HDDS-14699. Fix orphan snapshot versions handling when snapshot chain tableKey mapping is stale

[smengcl]

What changes were proposed in this pull request?

In isSnapshotPurged() check, snapshot chain tableKey returning null should not be the sole indicator for judging whether the snapshot is still active or not.

isSnapshotPurged() incorrectly returning true causes checkOrphanSnapshotVersions() to incorrectly removing active snapshot's YAML metadata (in OmSnapshotLocalDataManagerService runs). This in turn causes NPE in CacheLoader when attempting to load the snapshot.

• Fixed isSnapshotPurged() check
• Added relevant debug logging messages that might be helpful at some point
• Add entries to snapshotIdToTableKey in case of Raft replay in OMSnapshotCreateResponse#addToDBBatch (which was a bug / an oversight previously)
• Check getMeta() nullness first, throw OMEx if null instead of NPE

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-14699

How was this patch tested?

• Added test testCheckOrphanSnapshotVersionsWithStaleSnapshotChain
• Manually tested downstream that with the patch, the issue does not appear in the system test suite again

[Copilot]

Pull request overview

This PR fixes a critical bug where active snapshots were incorrectly marked as purged when the SnapshotChainManager's snapshotIdToTableKey map became stale, leading to NullPointerException in the snapshot cache loader.

Changes:

• Fixed isSnapshotPurged() to fall back to transactionInfo when tableKey lookup returns null, treating snapshots without purge transaction info as active
• Added addSnapshotToTableKey() method to update the snapshotIdToTableKey map during Raft log replay in OMSnapshotCreateResponse#addToDBBatch
• Added debug logging throughout SnapshotChainManager to aid in diagnosing snapshot chain synchronization issues

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
OmSnapshotManager.java	Fixed isSnapshotPurged() logic to handle null tableKey by falling back to transactionInfo check; added debug logging
SnapshotChainManager.java	Added addSnapshotToTableKey() method for Raft replay; enhanced debug logging in getTableKey(), addSnapshot(), and removeFromSnapshotIdToTable()
OMSnapshotCreateResponse.java	Added call to addSnapshotToTableKey() in addToDBBatch() to maintain snapshotIdToTableKey map during Raft replay
TestOmSnapshotLocalDataManager.java	Added regression test testCheckOrphanSnapshotVersionsWithStaleSnapshotChain() to verify fix

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[jojochuang]

apart from the debug log message, the rest is good to go

[jojochuang]

Thanks @smengcl merged.

[smengcl]

Thanks @jojochuang for reviewing and merging this.