Measuring Heap Memory Allocation per HTTP Request in SpringBoot Applications

1. Experiment Idea

In real work, full‑link pressure testing and GC parameter tuning are often needed. Knowing the heap memory required for one RPC or HTTP request allows precise calculation of total heap needed for a given concurrency and estimation of GC frequency.

2. SpringBoot HTTP Interface Declaration

The following code defines a POST endpoint create and a GET endpoint gc for triggering garbage collection.

@Slf4j
@RestController
public class TestController {
    private AtomicLong count = new AtomicLong(0);
    @ResponseBody
    @RequestMapping(value = "create", method = RequestMethod.POST)
    public String create(@RequestBody Order order) {
        //log.warn("收到提单请求 cnt{}:{}", count.getAndIncrement(), order);
        return "ok";
    }
    @ResponseBody
    @RequestMapping(value = "gc", method = RequestMethod.GET)
    public String gc() {
        System.gc();
        return "ok";
    }
}

3. JMeter Test Plan

3.1 Add Thread Group

Configure 10 threads, each looping 2000 times, for a total of 20000 HTTP calls.

3.2 HTTP Defaults

Set the target URL and request body; add a Content-Type: application/json header because the payload is JSON.

4. Experiment Process

4.1 Start SpringBoot Application

Heap size 4 GB, young generation 2 GB, SurvivorRatio=8 (each survivor occupies 1/10 of the young generation). GC log location is set with -Xloggc:/Users/testUser/log/gc.log .

java -server 
-Xmx4g -Xms4g -XX:SurvivorRatio=8 -Xmn2g 
-XX:MetaspaceSize=512m -XX:MaxMetaspaceSize=1g -XX:MaxDirectMemorySize=1g 
-XX:+HeapDumpOnOutOfMemoryError -XX:+PrintGCCause -XX:+PrintGCDetails 
-XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -XX:+PrintTenuringDistribution 
-XX:+UnlockDiagnosticVMOptions -XX:ParGCCardsPerStrideChunk=32768 
-XX:+PrintCommandLineFlags -XX:+UseConcMarkSweepGC -XX:+UseParNewGC 
-XX:ParallelCMSThreads=6 -XX:+CMSClassUnloadingEnabled 
-XX:+UseCMSCompactAtFullCollection -XX:+CMSParallelInitialMarkEnabled 
-XX:+CMSParallelRemarkEnabled -XX:+CMSScavengeBeforeRemark -XX:+PrintHeapAtGC 
-XX:CMSFullGCsBeforeCompaction=1 -XX:CMSInitiatingOccupancyFraction=70 
-XX:+UseCMSInitiatingOccupancyOnly -XX:+PrintReferenceGC 
-XX:+ParallelRefProcEnabled -XX:ReservedCodeCacheSize=256M 
-jar target/activiti-0.0.1-SNAPSHOT.jar

4.2 Manual GC Before Test

Execute curl http://localhost:8080/gc to clean existing objects before the pressure test.

4.3 Run JMeter Test

Execute the JMeter test plan, invoking the HTTP endpoint 20000 times.

4.4 GC Log Analysis

After GC, the Eden space is empty; the memory used before GC equals the total memory allocated by the 20000 HTTP calls, indicating each request’s heap allocation.

5. Experiment Results

Each HTTP request in SpringBoot consumes about 34 KB of heap memory even when the request body contains only 50 characters. Adding a larger detail field (1200 characters) raises the average to about 36 KB, a difference that matches the payload size.

{"userId": 32898493, "productId":39043, "detail": ""}

Enabling request‑level logging increases the average memory consumption to roughly 56 KB per request, showing that log size has a significant impact on memory usage and GC frequency.

6. Real‑world Data

In production, a single RPC request may consume 0.5 MB–1 MB due to complex business logic, multiple downstream calls, database and cache accesses, and extensive logging.

7. Recommendations

Control the size of individual log entries to reduce memory usage and GC frequency, thereby improving overall system performance.