Friday, October 22, 2010

gemfire pure-java-mode vs native code

http://www.gemstone.com/docs/6.5.0/product/docs/html/Manuals/wwhelp/wwhimpl/js/html/wwhelp.htm#href=SystemAdministratorsGuide/SAG%20Title/TitlePageHTML.html --

GemFire Enterprise can run on platforms not listed in Supported Configurations. This is called running in pure Java mode, meaning GemFire runs without the GemFire native code.

In this mode, the following features may be disabled:
* Operating system statistics. Platform-specific machine and process statistics such as CPU usage and memory size.
* Access to the process ID. Only affects log messages about the application. The process ID is set to "0" (zero) in pure Java mode.

I think most features are available in pure-java-mode (PJM).

I think PJM means gemfire process is not a standalone process but more of a bunch of threads+ConcurrentHashMaps inside a JVM. A standalone process is usually c[1] code running in a dedicated address space. JVM, Perl, bash are all such processes. Such a "c" process makes system calls, which are always (as far as I know) c functions. These system calls aren't available to PJM.

[1]C++ compiles to the same executable code as c. I guess it's assembly code.

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