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Date: Mon, 11 Feb 2013 20:37:14 +0000 (UTC)
From: "Jean-Daniel Cryans (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12478689.1288378930607.274807.1360615034239@arcas>
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Subject: [jira] [Commented] (HBASE-3171) Drop ROOT and instead store META
 location(s) directly in ZooKeeper
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    [ https://issues.apache.org/jira/browse/HBASE-3171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13576096#comment-13576096 ] 

Jean-Daniel Cryans commented on HBASE-3171:
-------------------------------------------

Thanks for looking at the patch guys, much appreciated.

bq. Why not remove the first if block ?

I'm still on the fence about removing some of the core code. We may need to keep it around for migration/upgrade, which I haven't tackled yet.

bq. It would be better if the above method can be removed. It was created to accommodate both -ROOT- and .META. tables.

Comment above + I'd like to verify the semantics of meta tables. It's probably fine to remove, but not there yet.

bq. Should the above method belong to ServerName class ?

I'll look at it, as you can see this new class just has the code from RootRegionTracker.

{quote}
Can remove the constants for ROOT from HConstants.
etc
{quote}

See my first answer to Ted.

bq. The region list template still explains what root is for.

Ah I missed it in my rebase I think, thanks!

                
> Drop ROOT and instead store META location(s) directly in ZooKeeper
> ------------------------------------------------------------------
>
>                 Key: HBASE-3171
>                 URL: https://issues.apache.org/jira/browse/HBASE-3171
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client, master, regionserver, Zookeeper
>            Reporter: Jonathan Gray
>         Attachments: HBASE-3171.patch, HBASE-3171-v2.patch, HBASE-3171-v3.patch, HBASE-3171-v4.patch
>
>
> Rather than storing the ROOT region location in ZooKeeper, going to ROOT, and reading the META location, we should just store the META location directly in ZooKeeper.
> The purpose of the root region from the bigtable paper was to support multiple meta regions.  Currently, we explicitly only support a single meta region, so the translation from our current code of a single root location to a single meta location will be very simple.  Long-term, it seems reasonable that we could store several meta region locations in ZK.  There's been some discussion in HBASE-1755 about actually moving META into ZK, but I think this jira is a good step towards taking some of the complexity out of how we have to deal with catalog tables everywhere.
> As-is, a new client already requires ZK to get the root location, so this would not change those requirements in any way.
> The primary motivation for this is to simplify things like CatalogTracker.  The way we can handle root in that class is really simple but the tracking of meta is difficulty and a bit hacky.  This hack on tracking of the meta location is what caused one of the bugs over in HBASE-3159.

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