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https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12900522#action_12900522
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John Sichi commented on HIVE-1293:
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Did some more testing with latest:
* thrift server is now broken so I'm not able to test multi-conn that way (I
can use CLI + MySQL metastore instead though)
* zookeeper communication is eager, so we start a zk client conn for stuff like
show tables and describe table; can we make it lazy instead?
* EXCLUSIVE/SHARED keyword is still case sensitive
* something I noticed before but forgot to mention: we're getting NPE noise in
the log (below); can we disable the watcher or supply a dummy?
10/08/19 16:12:38 ERROR zookeeper.ClientCnxn: Error while calling watcher
java.lang.NullPointerException
at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:425)
> Concurrency 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.1293.5.patch, hive.1293.6.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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