[BUG] Block using memory optimized search for indices created before 2.17

[0ctopus13prime]

What is the bug?
When an index was created before 2.17, and user upgrades the cluster to 3.1 and turn on memory optimized search, then NPE will be raised from SegmentReader.getVectorReader as old codec does not have the implementation. We added getVectorReader to return non-null NativeEngines990KnnVectorsReader at version 3.1.

We should fix this check to check the index created version and return false accordingly.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Spin up 2.17 cluster
2. Configure Faiss knn field.
3. Upgrade the cluster to 3.1
4. Turn on memory optimized search.

What is the expected behavior?
A clear and concise description of what you expected to happen.

What is your host/environment?

• OS: Linux
• Version : 3.1
• Plugins : kNN

Do you have any screenshots?
If applicable, add screenshots to help explain your problem.

Do you have any additional context?
Add any other context about the problem.

[0ctopus13prime]

Also we need to ensure the check is blocking NMSLIB as well.
cc @navneet1v

[0ctopus13prime]

Official doc update : opensearch-project/documentation-website#11173

[navneet1v]

@0ctopus13prime the check only applies for index < 2.17. I updated the title of the issue. Let me know if this incorrect.

[0ctopus13prime]

Hi @navneet1v
Thank you!
I remember, in BWC testing, those indices created before 2.19 were failing (including 2.17, 2.18). That's why I added the logic to allow only indices created >= 2.19.
But, let me rerun it to double check it.

[navneet1v]

We should see why they are failing because if memory optimized search needs KNNVectorsFormat then its there from 2.17 . So ideally it should not fail