Add expand_nested_docs Parameter support to NMSLIB engine

[heemin32]

Description

Add support for the expand_nested_docs parameter in the nmslib engine. As nmslib does not support multi-vector functionality, this feature may have limited usefulness but poses no downside to including it.

Related Issues

N/A

Check List

• New functionality includes testing.
• [] New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[navneet1v]

As nmslib does not support multi-vector functionality, this feature may have limited usefulness but poses no downside to including it.

Can you explain a bit more on this?

[heemin32]

As nmslib does not support multi-vector functionality, this feature may have limited usefulness but poses no downside to including it.

Can you explain a bit more on this?

For nmslib, searches are performed at the nested document level without deduplicating per parent documents. As a result, multiple inner hits can occur as long as the nested documents belong to the top-K results. In this context, the demand for this functionality may be lower compared to other engines.

For instance, consider an extreme scenario where there are two documents, each containing 10 nested documents. If a query is executed with k=5, it is possible that all five closest vectors come from just one of the two documents. In this case, expanding nested documents would include five additional nested documents with scores lower than the minimum score of the already retrieved nested documents.

[navneet1v]

Please add/update the IT of expand nested docs variable for nmslib engine too.

[heemin32]

Please add/update the IT of expand nested docs variable for nmslib engine too.

Added.

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-2331-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a5fb171b065747a39e7aaae3de330c0fda0800ca
# Push it to GitHub
git push --set-upstream origin backport/backport-2331-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-2331-to-2.x.