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