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https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12884165#action_12884165
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He Yongqiang commented on HIVE-1293:
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a few questions so far:
1) can the lock implementation guarantee the atomicity? I mean since the lock's
logic happens in client side, it is possible that two concurrent client get
conflicting locks.
2) about realizing locks. if a client did an unlock, will it also release locks
made by other clients? I mean,if a client A did a lock, and then client B did
another lock, and client B did an unlock, will client A still hold its lock?
still reading the code.
> 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
>
>
> 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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