What is the purpose of maxdirectmemorysize in the JVM?

maxDirectMemorySize is the maximum capacity of direct memory that the Java Virtual Machine (JVM) can use. Direct memory is a type of memory not limited by the size of the Java heap, and it is allocated by calling native method libraries. By using direct memory, one can interact directly with the operating system when needed, improving memory operation performance.

The purpose of the maxDirectMemorySize parameter is to limit the maximum capacity of direct memory that the JVM can use, preventing the program from accidentally using too much direct memory and causing system crashes or slow performance. When the JVM exceeds the maxDirectMemorySize limit for direct memory usage, an OutOfMemoryError error will be thrown.

It is important to note that the default value of the maxDirectMemorySize parameter is related to the -Xmx parameter (maximum heap memory). By default, the default value of maxDirectMemorySize is half of the maximum heap memory. You can manually set the value of maxDirectMemorySize by using the -XX:MaxDirectMemorySize parameter when starting the JVM.