What is Memory tuning: -XX:MaxDirectMemorySize?

Usage:                                                    

To limit amount of memory that can be reserved for all direct byte buffers use:

-XX: MaxDirectMemorySize=size[unit], where size represents the amount of memory you want to limit to, with unit possible values [k|K|m|M|g|G]

Examples:

Limits memory size to 20 Megabytes:

-XX:MaxDirectMemorySize=
20M

Description:

Sets the maximum total size (in bytes) of the java.nio package, direct-buffer allocations. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, and g or G to indicate gigabytes. By default, the size is set to 0, meaning that the JVM chooses the size for NIO direct-buffer allocations automatically.

Default Value:

By default, it is set to 0. Since JDK11 amount of heap memory used for Direct Byte Buffers limited to the same value as the maximum heap size.

Errors:

None

Arguments related:

TODO link UseG1GC, MinHeapFreeRatio, MaxHeapFreeRatio, Xmx, Xms

Related Posts:

• Garbage collection tuning
• Garbage collectors documentation
• Direct memory size

NOTE:

If you have additional comments, interesting experiences or even point of disagreement with this JVM argument description, please leave a comment. Your insights will help the entire 10+ million java developer community to develop one standard source of documentation for all the JVM arguments.