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https://issues.apache.org/jira/browse/HCATALOG-546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537452#comment-13537452
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Mithun Radhakrishnan commented on HCATALOG-546:
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Looks like the branch4 patch is fine. (No rebase required. It doesn't have the
unused imports. MessagingUtils private constructor has been added, etc.)
If this looks acceptable, let's check this in after HCATALOG-556.
> Rework HCatalog's JMS Notifications
> ------------------------------------
>
> Key: HCATALOG-546
> URL: https://issues.apache.org/jira/browse/HCATALOG-546
> Project: HCatalog
> Issue Type: Bug
> Components: notification
> Affects Versions: 0.4.1
> Reporter: Mithun Radhakrishnan
> Assignee: Mithun Radhakrishnan
> Fix For: 0.4.1
>
> Attachments: HCATALOG-546.branch4.patch,
> HCATALOG-546.trunk.rebased.patch, sample.Add.Drop.Database.json,
> sample.Add.Drop.Partition.json, sample.Add.Drop.Table.json
>
>
> In 0.4.1, the NotificationListener listens for metastore operations and emits
> JMS notifications containing the entire metastore-objects
> (Database/Table/Partitions) in Java-serialized form. The assumption at the
> time was that consumers might need access to the whole object. This policy
> poses a couple of problems:
> 1. The notifications are verbose, since it conveys a bunch of information
> that's available from querying the metastore anyway.
> 2. Consumers of these JMS notifications (e.g. Oozie) would now be dependent
> on the Java class definitions of metastore-objects. If they change, Oozie
> would also need to be restarted (with updated libs), to consume the
> notifications.
> Ideally, the notifications should convey only the minimum information that
> identifies the metastore-change unambiguously. (Everything else can be
> queried for.) They should be backward compatible. If new fields are added,
> existing consumers shouldn't break (unless they intend to consume the new
> fields). Also, the notification-format ought to be pluggable.
> For the initial rework, we're proposing to use a JSON-string to represent the
> notification-content. We're also proposing a helper-class for the likes of
> Oozie to use, that converts the strings to POJOs, in a backward-compatible
> fashion.
> I'll attach sample notifications and a tentative patch shortly.
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