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Can someone please explain what the JVM option ReservedCodeCacheSize and InitialCodeCacheSize are? Specifically when/why would I want to change it? How do I decide what the right size is?
This is what the docs say:
-XX:ReservedCodeCacheSize=32m Reserved code cache size (in bytes) - maximum code cache size. [Solaris 64-bit, amd64, and -server x86: 2048m; in 1.5.0_06 and earlier, Solaris 64-bit and and64: 1024m.]
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The ReservedCodeCacheSize option determines the maximum size of the codecache. It defaults to a minimum of 32MB for the client JVM and 48MB for the server VM. For most Java applications, this size is so large that the application will never fill the entire codecache.
What Is the Code Cache? Simply put, JVM Code Cache is an area where JVM stores its bytecode compiled into native code. We call each block of the executable native code a nmethod. The nmethod might be a complete or inlined Java method. The just-in-time (JIT) compiler is the biggest consumer of the code cache area.
Abstract. Just-in-time (JIT) compilation coupled with code caching are widely used to improve performance in dynamic programming language implementations. These code caches, along with the associated profiling data for the hot code, however, consume significant amounts of memory.
This code heap contains non-method code such as compiler buffers and bytecode interpreter. This code type stays in the code cache forever. The code heap has a fixed size of 3 MB and remaining code cache is distributed evenly among the profiled and non-profiled code heaps.
ReservedCodeCacheSize (and InitialCodeCacheSize) is an option for the (just-in-time) compiler of the Java Hotspot VM. Basically it sets the maximum size for the compiler's code cache.
The cache can become full, which results in warnings like the following:
Java HotSpot(TM) 64-Bit Server VM warning: CodeCache is full. Compiler has been disabled. Java HotSpot(TM) 64-Bit Server VM warning: Try increasing the code cache size using -XX:ReservedCodeCacheSize= Code Cache [0x000000010958f000, 0x000000010c52f000, 0x000000010c58f000) total_blobs=15406 nmethods=14989 adapters=362 free_code_cache=835Kb largest_free_block=449792 It's much worse when followed by Java HotSpot(TM) Client VM warning: Exception java.lang.OutOfMemoryError occurred dispatching signal SIGINT to handler- the VM may need to be forcibly terminated.
When to set this option?
Normally you'd not change this value. I think the default values are quite good balanced because this problems occur on very rare occasions only (in my experince).
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