SapMachine #2250: Add adjustments to heap dumps for the buildpack by schmelter-sap · Pull Request #2251 · SAP/SapMachine

schmelter-sap · 2026-05-19T14:32:45Z

This change adds features to the heap dump for the cf buildpack to be able to store heap dumps for customers in the object store. It includes the following features:

Added -XX:+HeapDumpOverwrite flag. This allows a heap dump to overwrite an existing file. It is also need to write to a named pipe. The latter will be used by the buildpack to stream from the named pipe to the object store. You could already do this in the jcmd GC.heap_dump command.
Added -XX:HeapDumpParallelism=<nr-of-threads> flag. This allows to specify the number of threads to use when writing the heap dump. You could already do this in the jcmd GC.heap_dump command.
When using only one thread to dump the heap, the code will use additional files apart from the heap dump file. This ensures that no extra disk space is used when using only one thread.
Added -XX:+LimitPrimArrayContentInHeapDump flag. If enabled, the heap dump will only write the real content for the first elements of large primitive arrays. The rest is filled with 0 (or false for boolean arrays). This makes the heap dump much more compressible, making upload to the object store faster. The number of entries to keep can be set via -XX:StringLikeContentSizeLimitInHeapDump=<limit> for byte and char arrays (default is 120) or -XX:ArrayContentSizeLimitInHeapDump=<limit> for the other primitive arrays (default is 50).

fixes #2250

SapMachine · 2026-05-20T08:49:29Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

MBaesken · 2026-05-20T11:47:39Z

Couple of minor adjustments might be needed in globals.hpp
"the content of primitive arrays in not completely" should be "is not"
"this only really safes space" should be "saves"
In StringLikeContentSizeLimitInHeapDump description - "primitive char and bytes arrays" should be "byte"

SapMachine · 2026-05-20T13:26:30Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

SapMachine · 2026-05-22T16:45:45Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

SapMachine · 2026-05-28T10:50:12Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

SapMachine · 2026-06-01T09:53:45Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

SapMachine · 2026-06-10T11:59:25Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

dbriemann

One small change needed.

SapMachine · 2026-06-17T09:41:42Z

Hello @schmelter-sap, this pull request fulfills all formal requirements.

dbriemann

lgtm

RealCLanger

Found one minor spelling nit.

And a more general question: Don't you think this could be something to contribute to the OpenJDK? Like "space efficient generation of heap dumps" or such?

RealCLanger · 2026-06-17T14:57:41Z

-  DumpWriter segment_writer(DumpMerger::get_writer_path(writer()->get_file_path(), dumper_id),
-                            writer()->is_overwrite(), writer()->compressor());
+  // SapMachine 2026-05-06: Don't use segments if the dump is not parallel. This makes it
+  // possible to not use any disk space if dumping to a names pipe or a tty.


Suggested change

// possible to not use any disk space if dumping to a names pipe or a tty.

// possible to not use any disk space if dumping to a named pipe or a tty.

schmelter-sap added 7 commits May 7, 2026 11:06

Added heap dump changes for buildpack.

fcccb86

Added test for partial array dump.

bbee3b9

Fixed wrong compression value.

0c82382

Fixed wrong dump order for vthreads.

67e3114

Add missing tests.

81d0ba4

Fixed some descriptions.

f2305a2

Fixed integer overflow

4909815

schmelter-sap requested a review from MBaesken May 20, 2026 08:48

schmelter-sap requested a review from RealCLanger May 20, 2026 08:49

MBaesken reviewed May 20, 2026

View reviewed changes

Comment thread src/hotspot/share/services/heapDumper.cpp

Comment thread src/hotspot/share/runtime/globals.hpp

Comment thread test/hotspot/jtreg/serviceability/HeapDump/PartialArrayContentTest.java

Comment thread test/hotspot/jtreg/serviceability/HeapDump/PartialArrayContentTest.java Outdated

Fixed spellings.

c560113

dbriemann reviewed May 21, 2026

View reviewed changes

MBaesken reviewed May 22, 2026

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Comment thread src/hotspot/share/services/heapDumper.cpp Outdated

Removed SAPJVM comments and change flag name.

1822fef

schmelter-sap added 2 commits May 28, 2026 11:47

Keep trace message even on non-parallel dump.

153d880

Limit the range of parallelism to avoid overflows.

e7a6eea

schmelter-sap added 2 commits June 1, 2026 08:25

Cleanup.

bd235ce

Improved comment.

bd4c739

Make sure the HPROF_HEAP_DUMP_END record is written.

a23703b

schmelter-sap requested review from MBaesken and dbriemann June 16, 2026 08:24

dbriemann reviewed Jun 16, 2026

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Comment thread test/hotspot/jtreg/serviceability/HeapDump/PartialArrayContentTest.java Outdated

Fixes to the test.

f6d6ab6

dbriemann approved these changes Jun 17, 2026

View reviewed changes

RealCLanger reviewed Jun 17, 2026

View reviewed changes

	// possible to not use any disk space if dumping to a names pipe or a tty.
	// possible to not use any disk space if dumping to a named pipe or a tty.

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schmelter-sap commented May 19, 2026 •

edited by RealCLanger

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