[jira] [Assigned] (HBASE-4495) CatalogTracker has an identity crisis; needs to be cut-back in scope

["Mikhail Antonov (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-4495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mikhail Antonov reassigned HBASE-4495:
--------------------------------------

    Assignee: Mikhail Antonov

> 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
>
> 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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