hadoop-hive-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-931) Sorted Group By
Date Wed, 02 Dec 2009 06:50:20 GMT

    [ https://issues.apache.org/jira/browse/HIVE-931?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12784660#action_12784660

Namit Jain commented on HIVE-931:

 } else if (node instanceof exprNodeGenericFuncDesc) { 	
				158 		exprNodeGenericFuncDesc udfNode = ((exprNodeGenericFuncDesc)node); 	
				159 		GenericUDF udf = udfNode.getGenericUDF(); 	
				160 		if(!FunctionRegistry.isDeterministic(udf)) 	
				161 		return; 	
				162 		groupByKeys.addAll(0, udfNode.getChildExprs());

Isnt there a bug here ?

group by foo(foo2(x))

You cant assume that the first child is a column - you should recurse till you get a column

> Sorted Group By
> ---------------
>                 Key: HIVE-931
>                 URL: https://issues.apache.org/jira/browse/HIVE-931
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: He Yongqiang
>             Fix For: 0.5.0
>         Attachments: hive-931-2009-11-18.patch, hive-931-2009-11-19.patch, hive-931-2009-11-20.3.patch,
hive-931-2009-11-21.patch, hive-931-2009-12-01.patch
> If the table is sorted by a given key, we don't use that for group by. That can be very
> For eg: if T is sorted by column c1,
> For select c1, aggr() from T group by c1
> we always use a single map-reduce job. No hash table is needed on the mapper, since the
data is sorted by c1 anyway.
> This will reduce the memory pressure on the mapper and also remove overhead of maintaining
the hash table.

This message is automatically generated by JIRA.
You can reply to this email to add a comment to the issue online.

View raw message