[Tiered Caching] Bug fix for IndicesRequestCache StaleKey management

[kiranprakash154]

Description

Indices Request Cache Stale Key Management introduced in #12625 had a bug that would have resulted in inaccurate staleKeysCount.

The solution I have come up with is to decrement the staleKeysCount if the readerCacheKeyId has entries in the map, if the map does not have an entry, that means it has been accounted for.

I have modified the logic to skip a notification with Removal Reason of REPLACED, since REPLACED is used when a value of cache is updated but not the key.

All other removal reasons are when a cache entry is deleted and hence is relevant to the staleness calculation.

What was the bug ?

The incrementStaleKeysCount method would remove the entries from the cleanupKeyToCountMap if the count of a readerCacheKeyId would be 0 and/or if the shardId had no entry. This way we would avoid the problem of double counting. This method would also increment the staleKeysCount accordingly.

But on receiving an onRemoval notification on a cache entry being deleted, we would look for the same entry (previously deleted) in the map and deduct the staleKeysCount and hence end up never deducting the staleKeysCount.

Why was this not caught in tests ?

There was a bug in this UT. We closed the reader to create stale keys, but the removal notification we sent was of the secondReader and hence we were able to look up the key for in the cleanupKeyToCountMap and hence deduct the staleKeysCount from 1 to 0.

Manual testing for race condition

For the scenario of a concurrent operation like refresh/close/delete closing a reader right after adding an entry into the cache and before registering the close listener to the reader - we were able to manually verify this with

BytesReference value = cache.computeIfAbsent(key, cacheLoader);
IndexShard indexShard = (IndexShard) cacheEntity.getCacheIdentity();
indexShard.refresh("test");

confirmed this would

• add entry into the map
• enqueue the cleanupKey after the reader actually closes once the search completes.
• removes the entry from the map
• increments the staleKeyCount

Related Issues

Resolves #12540

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

Compatibility status:

Checks if related components are compatible with change 8bfa6c4

Incompatible components

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/flow-framework.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/cross-cluster-replication.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/opensearch-oci-object-storage.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/neural-search.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/performance-analyzer.git]

[github-actions]

❌ Gradle check result for 917df93: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[kiranprakash154]

❌ Gradle check result for 917df93: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

Breaking due to #7396

[github-actions]

❕ Gradle check result for 5a15c87: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.repositories.azure.AzureBlobContainerRetriesTests.testWriteLargeBlob

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[kiranprakash154]

Still see just references to eviction in javadoc instead it should be when any removal of the key happens except Replaced. You will need to merge your paragraphs.

Thanks for catching this, I have updated this

[github-actions]

❕ Gradle check result for 430e57c: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.repositories.azure.AzureBlobContainerRetriesTests.testWriteLargeBlob
      1 org.opensearch.cluster.MinimumClusterManagerNodesIT.testThreeNodesNoClusterManagerBlock

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[github-actions]

✅ Gradle check result for 581ea2a: SUCCESS

[sohami]

lgtm

[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-13070-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 db361ecead1d3c945371c84f4e0ea915c7abcc57
# Push it to GitHub
git push --set-upstream origin backport/backport-13070-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-13070-to-2.x.

[sohami]

@kiranprakash154 backport failed. can you do a manual backport

[kiranprakash154]

@kiranprakash154 backport failed. can you do a manual backport

Yep, on it