Performance metrics and measurement

Optimizing Code in Java

Pavlos Kosmetatos

Lead Engineer @Wealthyhood

Beyond time measurements

Previous videos
- Measure time taken for operations
- Memory management in the JVM
Moving beyond time measurements
Memory metrics
CPU utilization metrics

Memory metrics with runtime

// Get the Runtime instance
Runtime runtime = Runtime.getRuntime();


// Memory metrics in bytes
long totalMemory = runtime.totalMemory(); // Memory currently allocated
long freeMemory = runtime.freeMemory(); // Memory that is unused
long maxMemory = runtime.maxMemory(); // Maximum memory JVM will attempt to use

All return long numbers representing bytes

Understanding memory metrics

maxMemory(): Maximum memory JVM will attempt to use (set by -Xmx)
totalMemory(): Currently allocated memory to the JVM
freeMemory(): Unused memory
usedMemory(): totalMemory - freeMemory
JVM can increase totalMemory up to maxMemory as needed

Memory metrics in practice

// Create a utility method for readable memory values
public static double getUsedMemoryMB() {
    Runtime runtime = Runtime.getRuntime();
    long memory = runtime.totalMemory() - runtime.freeMemory();
    return memory / (1024.0 * 1024.0);  // Convert to MB
}

// After allocation
System.out.println("Memory used: " + getUsedMemoryMB() + " MB");

Memory used: 5.23 MB

CPU utilization measurement

import java.lang.management.*;

ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();


// Check if CPU time measurement is supported
if (threadMXBean.isThreadCpuTimeSupported()) {
    // Enable CPU time measurement
    threadMXBean.setThreadCpuTimeEnabled(true);

    // Get CPU time in nanoseconds
    long cpuTimeNs = threadMXBean.getThreadCpuTime(Thread.currentThread().threadId());
}

Java profiling tools

JVisualVM: Visual interface for monitoring memory, CPU and more
jmap: Command-line memory analysis tool
These tools go beyond the simple metrics we've discussed!

Let's practice!

Optimizing Code in Java

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