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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1642) Convert join queries to map-join based on size of table/row
Date Tue, 16 Nov 2010 21:46:14 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12932666#action_12932666
] 

Namit Jain commented on HIVE-1642:
----------------------------------

hive-default.xml

477 <property>
478	  <name>hive.mapjoin.hashtable.threshold</name>
479	  <value>100000</value>
480	  <description>the threshold for the mapjoin hashtable</description>
481	</property>
482
483	<property>
484	  <name>hive.mapjoin.hashtable.loadfactor</name>
485	  <value>0.75</value>
486	  <description>the load factor for the mapjoin hashtable</description>
487	</property>
488
489	<property>
490	  <name>hive.mapjoin.smalltable.filesize</name>
491	  <value>25000000</value>
492	  <description>The threshold for the input file size of the small tables; if the
file size is smaller than this threshold, it will try to concert the common join into map
join</description>
493	</property>
494
495	<property>
496	  <name>hive.mapjoin.localtask.max.memory.usage</name>
497	  <value>0.90</value>
498	  <description>The max memory usage of the local task for map join</description>
499	</property>
500


Add more comments for the 1,2 and 4 properties.
spelling mistake in the third: concert -> convert


Uncheckout DriverContext.java


Why should backup task be obtained from the resolver ?
It can be created at task creation time itself ?


> Convert join queries to map-join based on size of table/row
> -----------------------------------------------------------
>
>                 Key: HIVE-1642
>                 URL: https://issues.apache.org/jira/browse/HIVE-1642
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Liyin Tang
>             Fix For: 0.7.0
>
>         Attachments: hive_1642_1.patch, hive_1642_2.patch, hive_1642_4.patch
>
>
> Based on the number of rows and size of each table, Hive should automatically be able
to convert a join into map-join.

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