-Xms / -Xmx
These Oracle® HotSpot™ options set the initial/minimum Java™ heap size, and the maximum heap size respectively. These options are recognized by the Eclipse OpenJ9™ VM.
Notes:
- If you set
-Xms>-Xmx, the VM fails with the message-Xms too large for -Xmx. - If you exceed the limit set by the
-Xmxoption, the VM generates anOutofMemoryError. - If you set a value for
-Xms, the-XX:InitialRAMPercentageoption is ignored. - If you set a value for
-Xmx, the-XX:MaxRAMPercentageoption is ignored.
For the gencon GC policy, you can also use the -Xmo option:
- If the scavenger is enabled,
-Xms≥-Xmn+-Xmo - If the scavenger is disabled,
-Xms≥-Xmo
Syntax
| Setting | Effect | Default |
|---|---|---|
-Xms<size> |
Set initial heap size | 8 MB |
-Xmx<size> |
Set maximum heap size | Half the available memory with a minimum of 16 MB and a maximum of 512 MB |
See Using -X command-line options for more information about the <size> parameter.
See Default settings for the OpenJ9 VM for more about default values.
The -Xmx option can be used with all OpenJ9 GC policies. However, the -Xms option can be used with all GC policies except for the metronome GC policy because the heap is always fully expanded.
Examples
-Xms2m -Xmx64m- Heap starts at 2 MB and grows to a maximum of 64 MB.
-Xms100m -Xmx100m- Heap starts at 100 MB and never grows.
-Xms50m- Heap starts at 50 MB and grows to the default maximum.
-Xmx256m- Heap starts at default initial value and grows to a maximum of 256 MB.