使用JVM内存默认值运行Java Web应用程序

Question

I am running my java web application using my IDE (IntelliJ) and doing a heavy bulk operation, which by now is running since around 5 hours or so. It includes a lot of database inserts, a lot of object creations, I guess it is also kind of CPU intense, and it is not at all heavy on the network.

A current look in my task manager (windows) gives me these numbers:

• CPU: 35%
• RAM: 49%
• IO: 1%
• Network: 0%
• GPU: 5%

Usage by processes, is ...

... orderd by CPU-usage it is like this:

1. "PostreSQL Server"
2. "IntelliJ IDEA (9)"
3. "Google Chrome (16)"

... ordered by memory consumption:

1. "IntelliJ IDEA (9)"
2. "Google Chrome(16)"
3. "OpenJDK Platform binary"

My subjective feeling is definitely, that my computer is hard working, I hear the fan go non-stop and also when switching between windows I witness lag.

I wonder however, why my task manager is not showing that my computer is using one of the resources to its' full extent?

I guess it means, that my application is already using the maximum available memory (limited by the JVM heapsize)? I did not specify this explicitly, and running

java -XX:+PrintFlagsFinal -version | findstr HeapSize

yields these defaults for me:

uintx ErgoHeapSizeLimit                         = 0                                   {product}
    uintx HeapSizePerGCThread                       = 87241520                            {product}
    uintx InitialHeapSize                          := 268435456                           {product}
    uintx LargePageHeapSizeThreshold                = 134217728                           {product}
    uintx MaxHeapSize                              := 4271898624                          {product}
openjdk version "1.8.0_202"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_202-b08)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.202-b08, mixed mode)

I have got 16 GB physical RAM on my machine, do you suggest I should set an explicit value for xms and xmx as described here? How can I increase the JVM memory?

Answer 1

By default, JVM uses 1/4 of available physical memory as MaxHeapSize . If you need more, then you can specify that via -Xmx . It really depends on your application and its needs.

Note that IDEA itself may consume a lot of memory since it's also Java application. If you're worried about performance you should profile your application first (start by something like VisualVM) and then tune as necessary.