JVM Tuning & GC

JVM Tuning, GC Algorithms & Thread Pool Optimization

Deep-dive memory architecture, pause time controls, G1GC vs Generational ZGC, and NIO thread pools.

Performance Engineering

1. Garbage Collection Algorithms Comparison

Collector JVM Flags Target Pause Latency Recommended Heap Range Ideal Workload
G1GC (Default) -XX:+UseG1GC 50ms – 200ms 2 GB – 32 GB+ Standard enterprise web apps, balanced throughput & latency.
Generational ZGC -XX:+UseZGC -XX:+ZGenerational (JDK 21+) < 1ms (Sub-millisecond) 8 GB – 1024 GB Ultra-low latency financial, gaming, real-time trading APIs.
ParallelGC -XX:+UseParallelGC Stop-The-World (Seconds) 512 MB – 8 GB Batch computation, offline ETL processing, memory constrained hosts.

2. Tomcat Connector & Thread Pool Architecture (conf/server.xml)

Tuning the HTTP/1.1 and HTTP/2 NIO connector thread pool prevents thread exhaustion and request starvation:

<Connector port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol"
           connectionTimeout="20000"
           maxThreads="300"
           minSpareThreads="50"
           acceptCount="100"
           maxConnections="8192"
           enableLookups="false"
           compression="on"
           compressionMinSize="2048"
           compressableMimeType="text/html,text/xml,text/plain,text/css,application/json,application/javascript" />
  • maxThreads: Maximum concurrent request processing threads (default 200). Rule of thumb: 1.5 × Peak Concurrent Active Requests.
  • minSpareThreads: Pool of warm standby threads created on boot.
  • acceptCount: Operating system TCP backlog queue when all worker threads are occupied.
  • maxConnections: Maximum open TCP keepalive connections handled asynchronously via epoll/kqueue.