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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-77) thread safe query execution
Date Mon, 01 Dec 2008 23:06:44 GMT

    [ https://issues.apache.org/jira/browse/HIVE-77?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12652195#action_12652195
] 

Joydeep Sen Sarma commented on HIVE-77:
---------------------------------------

thx - will fix the inline comments.

static LOG: this is not a blocking issue. I am assuming that log4j itself is multithread safe.
The main issue is that all log events are going to end up in the same log file - and log entries
from different sessions will be interleaved without any clear headers. There's something called
NDC that's apparently used widely in multi-threaded environments to put prefixes on log entries
per thread (in our case session). we can use NDC interfaces from log4j - but it's more work
- potentially more disruptive changes.

QTestUtil: don't understand this. today every query file is run independently in a different
junit test. if QTestUtil ran all of them (either in sequence or in parallel) - this would
not be possible. can u explain a bit more?

> thread safe query execution
> ---------------------------
>
>                 Key: HIVE-77
>                 URL: https://issues.apache.org/jira/browse/HIVE-77
>             Project: Hadoop Hive
>          Issue Type: Bug
>          Components: Server Infrastructure
>            Reporter: Joydeep Sen Sarma
>            Assignee: Joydeep Sen Sarma
>         Attachments: hive-77.patch.1
>
>
> this came up in hive-30 where there's a multithreaded hive server in the works. at the
minimum, the sessionstate objects should be thread local singletons. but filing a more general
bug that can cover this issue + code audit for any other static variables + test suite for
running queries from a multi-threaded environment

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