[jira] Resolved: (HIVE-584) Clean up global and ThreadLocal variables in Hive

["Zheng Shao (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Zheng Shao resolved HIVE-584.
-----------------------------

       Resolution: Fixed
    Fix Version/s: 0.5.0
     Release Note: HIVE-584. Clean up global and ThreadLocal variables in Hive. (Yonqqiang He via zshao)
     Hadoop Flags: [Reviewed]

Committed. Thanks Yongqiang!

> Clean up global and ThreadLocal variables in Hive
> -------------------------------------------------
>
>                 Key: HIVE-584
>                 URL: https://issues.apache.org/jira/browse/HIVE-584
>             Project: Hadoop Hive
>          Issue Type: Improvement
>    Affects Versions: 0.3.0, 0.3.1
>            Reporter: Zheng Shao
>             Fix For: 0.5.0
>
>         Attachments: hive-584-2009-9-10.patch, hive-584-2009-9-11.patch
>
>
> Currently in Hive code there are several global and ThreadLocal variables that need to be cleaned.
> Specifically, the following classes are involved:
> 1. HiveConf: contains hive configurations (and a classloader)
> 2. Hive class: contains a static member Hive db. Hive class contains a member HiveConf conf, as well as a ThreadLocal storage of IMetaStoreClient.
> 3. SessionState: contains a static ThreadLocal storage of SessionState. SessionState class contains a Hive db, a HiveConf conf, a history logger, and a bunch of standard input/output streams
> 4. CliSessionState: SessionState plus some command options and the command file name.
> 5. All classes that try to get Hive db or HiveConf from global static Hive db, or SessionState.
> There are several problems with the current design. To name a few:
> 1. SessionState instances are ThreadLocal, but SessionState contains Hive db which also contains ThreadLocal storage. Not sure a db can be shared across different threads or not? What is the global static Hive db?
> 2. We pass HiveConf and Hive db in two ways to classes like Task: Sometimes through initialize(), sometimes through SessionState. This complicates the code a lot. It's hard to know which HiveConf and which db we should use.
> We need to think about a better way to do it.

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