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https://issues.apache.org/jira/browse/HBASE-4495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mikhail Antonov updated HBASE-4495:
-----------------------------------
Status: Open (was: Patch Available)
> CatalogTracker has an identity crisis; needs to be cut-back in scope
> --------------------------------------------------------------------
>
> Key: HBASE-4495
> URL: https://issues.apache.org/jira/browse/HBASE-4495
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 0.94.0
> Reporter: stack
> Assignee: Mikhail Antonov
> Attachments: HBASE-4495-v2.patch, HBASE-4495.patch, HBASE-4495.patch,
> HBASE-4495.patch, HBASE-4495.patch
>
>
> CT needs a good reworking. I'd suggest its scope be cut way down to only
> deal in zk transactions rather than zk and reading meta location in hbase
> (over an HConnection) and being a purveyor of HRegionInterfaces on meta and
> root servers and being an Abortable and a verifier of catalog locations.
> Once this is done, I would suggest it then better belongs over under the zk
> package and that the Meta* classes then move to client package.
> Here's some messy notes I added to head of CT class in hbase-3446 where I
> spent some time trying to make out what it was CT did.
> {code}
> // TODO: This class needs a rethink. The original intent was that it would
> be
> // the one-stop-shop for root and meta locations and that it would get this
> // info from reading and watching zk state. The class was to be used by
> // servers when they needed to know of root and meta movement but also by
> // client-side (inside in HTable) so rather than figure root and meta
> // locations on fault, the client would instead get notifications out of zk.
> //
> // But this original intent is frustrated by the fact that this class has to
> // read an hbase table, the -ROOT- table, to figure out the .META. region
> // location which means we depend on an HConnection. HConnection will do
> // retrying but also, it has its own mechanism for finding root and meta
> // locations (and for 'verifying'; it tries the location and if it fails,
> does
> // new lookup, etc.). So, at least for now, HConnection (or HTable) can't
> // have a CT since CT needs a HConnection (Even then, do want HT to have a
> CT?
> // For HT keep up a session with ZK? Rather, shouldn't we do like
> asynchbase
> // where we'd open a connection to zk, read what we need then let the
> // connection go?). The 'fix' is make it so both root and meta addresses
> // are wholey up in zk -- not in zk (root) -- and in an hbase table (meta).
> //
> // But even then, this class does 'verification' of the location and it does
> // this by making a call over an HConnection (which will do its own root
> // and meta lookups). Isn't this verification 'useless' since when we
> // return, whatever is dependent on the result of this call then needs to
> // use HConnection; what we have verified may change in meantime
> (HConnection
> // uses the CT primitives, the root and meta trackers finding root
> locations).
> //
> // When meta is moved to zk, this class may make more sense. In the
> // meantime, it does not cohere. It should just watch meta and root and
> // NOT do verification -- let that be out in HConnection since its going to
> // be done there ultimately anyways.
> //
> // This class has spread throughout the codebase. It needs to be reigned
> in.
> // This class should be used server-side only, even if we move meta location
> // up into zk. Currently its used over in the client package. Its used in
> // MetaReader and MetaEditor classes usually just to get the Configuration
> // its using (It does this indirectly by asking its HConnection for its
> // Configuration and even then this is just used to get an HConnection out
> on
> // the other end). St.Ack 10/23/2011.
> //
> {code}
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