Hadoop's Map-side join implements Hash join?

Posted by ge0rgi0 on Stack Overflow See other posts from Stack Overflow or by ge0rgi0
Published on 2010-05-12T22:47:18Z Indexed on 2010/06/03 3:24 UTC
Read the original article Hit count: 321

Filed under:

join

|

hash

|

hadoop

I try to implement Hash join in Hadoop.

However, Hadoop seems to have already a map-side join and a reduce - side join already implemented.

What is the difference between these techniques and hash join?

© Stack Overflow or respective owner

Related posts about join

Improving Partitioned Table Join Performance

as seen on SQL Blog - Search for 'SQL Blog'
The query optimizer does not always choose an optimal strategy when joining partitioned tables. This post looks at an example, showing how a manual rewrite of the query can almost double performance, while reducing the memory grant to almost nothing. Test Data The two tables in this example use… >>> More
MS SQL 2008, join or no join?

as seen on Stack Overflow - Search for 'Stack Overflow'
Just a small question regarding joins. I have a table with around 30 fields and i was thinking about making a second table to store 10 of those fields. Then i would just join them in with the main data. The 10 fields that i was planning to store in a second table does not get queried directly, it's… >>> More
SQL Server 2008, join or no join?

as seen on Stack Overflow - Search for 'Stack Overflow'
Just a small question regarding joins. I have a table with around 30 fields and i was thinking about making a second table to store 10 of those fields. Then i would just join them in with the main data. The 10 fields that i was planning to store in a second table does not get queried directly, it's… >>> More
Simple join gives unnecessary rows,How to get join properly with only matches in both tables

as seen on Stack Overflow - Search for 'Stack Overflow'
Table 1 Field1 Field2 AA 20 AA 20 AB 12 AC 13 Table2 field3 field4 AA 20 AA 20 AC 13 AD 23 AW 21 output required: newfield field2 field4 AA 20 20 AA 20 20 AC 13 13 I used: select field1 as newfield, t1.field2,t2.field4 from table1 t1 join table2 t2 on t1.field1=t2.field3 This… >>> More
Mulitple full joins in Postgres is slow

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a program to use the IMDB database and am having very slow performance on my query. It appears that it doesn't use my where condition until after it materializes everything. I looked around for hints to use but nothing seems to work. Here is my query: SELECT * FROM name as n1 FULL JOIN… >>> More

Related posts about hash

Problem with hash function: hash(1) == hash(1.0)

as seen on Stack Overflow - Search for 'Stack Overflow'
I have an instance of dict with ints, floats, strings as keys, but the problem is when there are a as int and b as float, and float(a) == b, then their hash values are the same, and thats what I do NOT want to get because I need unique hash vales for this cases in order to get corresponding values… >>> More
Hash table vs Hash list vs Hash tree?

as seen on Stack Overflow - Search for 'Stack Overflow'
What property makes Hash table, Hash list and Hash tree different from each other? Which one is used when? When is table superior than tree. >>> More
Constructing a hash table/hash function.

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I would like to construct a hash table that looks up keys in sequences (strings) of bytes ranging from 1 to 15 bytes. I would like to store an integer value, so I imagine an array for hashing would suffice. I'm having difficulty conceptualizing how to construct a hash function such that given… >>> More
Hash of unique value = unique hash?

as seen on Stack Overflow - Search for 'Stack Overflow'
Theoretically does hashing a unique value yield a unique value? Let's say I have a DB table with 2 columns: id and code. id is an auto-incrementing int and code is a varchar. If I do ... $code = sha1($id); ... and then store $code into the same row as $id. Will my code column be unique as well… >>> More
EMERGENCY - Major Problems After Perl Module Installed via WHM

as seen on Stack Overflow - Search for 'Stack Overflow'
I attempted to install the perl module Net::Twitter::Role::API::Lists using WHM and after doing so my whole site came down. It seems that something that was updated with the install isn't functioning correctly and since our website it written in Perl none of our site scripts will run. In almost 8… >>> More