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From "John Sichi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1293) Concurreny Model for Hive
Date Thu, 12 Aug 2010 02:17:20 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12897548#action_12897548
] 

John Sichi commented on HIVE-1293:
----------------------------------

Two configuration questions:

* You have hive.support.concurrency=true in hive-default.xml.  Probably we want it false instead
(only on during tests) since most people using Hive won't have a zookeeper quorum set up?

* Isn't there a default value we can use for hive.zookeeper.client.port?

One lib question:

* Zookeeper is now available from maven.  Maybe we should delete the one in hbase-handler/lib
and get it via ivy instead of adding it in the top-level lib?  The version we have checked
in is 3.2.2, but the maven availability is 3.3.x, so we'd need to test to make sure everything
(including hbase-handler) still works with the newer version.

http://mvnrepository.com/artifact/org.apache.hadoop/zookeeper

Two cleanups:

* In QTestUtil.java, you left the following code commented out; can we get rid of it?

+      //      for (int i = 0; i < qfiles.length; i++) {
+      //        qsetup[i].tearDown();
+      //      }

* In DDLTask.java, you left some commented-out debugging code (two instances):

+        //        console.printError("conflicting lock present " + tbl + " cannot be locked
in mode " + mode);



> Concurreny Model for Hive
> -------------------------
>
>                 Key: HIVE-1293
>                 URL: https://issues.apache.org/jira/browse/HIVE-1293
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Namit Jain
>             Fix For: 0.7.0
>
>         Attachments: hive.1293.1.patch, hive.1293.2.patch, hive.1293.3.patch, hive.1293.4.patch,
hive_leases.txt
>
>
> Concurrency model for Hive:
> Currently, hive does not provide a good concurrency model. The only guanrantee provided
in case of concurrent readers and writers is that
> reader will not see partial data from the old version (before the write) and partial
data from the new version (after the write).
> This has come across as a big problem, specially for background processes performing
maintenance operations.
> The following possible solutions come to mind.
> 1. Locks: Acquire read/write locks - they can be acquired at the beginning of the query
or the write locks can be delayed till move
> task (when the directory is actually moved). Care needs to be taken for deadlocks.
> 2. Versioning: The writer can create a new version if the current version is being read.
Note that, it is not equivalent to snapshots,
> the old version can only be accessed by the current readers, and will be deleted when
all of them have finished.
> Comments.

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