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https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12857110#action_12857110
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Ashish Thusoo commented on HIVE-1293:
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I would vote for versioning. Since we do not have to deal with the complexity
of a buffer cache I think this would be much simpler to implement than what is
possible in traditional databases. At the same time, for locks we will have to
do a lease based mechanism anyway in order to protect against locks leaking
because of client crashes. And when you account for that, it seems that locking
would not be significantly simpler to implement than versioning.
> 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
>
> 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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