On Thu, 17 Sep 2026 08:41:04 GMT, Oli Gillespie <[email protected]> wrote:
>> Heap dumps offer the ability to exclude unreachable objects, but they >> actually still include GC filler objects/arrays (see >> https://tschatzl.github.io/2022/09/26/jdk-vm-internal-fillerarray.html for >> more on fillers). >> >> If the user requests to exclude unreachable objects/include only live >> objects, heap dump triggers a full GC before dumping, so in theory only live >> objects remain. But filler objects can 'survive' a full GC even though they >> are unreachable by definition. They waste space, and cause confusion. If >> using a tool like MAT, they will show as unreachable - why are unreachable >> objects in my live heap dump? If using something like JOL to show a >> histogram, reachability is not assessed and the user may not notice that >> unreachable objects are influencing the results. They show as `int[]`, so >> their provenance is not obvious. >> >> So, exclude them explicitly if the user requested only live objects. This >> does not affect non-live dumps (discussion for that in >> [JDK-8372389](https://bugs.openjdk.org/browse/JDK-8372389)). >> >> >> $ ls -lah >> 1.5G Sep 14 13:30 live-after-fix.hprof >> 2.6G Sep 14 13:30 live-before-fix.hprof >> >> $ java -jar jol-cli.jar heapdump-stats live-before-fix.hprof >> >> INSTANCES SIZE SUM SIZE CLASS >> ------------------------------------------------------------------------------------------------ >> 5 236,870,896 1,184,354,480 int[59217720] <--- >> filler arrays! >> >> >> --------- >> - [x] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). > > Oli Gillespie has updated the pull request incrementally with two additional > commits since the last revision: > > - Revert "Rename skip_filler_objects -> should_skip_filler" > > This reverts commit ad572794d548c2d6154d80640d01f14b1941a4e8. > - Rename skip_filler_objects -> should_skip_filler Thanks for reviews ------------- PR Comment: https://git.openjdk.org/jdk/pull/32860#issuecomment-5717246795
