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From "Mithun Radhakrishnan (JIRA)" <>
Subject [jira] [Commented] (HCATALOG-546) Rework HCatalog's JMS Notifications
Date Sat, 12 Jan 2013 02:13:11 GMT


Mithun Radhakrishnan commented on HCATALOG-546:

Alan, please could we also have this patch checked into branch-0.4/? 
> Rework HCatalog's JMS Notifications 
> ------------------------------------
>                 Key: HCATALOG-546
>                 URL:
>             Project: HCatalog
>          Issue Type: Bug
>          Components: notification
>    Affects Versions: 0.4.1
>            Reporter: Mithun Radhakrishnan
>            Assignee: Mithun Radhakrishnan
>             Fix For: 0.6
>         Attachments: HCATALOG-546.branch4.rebased.patch, HCATALOG-546.branch5.patch,
HCATALOG-546.trunk.rebased.patch, sample.Add.Drop.Database.json, sample.Add.Drop.Partition.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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