LUCENE-10605: fix error in 32bit jvm object alignment gap calculation

[wormday]

Description

https://issues.apache.org/jira/browse/LUCENE-10605
ArrayUtil.oversize()
The generated array length cannot eliminate the Object alignment gap, wasting some space

[zhaih]

Thanks, overall LGTM, some minor comments on docs

[uschindler]

I think this is a non-risky change. If you did some tests and this behaves better, I am fine!

[zhaih]

Looks great! Thank you for adding the explanation!

[zhaih]

Please add an entry in CHANGES.txt

[wormday]

Please add an entry in CHANGES.txt

Thanks for reminding

[zhaih]

Merged, thank you! Do you want to open a backport PR yourself? @wormday

[wormday]

backport PR

@zhaih Sorry, I don't know how to operate it. Is there a tutorial?

[zhaih]

@wormday Ah basically just apply the same change to branch_9x and open a PR, because the main branch is actually next major version, so if the change is intended to be merged into lucene 9 then we have to open another PR to merge it to branch_9x

The easiest way I guess is to use git cherry-pick to pick the just merged commit.

[wormday]

@zhaih
Thank you very much. I see.
But there seems to be no 32bit since JDK9. Lucene9 does not run under JDK8.
If so, this change only makes sense for Lucene8.
But does the Lucene8 continue to be updated? Do I still need to update branch_9x?

[zhaih]

Hmmm I think we'll only update Lucene8 if there's a bug need to be fixed, so not actively developed.

Let's merge this change into branch_9x anyway, since in the CHANGES.txt we claim it to be in version 9.3, at least it is not harmful

[uschindler]

Hi,
I don't think we need to backport to 8.11 now. We will only do bug fixes anymore and a new release will be seldom. This is not a serious problem, it fixes no bug leading to corrupt indexes or a non working query. It just wastes heap space.

About 32 bit: You can download 32 bit versions of Java also after 9. Oracle does not have them anymore, but other vendors for sure do, e.g. Adoptium: https://adoptium.net/temurin/archive

We don't test them anymore since Lucenes 9, but we could reenable it.

P.S. for backports to 9.x separate pull requests are not needed. For simple changes like this the person who merged the pull request can easily do a simple cherry pick. I do that in most cases automatically. Costs a few seconds and pushing the change to other branch. The additional PR is IMHO too noisy also on mailing lists and really not needed.
Uwe