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.

Functional Improvements

Memory Management

Metaspace

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.

	since
8198423: Improve metaspace chunk allocation	11

Java in Containers

Applications run in Containers or the Cloud need to be optimized for small footprint.

	since
8198510: Enable UseDynamicNumberOfGCThreads by default We saw the VM starting too many GC threads.	11
8198756: Lazy allocation of compiler threads We saw the VM starting too many compiler threads.	11
8196062: Enable docker container related tests for linux ppc64le This also needed some functional improvements.	11
8197412: Enable docker container related tests for linux s390x	11

Network

	since
8170868: DefaultProxySelector should use system defaults on Windows, MacOS and Gnome	9

Stack sizes

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.

	since
8170655: [posix] Fix minimum stack size computations	10
8139864: Improve handling of stack protection zones.	10

Exception messages

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.

	since
8197405: Improve messages of AbstractMethodErrors and IncompatibleClassChangeErrors.	10, 11
8199852: Print more information about class loaders in LinkageErrors.	11
8201593: Print array length in ArrayIndexOutOfBoundsException.	11
8203881: Print erroneous size in NegativeArraySizeException	11
8199940: Print more information about class loaders in IllegalAccessErrors	11
	11

Servicability Extensions

Jcmd improvements

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.

	since
8189864: Provide an ascii map to visualize metaspace fragmentation	10
8198691: CodeHeap State Analytics Print information about the memory containing Java methods compiled to native code.	11
8198553: jcmd: separate Metaspace statistics from NMT Introduces new command VM.metaspace.	11
8201572: Improve Metaspace Statistics	11
8203219: VM.metaspace jcmd should optionally show loaded classes for loaders	11
8203455: jcmd: VM.metaspace: print loader name for anonymous CLDs	11
8203682: Add jcmd "VM.classloaders" command to print out class loader hierarchy, details	11
	11

Unified logging

	since
	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.

	since
8191101: Show register content in hs-err file on assert	11
8203292: Print complete set of flags in the hs_err file	11
8202427: Enhance os::print_memory_info on Windows	11
8204476: Add additional statistics to CodeCache::print_summary	11
8204477:Count linkage errors and print in Exceptions::print_exception_counts_on_error	11
	11

Documentation

We improve the documentation, be it Javadoc, the tools etc.

	since
8200384: jcmd help output should be sorted	11
8189102: All tools should support -?, -h and --help	11