Define Heap Size/ Memory management
HotSpot
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JRockit
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Function
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-Xmx:[size]
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Xmx sets
the maximum size of the heap. Maximum value should be the maximum available,
but in such a way that it does not cause any error, or about 75% of the
system physical memory (depends on the OS).
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-Xms:[size]
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Xms sets the minimum & initial size of the heap.
Recommended to set the same value as the Xmx to minimize allocation
overhead of the heap.
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-Xmn,
-XXNewSize, -XXMaxNewSize
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-Xns
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Xns sets
the size of the Young/ Nursery generation heap. This is the place where new
objects land in the first place before being promoted to the other space.
XX:NewSize - Use this option to set the
New generation Java heap size. Can be set to be one-fourth the size of the
maximum heap size. Increase the value of this option for larger numbers of
short-lived objects.
-XX:MaxNewSize
- Use this option to set the maximum New
generation Java heap size.
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-verbose:gc
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Prints
the additional information
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-XX:+AggressiveHeap
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Configures
the memory system for memory-intensive workloads and sets an expectation to
enable large amounts of memory resources to ensure high throughput. The
JRockit JVM will also use large pages, if available.
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XX:+UseConcMarkSweepGC
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Sets the
garbage collector to use a concurrent strategy
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XX:+UseParallelGC
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Xgc:parallel
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Sets the
garbage collector to use a parallel strategy
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Specifies
what to prioritize: even pause times or maximum throughput
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Specifies
a suitable pause time for the application
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-XX:MaxPermSize
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Define
Maximum heap for the Perm Genaration.
.
(Permanent generation) (non-heap) Stores
classes, methods and other meta data
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Other settings:
- -Xss - If the thread stack size (-Xss) has not been set the default value depends on the threading system and the platform you are running on. When using thin threads the minimum thread stack size is 8 kilobytes and the default is 64 kilobytes. When using native threads the minimum thread stack size is 16 kilobytes. For Windows the default thread stack size when using native threads is 64 kilobytes and for Linux it is 128 kilobytes.
- -XX:SurvivorRatio - The New generation area is divided into several sub-areas: Eden, Survival Space I and Survival Space II. Use the -XX:SurvivorRatio=X option to configure the ratio of the Eden/Survivor Space size. When it is 1:x Eg., -XX:SurvivorRatio=6 - each survivor space will be 1/8 the young generation).
- –XX:NewRatio=n is used divide heap into old and new generation. If we use. -- XX:NewRatio=5, then you create an old-to-new ratio of 5:1; the old generation occupies 5/6 of the heap while the new generation occupies 1/6 of the heap (-XX:NewRatio=3 - the young generation will occupy 1/4 the overall heap).
Tables were taken from the Oracle website, and changed to suit the blog.
