1) Approaching Memory Leaks

Memory leaks in Java often manifest as OutOfMemoryError exceptions or rising heap usage visible in monitoring dashboards. My approach:

1. Reproduce in staging: Apply the same traffic profile (e.g., JMeter load test).
2. Collect a heap dump:

   jmap -dump:format=b,file=heap.hprof <PID>

3. Analyze with tools: Eclipse MAT, VisualVM, or YourKit to detect uncollected references.
4. Fix common causes:
   • Unclosed streams or ResultSets.
   • Static collections holding references.
   • Caches without eviction policies (e.g., replace HashMap with Caffeine).

2) Profiling and Fixing High CPU Usage

High CPU can stem from tight loops, inefficient queries, or excessive logging.

• Step 1: Sample threads

  jstack <PID> > thread-dump.txt

  Identify “hot” threads consuming CPU.

• Step 2: Profile with async profilers like async-profiler or Java Flight Recorder.

  java -XX:StartFlightRecording=duration=60s,filename=recording.jfr -jar app.jar

• Step 3: Refactor:
  • Replace String concatenation in loops with StringBuilder.
  • Optimize regex (use Pattern reuse instead of String.matches()).
  • Review logging level (DEBUG inside loops is expensive).

3) Tuning GC for Low-Latency Services

Garbage collection (GC) can cause pauses. For trading, gaming, or API services, tuning matters:

• Choose the right collector:
  • G1GC for balanced throughput and latency (default in recent JDKs).
  • ZGC or Shenandoah for ultra-low latency workloads (<10ms pauses).
• Sample configs:

  -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -XX:+ParallelRefProcEnabled

• Monitor GC logs with GC Toolkit or Grafana dashboards.

4) Handling Database Bottlenecks

Spring apps often hit bottlenecks in DB queries rather than CPU.

1. Enable SQL logging: in application.properties

   spring.jpa.show-sql=true

2. Profile queries: Use p6spy or database AWR reports.
3. Fixes:
   • Add missing indexes (EXPLAIN ANALYZE is your friend).
   • Batch inserts (saveAll() in Spring Data with hibernate.jdbc.batch_size).
   • Introduce caching (Spring Cache, Redis) for hot reads.
   • Use connection pools like HikariCP with tuned settings:

     spring.datasource.hikari.maximum-pool-size=30