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https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901553#action_12901553
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John Sichi commented on HIVE-1293:
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With latest patch I am still seeing this in ZK log for each show tables:
2010-08-23 12:31:53,003 - INFO [NIOServerCxn.Factory:2181:nioserverc...@607] -
Connected to /fe80:0:0:0:0:0:0:1%1:59209 lastZxid 0
2010-08-23 12:31:53,003 - INFO [NIOServerCxn.Factory:2181:nioserverc...@639] -
Creating new session 0x12aa06e84940003
2010-08-23 12:31:53,009 - INFO [SyncThread:0:nioserverc...@992] - Finished
init of 0x12aa06e84940003 valid:true
2010-08-23 12:31:53,086 - INFO [ProcessThread:-1:preprequestproces...@384] -
Processed session termination request for id: 0x12aa06e84940003
2010-08-23 12:31:53,088 - INFO [SyncThread:0:nioserverc...@857] - closing
session:0x12aa06e84940003 NIOServerCnxn:
java.nio.channels.SocketChannel[connected local=/fe80:0:0:0:0:0:0:1%1:2181
remote=/fe80:0:0:0:0:0:0:1%1:59209]
> 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.1293.7.patch,
> hive.1293.8.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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