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Features Contributed by SAP
This page lists features of SapMachine that were crafted by SAP to enhance the enterprise-readiness of SapMachine. In general, we contribute these directly upstream to OpenJDK. We might downport these to an earlier version of SapMachine, though. If a feature is not accepted by the OpenJDK community, but considered essential by us, it might only appear in SapMachine. This omits bug fixes, work on our platform ports, work on the build and test infrastructure etc. we do in OpenJDK.
Below tables list the version since which it is available in OpenJDK and SapMachine in bold. If it's only in SapMachine, the version is given in normal letters.
The Metaspace memory region contains metadata for loaded java classes. It can get abnormally large and is a common cause for high memory footprint and Java OOMs, especially when running programs with many class loaders (e.g. JEE), lots of reflection or lambdas.
SAP did significant work in improving the Metaspace allocator. We greatly reduced its memory footprint and made it more predictable. Additionally, we contributed a large number of smaller fixes and improvements.
|8198423: Improve metaspace chunk allocation||11|
Java in Containers
Applications run in Containers or the Cloud need to be optimized for small footprint.
8198510: Enable UseDynamicNumberOfGCThreads by default
We saw the VM starting too many GC threads.
8198756: Lazy allocation of compiler threads
We saw the VM starting too many compiler threads.
8196062: Enable docker container related tests for linux ppc64le
This also needed some functional improvements.
|8197412: Enable docker container related tests for linux s390x||11|
|8170868: DefaultProxySelector should use system defaults on Windows, MacOS and Gnome||9|
Configuring stack sizes used to depend strongly on the system page size and was optimized for 4K pages. We made stack configuration less dependent on the page size wrt. overflow detection and minimal stack sizes.
|8170655: [posix] Fix minimum stack size computations||10|
|8139864: Improve handling of stack protection zones.||10|
Many exceptions thrown in OpenJDK 10 and earlier don't give detailed information about the underlying problem, although it's known when the exception is thrown. We improve these messages step by step.
Jcmd allows to request information from a running Java VM. SAP JVM knows similar tools. We add the commands known in the SAP JVM tools to Jcmd.
Java Flight Recorder (JFR)
We will improve Java Flight Recorder and Mission Control as a replacement of SAP JVM Profiler.
|8207392: [PPC64] Implement JFR profiling.||11|
Retaining information in case of a crash / hs_err file
If OpenJdk crashes, it writes a collection of basic information into a file named hs-err_<process id>.log. This information is very useful to analyze the crash post-mortem. We enrich this printout with information we found useful for SAP JVM support.
|8204539: improve error messages in matchJavaTZ [windows]||11|
We improve the documentation, be it Javadoc, the tools etc.
|8200384: jcmd help output should be sorted||11|
|8189102: All tools should support -?, -h and --help||11|
|8203014: jcmd should output command list if no command is given||11|