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From "stack (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4524) support for more than one region in .META. table
Date Sat, 01 Oct 2011 03:54:45 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13118652#comment-13118652

stack commented on HBASE-4524:

bq. add a feature so that the load balancer can be configured to keep META "alone" with no
other regions on the server. This would be used on big clusters.

When this server crashed, another server would have to be cleared of its regions to dedicate
to meta. There'd be some churn. Log splitting should be fast though.

Changing the balancer would be less intrusive than, for example, having hlog write two logs,
one for user space regions and another for meta edits.

bq. remove ROOT, and just store META directly in ZK (ROOT is essentially vestigial these days)

I'm +1 on killing root.  If we had to have multiple regions in meta table, we could store
all locations in zk and then have client sort them whenever it read the list of metas from

On metadata size, 0.92 shrinks significantly the size per region entry because we remove the
table descriptor per region entry.  We can shrink the meta entry size further if needs be.
 That said, I can imagine we'll start to add data per region (e.g. your region history might
be one such scenario). 

On 1M regions on a cluster, that was the fashion once.  Tendency seems to be toward less bigger
regions per server now though as you say Ming, 10k regionservers makes for a 1M w/ only 100
regions per server.  But 1M rows is not that much though.  You could probably squeeze 1M rows
each with a few versions each into a 256M single region I'd say (Haven't checked).  I'd doubt
this will be the primary obstacle in the way of our getting to 10k cluster size.
> support for more than one region in .META. table
> ------------------------------------------------
>                 Key: HBASE-4524
>                 URL: https://issues.apache.org/jira/browse/HBASE-4524
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Ming Ma
>            Assignee: Ming Ma
> It seems there are some assumptions in the code that .META. table only has one region
FIRST_META_REGIONINFO in the following areas:
> 1) .META. table update with user region info.
> 2) .META. regions assignment.
> 3) .META. table split handling.
> Perhaps we don't have such requirement until we scale to really large number of regions
like 1M.

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