Mithun Radhakrishnan created HCATALOG-546:
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Summary: 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
Fix For: 0.4.1
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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