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From "John Sichi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1293) Concurrency Model for Hive
Date Mon, 23 Aug 2010 19:33:22 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901553#action_12901553

John Sichi commented on HIVE-1293:

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:NIOServerCnxn@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:NIOServerCnxn@639] - Creating new
session 0x12aa06e84940003
2010-08-23 12:31:53,009 - INFO  [SyncThread:0:NIOServerCnxn@992] - Finished init of 0x12aa06e84940003
2010-08-23 12:31:53,086 - INFO  [ProcessThread:-1:PrepRequestProcessor@384] - Processed session
termination request for id: 0x12aa06e84940003
2010-08-23 12:31:53,088 - INFO  [SyncThread:0:NIOServerCnxn@857] - closing session:0x12aa06e84940003
NIOServerCnxn: java.nio.channels.SocketChannel[connected local=/fe80:0:0:0:0:0:0:1%1:2181

> 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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