[
https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12897977#action_12897977
]
John Sichi commented on HIVE-1293:
----------------------------------
Namit, I tried testing with a standalone zookeeper via CLI. Locking a table
succeeded, but then show locks didn't show anything, and unlock said the lock
didn't exist.
I think the reason is that CLI is creating a new Driver for each statement
executed, and when the old Driver is closed, the lock manager is closed along
with it (closing the ZooKeeper client instance). As a result, locks are
released immediately after LOCK TABLE is executed.
When I tested with a thrift server plus two JDBC clients, all was well. I was
able to take a lock from one client and prevent the other client from getting
the same lock. So I guess the thrift server is keeping one Driver around per
connection.
> 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.1293.5.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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
