Features Contributed by SAP

Goetz Lindenmaier edited this page Oct 2, 2018 · 56 revisions

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
8204268: Improve some IncompatibleClassChangeError messages. 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
8204943: Improve message of ArrayStoreException. 11
8205525: Improve exception messages during manifest parsing of jar archives. 12
12

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
8200720: Print additional information in thread dump (times, allocated bytes etc.) 11
8203682: Add jcmd "VM.classloaders" command to print out class loader hierarchy, details 11
8203343: VM.{metaspace|classloaders|classhierarchy...} jcmd should show invocation targets for Generated{Method|Constructor}AccessorImpl classes 11

Java Flight Recorder (JFR)

We will improve Java Flight Recorder and Mission Control as a replacement of SAP JVM Profiler.

since
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.

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

Other

since
8204539: improve error messages in matchJavaTZ [windows] 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
8203014: jcmd should output command list if no command is given 11
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