7.16.1 -XX:[+|-]UseCompressedOops

Description

-XX:[+|-]UseCompressedOops specifies whether to enable the functionality for the compressed object pointer. By compressing the size of Java objects for management, the functionality for the compressed object pointer reduces the usage sizes of the JavaHeap area and the Explicit heap area during Java VM execution. Note that this functionality applies to the Explicit heap area only when the explicit memory management functionality is enabled.

To enable this functionality, the following conditions must be met:

• You must be using 64-bit Java VM.

• The sum of the sizes specified for the JavaHeap area and the Explicit heap area must be less than 32 gigabytes.

When Java VM starts up, if the sum of the sizes specified for the JavaHeap area and the Explicit heap area is equal to or greater than 32 gigabytes, Java VM outputs the message below to the standard output and disables the functionality for the compressed object pointer.

Java HotSpot(TM) 64-Bit Server VM warning:  Max heap size too large for 
Compressed Oops

Syntax

-XX:[+|-]UseCompressedOops

Specifiable values

Type: String

-XX:+UseCompressedOops

Java VM compresses the size of Java objects in the JavaHeap area and Explicit heap area for management.

-XX:-UseCompressedOops

Java VM does not compress the size of Java objects in the JavaHeap area and Explicit heap area.

Default value

If the definition item is omitted:

-XX:-UseCompressedOops