max-http-header-size設置

server.max-http-header-size=999999999 //953m

JVM參數配置

-Xms800m -Xmx800m

寫一個rest api

@RestController("action")
public class HttpHandler {
    @PostMapping("/get")
    public String get() {
        return "get";
    }
}

post訪問

 服務端OOM

java.lang.OutOfMemoryError: Java heap space
    at java.nio.HeapByteBuffer.<init>(HeapByteBuffer.java:57) ~[na:1.8.0_152]
    at java.nio.ByteBuffer.allocate(ByteBuffer.java:335) ~[na:1.8.0_152]
    at org.apache.coyote.http11.Http11OutputBuffer.<init>(Http11OutputBuffer.java:107) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
    at org.apache.coyote.http11.Http11Processor.<init>(Http11Processor.java:162) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
    at org.apache.coyote.http11.AbstractHttp11Protocol.createProcessor(AbstractHttp11Protocol.java:990) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:853) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1594) [tomcat-embed-core-9.0.33.jar:9.0.33]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.33.jar:9.0.33]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_152]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_152]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.33.jar:9.0.33]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_152]

debug，分析

而jvm堆的最大大小是800m，第一時間就oom

其實http11InputBuffer也要初始化一個buffer，這個同樣要占很多記憶體。

 為了演示，本文例子比較極端，堆的大小直接小於buffer的大小，一次請求就oom，一般情況下就算堆的大小大於buffer的大小，如果這個max-size設置的不合理過大，隨著請求併發的上升，buffer也會占用大量記憶體，從而導致oom。

max-size設置過小

 異常Request header is too large，導致post的header存不下來，要根據實際情況進行設置這個值。