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https://issues.apache.org/jira/browse/HIVE-18238?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16310297#comment-16310297
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Eugene Koifman commented on HIVE-18238:
---------------------------------------

I think AcidUtils.CONF_ACID_KEY (hive.doing.acid) is used to disable 
CombineInputFormat for queries reading Acid tables.
It should be per query rather than per session.
It was most likely introduced back when Driver copied Configuration so the 
"unset" happened automatically.  
If it gets set permanently I don't think that would show up in UTs unless they 
explicitly check for use of CombineInputFormat

> Driver execution may not have configuration changing sideeffects 
> -----------------------------------------------------------------
>
>                 Key: HIVE-18238
>                 URL: https://issues.apache.org/jira/browse/HIVE-18238
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Logical Optimizer
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>         Attachments: HIVE-18238.01wip01.patch, HIVE-18238.02.patch, 
> HIVE-18238.03.patch
>
>
> {{Driver}} executes sql statements which use "hiveconf" settings;
> but the {{Driver}} itself may *not* change the configuration...
> I've found an example; which shows how hazardous this is...
> {code}
> set hive.mapred.mode=strict;
> select "${hiveconf:hive.mapred.mode}";
> create table t (a int);
> analyze table t compute statistics;
> select "${hiveconf:hive.mapred.mode}";
> {code}
> currently; the last select returns {{nonstrict}} because of 
> [this|https://github.com/apache/hive/blob/7ddd915bf82a68c8ab73b0c4ca409f1a6d43d227/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java#L1696]



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