hemantk-12 commented on code in PR #4909:
URL: https://github.com/apache/ozone/pull/4909#discussion_r1231401641
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hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/SnapshotChainManager.java:
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@@ -48,6 +47,10 @@
public class SnapshotChainManager {
private static final Logger LOG =
LoggerFactory.getLogger(SnapshotChainManager.class);
+ // Dummy lock to synchronize addSnapshot and deleteSnapshot.
+ // This lock is also used by OMSnapshotCreateRequest to make sure that
+ // snapshot gets added to chain only if addition to cache is successfully.
+ public static final Object LOCK = new Object();
Review Comment:
This lock is also used by `OMSnapshotCreateRequest`.
I tried to explain it
https://github.com/apache/ozone/pull/4909/files#diff-36b9bd9ebbbb4522cfe1ed312e68ea2ac91e9934a92d146ebb52a96644978e49R229-R231
and
https://github.com/apache/ozone/pull/4909/files#diff-36b9bd9ebbbb4522cfe1ed312e68ea2ac91e9934a92d146ebb52a96644978e49R205-R220.
I couldn't think of better idea. Even if I synchronize snapshot creation
separately in `OMSnapshotCreateRequest`, it won't be sufficient. Because
[deleteSnapshot](https://github.com/apache/ozone/blob/master/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/SnapshotChainManager.java#L272)
of `SnapshotChainManager` can be called by `OMSnapshotPurgeResponse`. Which
will leave us in similar situation like
https://github.com/apache/ozone/pull/4909/files#diff-36b9bd9ebbbb4522cfe1ed312e68ea2ac91e9934a92d146ebb52a96644978e49R210-R220
if snapshot gets purge at the same time new gets created.
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