HDDS-11137. Removed locks from SnapshotPurge and SnapshotSetProperty APIs.

[hemantk-12]

What changes were proposed in this pull request?

In HDDS-10590, we introduce the locks to achieve synchronization among snapshot purge, set snapshot property, and SSTFilteringService because SSTFilteringService was directly updating the snapshotInfo table and might be causing the snapshot chain corruption.

In HDDS-11068, we found that the snapshot chain corruption issue still exists even after the locks. And the actual reason is that SSTFilteringService directly updates the DB and persists it. More details in HDDS-11068.

In a fix #6965 for HDDS-11068, we removed the logic to persist sstFiltered flag in snapshotInfoTable. Now we create a touch file in snapshot dir which is local to OM node.
Since all the other operations updating snapshotInfoTable go through Ratis, we can rely on OM state machine for the synchronization and remove the unnecessary locking.

What is the link to the Apache JIRA

HDDS-11137

How was this patch tested?

Existing tests.

[swamirishi]

But it wouldn't hurt to have the locking right? Since future changes could still impact this right? Any particular reason why we are removing the locks?

[hemantk-12]

But it wouldn't hurt to have the locking right? Any particular reason why we are removing the locks?

Yes, it is not causing any issues. But these locks are unnecessary right now and are just increasing the complexity.

As mentioned in the description, these locks were added mainly because SSTFilteringService was updating SnapshotInfoTable directly, HDDS-10590. But, in HDDS-11068, we figured that even after adding the locks, it didn't solve the problem and the snapshot chain corruption issue persisted if OM crashed and the double buffer was not flushed.

Since future changes could still impact this right?

As long as any update to SnapshotInfoTable goes through Ratis, we don't need these locks.

[swamirishi]

Thanks for the patch @hemantk-12 The patch looks good to me. Do you think we can add some sort of test case here for this change?

[hemantk-12]

Do you think we can add some sort of test case here for this change?

Can't think of anything on top of my head but I can create a follow up task for it?