Optimise clone operation for incremental full cluster snapshots

[ashking94]

Description

In this PR, we have improved the logic for snapshot clone operations for full cluster incremental snapshots. The overall logic stays the same. There is no existing coverage for the snapshot clone operation. At this point, it is going to be huge effort to write unit tests for this flow.

Related Issues

Resolves #16295

Check List

• [ ] Functionality includes testing.
• [ ] API changes companion pull request created, if applicable.
• [ ] Public documentation issue/PR created, if applicable.

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[github-actions]

✅ Gradle check result for e273223: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 80.55556% with 7 lines in your changes missing coverage. Please review.

Project coverage is 71.90%. Comparing base (20536ee) to head (0ae74f5).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ava/org/opensearch/snapshots/SnapshotsService.java	80.55%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16296      +/-   ##
============================================
- Coverage     72.00%   71.90%   -0.11%     
+ Complexity    64796    64748      -48     
============================================
  Files          5307     5307              
  Lines        302540   302548       +8     
  Branches      43708    43707       -1     
============================================
- Hits         217853   217548     -305     
- Misses        66801    67124     +323     
+ Partials      17886    17876      -10     

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[github-actions]

✅ Gradle check result for eadc32d: SUCCESS

[dbwiddis]

Generally LGTM. One question.

[dbwiddis]

One more question, does this need a CHANGELOG?

[ashking94]

One more question, does this need a CHANGELOG?

Let me add this, the users may have stopped using clone or have never faced this issue due to lower volume of shards after this inadvertent bug. However, adding a change log may guide the user to explore and try this out.

[github-actions]

✅ Gradle check result for 0ae74f5: SUCCESS

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-16296-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 2166b449d99e5afd9a8d943f7245de2f2635fe5c
# Push it to GitHub
git push --set-upstream origin backport/backport-16296-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-16296-to-2.x.

[ashking94]

Auto backport failed, will create a manual backport.

[ashking94]

Manual backport - #16303