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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1295) Federated HBase
Date Sat, 25 Apr 2009 03:16:30 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12702647#action_12702647

Andrew Purtell commented on HBASE-1295:

bq. In the case a cluster is down, I guess that would mean the other clusters would have to
keep all the WALs until the it is up again. At that moment, it may receive tons of WALs right?

Yes the effect of a partition and extended outage is a buildup of WALs on the peer clusters,
and then a lot of backlog. Let me think about this case and post a revised slide deck.

bq. Also I was wondering, if you want to add a new cluster, would the way to go be replicating
by hand (MR or else) all the data to the other cluster then telling somehow that the clusters
have a new peer?

I was anticipating that the cluster would be advertised as a peer, somehow, and then replication
would then start. The replicators should add tables and column families to their local schema
on demand as the cells are received, maybe additionally also ask the peer about column family
details as necessary. Whether or not to bring over existing data would be a deployment/application
concern I think and could be handed by a MR export-import job. 

> Federated HBase
> ---------------
>                 Key: HBASE-1295
>                 URL: https://issues.apache.org/jira/browse/HBASE-1295
>             Project: Hadoop HBase
>          Issue Type: New Feature
>            Reporter: Andrew Purtell
>         Attachments: hbase_repl.1.pdf
> HBase should consider supporting a federated deployment where someone might have terascale
(or beyond) clusters in more than one geography and would want the system to handle replication
between the clusters/regions. It would be sweet if HBase had something on the roadmap to sync
between replicas out of the box. 
> Consider if rows, columns, or even cells could be scoped: local, or global.
> Then, consider a background task on each cluster that replicates new globally scoped
edits to peer clusters. The HBase/Bigtable data model has convenient features (timestamps,
multiversioning) such that simple exchange of globally scoped cells would be conflict free
and would "just work". Implementation effort here would be in producing an efficient mechanism
for collecting up edits from all the HRS and transmitting the edits over the network to peers
where they would then be split out to the HRS there. Holding on to the edit trace and tracking
it until the remote commits succeed would also be necessary. So, HLog is probably the right
place to set up the tee. This would be filtered log shipping, basically.  
> This proposal does not consider transactional tables. For transactional tables, enforcement
of global mutation commit ordering would come into the picture if the user  wants the  transaction
to span the federation. This should be an optional feature even with transactional tables
themselves being optional because of how slow it would be.

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