Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people, just like you, are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
Solved

hash partition

Posted on 2011-03-16
3
665 Views
Last Modified: 2012-05-11
Is a hash partition better suited for a table's column with high or low cardinality?
0
Comment
Question by:msimons4
  • 2
3 Comments
 
LVL 48

Accepted Solution

by:
schwertner earned 500 total points
ID: 35148826
Oracle says:

Hash partitioning maps data to partitions based on a hashing algorithm that Oracle applies to the partitioning key that you identify. The hashing algorithm evenly distributes rows among partitions, giving partitions approximately the same size.

Hash partitioning is the ideal method for distributing data evenly across devices. Hash partitioning is also an easy-to-use alternative to range partitioning, especially when the data to be partitioned is not historical or has no obvious partitioning key.

My comment is that if you have big amount of data that is randomly used you can spread the data on different disk devices to reduce the contention. But if you can somehow to range the data and the select statements in your application use data grouped in ranges, intervals and so on the hash partitioning is not a good decission.

The cardinality can affect the hash partitioning only by high cardinality. In this case if you select rows thre is no waranty that they sit in same partition. So spreading them on different devices can paralelize the query and be winning.

But if you can group the rows belonging to one search criteria in one partition - this will be the best solution. But this is range hashing.....
0
 

Author Comment

by:msimons4
ID: 35148886
Range hashing is not an option since there is no range in the search condition. So I have this table with 45 columns, do I list every column in the hash partition or do I list the columns in the index or do I list the columns in the PK ect? How do I determine which columns to list in the hash partition?
0
 
LVL 48

Assisted Solution

by:schwertner
schwertner earned 500 total points
ID: 35151658
The index(es) depend(s) on the select statement(s) you use.

The primary key (PK) is a must if this is not a datewarehouse.
In OLTP is row has to have PK. Even in DW the rows have to have PK because references will be almost impossible.
0

Featured Post

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
PL/SQL Two changes 7 34
Creation date for a PDB 5 39
sum of columns in a row in oracle 3 32
why truncate is faster than delete in oracle ? 4 20
Checking the Alert Log in AWS RDS Oracle can be a pain through their user interface.  I made a script to download the Alert Log, look for errors, and email me the trace files.  In this article I'll describe what I did and share my script.
From implementing a password expiration date, to datatype conversions and file export options, these are some useful settings I've found in Jasper Server.
This videos aims to give the viewer a basic demonstration of how a user can query current session information by using the SYS_CONTEXT function
This video explains what a user managed backup is and shows how to take one, providing a couple of simple example scripts.

808 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question