Re: Partitioning

Rishi.Jain_at_VerizonWireless.com wrote:
>
> We have a table with around 80 million rows. The table has been partitioned
> by hash as there is no clear way of partitioning depending on range etc..
> The data is very unevenly distributed in these partitions. Some of them even
> have 3 times the number of rows as compared to the other partitions.
> This application is being ported from Informix to Oracle (9i R2). In
> informix the dba's had partitioned the table based on a function . He was
> taking the mod of the number ( dividing by 10 ) . The values were then
> placed in either of the 10 partitions ranging from 0 - 9. This really gave
> us very good distribution of data .Can we achieve something similar in 9i
> with list partitioning.
>
> TIA
>
> Rishi
> --

I have recently met a similar problem. The risk with hash partitioning and a skewed distribution is that a low cardinality key hashes into the same value as a high cardinality one. Bad for the rows with the low cardinality key. What you should do is to decide first how many partitions you want, and what keys you want together. Then find a way, whether it is range or list partitioning, to have the corresponding rows stored where they should. Hash partitioning is fine, but when the distribution is more or less uniform.  

HTH, Stephane Faroult
Oriole Software

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Author: Stephane Faroult
  INET: sfaroult_at_oriole.com

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