second, i built the pipeline with modularity and configurability using parameters for transformation logic and designing for extensibility third, i set up two week development cycles with working demos and feedback sessions when requirements shifted, i would quantify the impact on timeline and technical debt, then collaboratively prioritize with stakeholders throughout the process, i maintained living documentation of decisions and their rationale this approach paid off when the scope expanded to include real time capabilities; because of our modular design, we could adapt without rebuilding the key was treating changing requirements as an expected part of the process rather than an exception, while still maintaining technical integrity " mediocre response "when working on a dashboard project with changing requirements, i tried to build flexibility into the data model from the start i scheduled regular check ins with stakeholders to review progress and gather feedback when requirements changed, i would update our project plan and timelines accordingly i focused on delivering the most stable requirements first while leaving more fluid aspects for later iterations " poor response "i prefer to get clear requirements before starting work when requirements kept changing on a project, i asked the project manager to finalize the specifications so we could stop reworking things i explained that constant changes were inefficient and pushed for a feature freeze so we could complete the original scope before considering new requests " 18\ how do you approach mentoring junior team members or helping others grow their data engineering skills? great response "i believe effective mentoring combines structured guidance with fostering independence i start new mentoring relationships by understanding the individual's background, learning style, and career goals to tailor my approach for technical skill development, i use a progressive method beginning with paired programming sessions where i demonstrate approaches and explain reasoning, then gradually shifting to them driving while i observe and provide feedback i create learning roadmaps with curated resources and small, incremental challenges designed to build confidence beyond technical skills, i focus on developing their problem solving process and system design thinking by walking through my decision making framework on real projects i schedule regular 1 1s with specific discussion points rather than general check ins i've found that having mentees explain concepts back to me or present their work to the team accelerates their growth the most rewarding aspect has been seeing them develop their own styles and approaches rather than just mimicking mine ultimately, i measure success by their increasing autonomy and their ability to mentor others " mediocre response "i try to be available for questions and make time to review junior engineers' code thoroughly i share useful articles or tutorials when i find them for complex tasks, i'll walk through the problem with them and help them break it down into manageable pieces i encourage them to take on increasingly challenging tasks as they become more comfortable " poor response "i give junior team members straightforward tasks they can handle and provide examples they can follow when they have questions, i point them to documentation or show them the solution so they can keep moving forward i find it's most efficient to have clear direction rather than letting them struggle too much " 19\ tell me about a time you had to communicate complex technical details to non technical stakeholders great response "i needed to explain to executive stakeholders why we needed to rebuild our data integration architecture, which was creating data quality issues affecting financial reporting knowing they wouldn't connect with technical details, i prepared a three tiered communication approach first, i created a visual metaphor comparing our data pipeline to a factory production line with clear bottlenecks and quality control issues second, i translated technical metrics into business impact showing specific examples where data delays or inaccuracies led to poor decisions costing measurable amounts third, i presented options with trade offs in business terms short term fixes with continued risks versus a phased rebuild with incremental benefits i avoided technical jargon, focusing instead on reliability, time to insight, and cost implications for the inevitable technical questions, i prepared a 'progressive disclosure' approach starting with high level explanations but having deeper technical details ready if needed the stakeholders appreciated both the clarity and that i respected their time by focusing on business relevance they approved the rebuild with a clear understanding of the value proposition, and stayed engaged throughout the project because they understood its importance " mediocre response "i had to explain to marketing managers why their reports were inconsistent i simplified the technical issues around data integration and prepared some slides showing how data flowed through our systems i focused on explaining the impact of the problem rather than all the technical details they understood enough to approve the time needed to fix the underlying issues " poor response "when explaining technical issues to business users, i keep it as simple as possible they usually don't need or want to understand the details they just want to know when their problem will be fixed i focus on timelines and outcomes rather than trying to explain complex technical concepts that aren't relevant to their role " 20\ how do you handle situations where you disagree with a technical decision made by your team or manager? great response "i approach disagreements as opportunities for deeper understanding and potential innovation first, i make sure i fully understand the rationale behind the decision i ask clarifying questions and listen actively before forming a final opinion if i still have concerns, i prepare by gathering data and examples to illustrate my perspective rather than relying on subjective preferences when discussing the disagreement, i frame it collaboratively 'i have some thoughts on how we might approach this differently' rather than positioning it as a correction i focus on shared goals like system reliability, maintainability, or business outcomes in one specific case, my team decided to build a custom scheduler rather than use an open source solution i disagreed but first sought to understand their concerns about the open source option i then created a small proof of concept addressing those specific concerns and presented a comparison focusing on long term maintenance costs the key was respecting that reasonable people can have different valid perspectives while still advocating for what i believed was the best technical approach once a final decision is made, regardless of outcome, i commit fully to making it successful " mediocre response "i voice my concerns clearly but respectfully, explaining the technical reasons for my different perspective i try to back up my points with examples or data where possible if the team still decides to go in a different direction after hearing my input, i support the decision and help implement it as best i can i believe it's important to have these discussions but also to maintain team cohesion " poor response "i go along with team decisions even if i disagree it's more important to maintain harmony and move forward than to debate every technical decision if problems arise later that i anticipated, i might mention that i had concerns originally, but i try not to make a big deal about it "