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