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11 Oct 2006
whether row hash changes when new nodes or Amp added?

Hi All, As I am going to prepare for PI and puzzled in few questions, looking to find the answer of these questions...whether hash row changes when we add new AMPs or Nodes in the existing Teradata System....?can any body put more lights on it....Thanks in Advance....

John Mac 21 posts Joined 11/05
11 Oct 2006

If you do a reconfig, you'll get a new Hashmap

Jim Chapman 449 posts Joined 09/04
11 Oct 2006

The hash map is recomputed when the AMP configuration changes, but the hashing function itself is independent of the configuratiion. In other words, row hash values do not change.

SarathyG 31 posts Joined 09/06
12 Oct 2006

RowHash is getting generated from the Primary Index value. Given the Primary Index value to the Hashing Algo, it will generate the row hash. So, RowHash is always dependant on the primary index value, and it has nothing to do with the number of AMPs. However, whenever the number of AMPs get increased/decreased, the HashMap size is getting adjusted accordingly to accomadate the currect number of AMPs.Hope solved your doubt.

- Sarathy G

13 Oct 2006

hithanks all for replying.... it is more clearer to me....Thanks......

chezian 2 posts Joined 02/12
15 Feb 2012

hi

Does Row hash for a PI value changes as and when its datatype changes?

ulrich 816 posts Joined 09/09
15 Feb 2012

Yes for real data type changes like char to integer.

And smallint and integer values are hashed the same (for smallint range)

Check the outcome of hashrow 

 

select hashrow(cast('123' as char(10)))

 

select hashrow(cast('123' as varchar(100)))

 

select hashrow(cast('123' as integer))

 

subt["select hashrow(cast('123' as smallint))"]

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