IntermediateTECHNICAL
Suppose your backend service is experiencing intermittent latency spikes under load. Describe, step by step, how you’d investigate the issue at the application level (e.g., thread pools, async vs. sync I/O, database connection pooling, caching) and what metrics, logs, and profiling tools you would use to isolate and resolve the bottleneck.
Backend Developer
General

Sample Answer

When I see latency spikes, I start by confirming them in metrics: p50/p95/p99 latency, error rate, and saturation (CPU, thread pools, DB pool). On one service handling ~2k RPS, we saw p99 jump from 300ms to 3–4s under load. First, I break down latency by endpoint and dependency using tracing (Jaeger) and application metrics. That quickly told us 80% of the spike came from two endpoints blocked on database calls. From there, I check thread pool utilization, queue sizes, and DB connection pool stats; in that incident, the DB pool was maxed and threads were blocking on I/O. We added caching for hot reads (Redis, ~70% hit rate), increased pool size based on actual DB capacity, and moved some work to async tasks. A quick flamegraph profile confirmed most time shifted off blocking JDBC calls. After changes, p99 dropped back under 400ms and we handled ~40% more traffic without regression.

Keywords

Start with metrics: p50/p95/p99, saturation, and error ratesUse tracing to pinpoint which endpoints and dependencies spikeInspect thread pools and DB connection pools for blocking and exhaustionApply targeted fixes: caching, async I/O, tuned pool sizes, and profiling validation
Related Questions

In your civil engineering studies, what specific design coursework or project work did you complete related to irrigation channels or canals (e.g., design of lined/unlined canals, distributaries, minors)? Describe one such design in detail, including how you determined discharge, permissible velocity, section dimensions, and lining choice for Gujarat-type soil and climate conditions.

IntermediateTECHNICAL

Based on your hydrology and irrigation engineering background, explain how you would estimate the irrigation water requirement for a kharif crop in a semi-arid region of Gujarat. Walk me through each step: from reference evapotranspiration estimation, crop coefficient selection, effective rainfall calculation, to arriving at canal discharge for a given command area.

IntermediateTECHNICAL

Walk me through a recent multi-channel digital marketing campaign you managed end-to-end. How did you set objectives, choose channels, allocate budget, and measure success?

IntermediateBEHAVIORAL

In your resume you note improving or optimizing [a process, KPI, or metric]. What specific baseline metrics did you start from, what steps did you personally take, and how did you verify that the improvement was due to your changes rather than external factors?

IntermediatePROBLEM_SOLVING

On your resume you mention working on a cross-functional project (e.g., involving multiple teams or stakeholders). Describe a situation from that project where priorities conflicted—how did you navigate the trade-offs and what was the final outcome?

IntermediateSITUATIONAL