Grokbase Groups Hive user August 2010
FAQ

[Hive-user] How HIVE manages a join

Joydeep Sen Sarma
Aug 12, 2010 at 7:19 am
i hate this message: 'THIS PAGE WAS MOVED TO HIVE XDOCS ! DO NOT EDIT!Join Syntax'

why must edits to the wiki be banned if there are xdocs? hadoop has both.

there will always be things that are not captured in xdocs. it's pretty sad to discourage free form edits by people who want to contribute without checking out source. (what is this - the 80s?)
________________________________________
From: Edward Capriolo [edlinuxguru@gmail.com]
Sent: Tuesday, August 10, 2010 2:57 PM
To: hive-user@hadoop.apache.org
Cc: hive-dev@hadoop.apache.org
Subject: Re: How HIVE manages a join

Sorry.
$hive_root/docs/xdocs/language_manual/joins.xml
On Tue, Aug 10, 2010 at 5:57 PM, Edward Capriolo wrote:
This page is is already in version control..

/home/edward/cassandra-handler/docs/xdocs/language_manual/joins.xml

Edward
On Tue, Aug 10, 2010 at 5:15 PM, Carl Steinbach wrote:
Hi Yongqiang,
Please go ahead and update the wiki page. I will copy it over to version
control when you are done.
Thanks.
Carl

On Tue, Aug 10, 2010 at 2:11 PM, yongqiang he <heyongqiangict@gmail.com>
wrote:
In the Hive Join wiki page, it says
"THIS PAGE WAS MOVED TO HIVE XDOCS ! DO NOT EDIT!Join Syntax"

Where should i do the update?

On Fri, Aug 6, 2010 at 11:46 PM, yongqiang he <heyongqiangict@gmail.com>
wrote:
Yeah. The sort merge bucket mapjoin has been finished for sometime,
and seems stable now. I did one skew join but haven't get a chance to
look at another skew join Namit mentioned to me. But definitely should
update the wiki earlier. My bad.

On Fri, Aug 6, 2010 at 8:32 PM, Jeff Hammerbacher <hammer@cloudera.com>
wrote:
Yongqiang mentioned he was going to update the wiki with this
information in
the thread at http://hadoop.markmail.org/thread/hxd4uwwukuo46lgw.

Yongqiang, have you gotten a chance to complete the sort merge bucket
map
join and the other skew join you mention in the above thread?

Thanks,
Jeff

On Fri, Aug 6, 2010 at 3:43 AM, bharath vissapragada
wrote:
Roberto ..

You can find these links useful ..



http://www.slideshare.net/ragho/hive-icde-2010?src=related_normal&rel=2374551
- Simple joins and optimizations..


http://www.slideshare.net/zshao/hive-user-meeting-march-2010-hive-team -
New kind of joins / features of hive ..

Thanks

Bharath.V
4th year Undergraduate..
IIIT Hyderabad

On Fri, Aug 6, 2010 at 12:16 PM, Cappa Roberto
wrote:
Hi,

I cannot find any documentation about what algorithm performs HIVE to
translate JOIN clauses to Map-Reduce tasks.

In particular, if I have two tables A and B, each table is written on
a
separate file and each file is splitted on hadoop nodes. When I
perform a
JOIN with A.column = B.column, the framework has to compare full data
from
the first file and full data from the second file. In order to
perform a
full scan of all possibile combinations of values, how can hadoop
perform
it? If each node contains a portion of each file, it seems not
possible to
have a complete comparison. Does one of the two files enterely
replicated on
each node? Or, does HIVE use another kind of strategy/optimization?

Thanks.
reply

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