[teiid-issues] [JBoss JIRA] (TEIID-2578) add/remove schema elements

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-2578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13310824#comment-13310824 ] 

Steven Hawkins commented on TEIID-2578:
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>  so if non-master node comes up it should be empty to start with.
>  As soon as master node starts it should replicate the events

If the master is up and later a non-master comes up, that is the issue.  The only way this metadata replication works currently is if everyone is up together or if the master joins later.  A non-master joining later won't see the affect of the databasestore load - it will only become aware of vdbs as they are further modified and a reloadDatabase event is issued.

For example in the internal materialization logic there is handling for the state transfer that happens when someone joins the cluster.  Something similar is needed here.

>  but issue could be, what if master node went down in-between and comes back up, it is going to duplicate the state, that needs to be avoided.

Since the master would be issuing a reloadDatabase event, that would replace all of the state on the non-masters.  But it does mean that all existing connections would be terminated.

>  IMO we need to maintain a VDB wide version/lastmodified number that can be passed with all EventDistributor methods. aka. like a if-match-none HEADER in http, What do you think?

There is now only one event distributor method that causes a vdb restart, which is reloadDatabase.  Having a more granular versioning could prevent an unnecessary restart of a vdb from the scenario above but that should be a rare occurrence.

> add/remove schema elements
> --------------------------
>
>                 Key: TEIID-2578
>                 URL: https://issues.jboss.org/browse/TEIID-2578
>             Project: Teiid
>          Issue Type: Feature Request
>          Components: Query Engine
>            Reporter: Ramesh Reddy
>            Assignee: Ramesh Reddy
>             Fix For: 9.2
>
>
> Schemas are currently static after load.  Modifications can only happen with restarts or new versions.  We should allow add/drop at runtime.



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