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08-27-2008
07:53 AM

08-27-2008
07:53 AM

hi

what is skew factor????? what is the use of that?

what is skew factor????? what is the use of that?

22 REPLIES

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08-27-2008
01:08 PM

08-27-2008
01:08 PM

Hello,

Skewness is the statistical term, which refers to the row distribution on AMPs. If the data is highly skewed, it means some AMPs are having more rows and some very less i.e. data is not properly/evenly distributed. This affects the performance/Teradata's parallelism. The data distribution or skewness can be controlled by choosing indexes.

HTH.

Regards,

Adeel

Skewness is the statistical term, which refers to the row distribution on AMPs. If the data is highly skewed, it means some AMPs are having more rows and some very less i.e. data is not properly/evenly distributed. This affects the performance/Teradata's parallelism. The data distribution or skewness can be controlled by choosing indexes.

HTH.

Regards,

Adeel

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08-28-2008
08:49 AM

08-28-2008
08:49 AM

thx

how 2 find out skew value?

how 2 find out skew value?

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08-28-2008
10:09 AM

08-28-2008
10:09 AM

Try something like:

SELECT TSIZE.DatabaseName

,TSIZE.TableName

,TDEF.CreateTimeStamp AS Created

,TDEF.LastAlterTimeStamp AS LastAltered

,TDEF.AccessCount

,TDEF.LastAccessTimeStamp AS LastAccess

,SUM(TSIZE.CurrentPerm) AS CurrentPerm

,SUM(TSIZE.PeakPerm) AS PeakPerm,

(100 - (AVG(TSIZE.CurrentPerm)/MAX(TSIZE.CurrentPerm)*100)) AS SkewFactor

FROM DBC.TableSize TSIZE

JOIN DBC.Tables TDEF

ON TSIZE.DatabaseName = TDEF.DatabaseName

AND TSIZE.TableName = TDEF.TableName

GROUP BY 1,2,3,4,5,6;

Lower the skew factor the better - although if you have only a very few rows on a table you are going to have a skewed table no matter what!

SELECT TSIZE.DatabaseName

,TSIZE.TableName

,TDEF.CreateTimeStamp AS Created

,TDEF.LastAlterTimeStamp AS LastAltered

,TDEF.AccessCount

,TDEF.LastAccessTimeStamp AS LastAccess

,SUM(TSIZE.CurrentPerm) AS CurrentPerm

,SUM(TSIZE.PeakPerm) AS PeakPerm,

(100 - (AVG(TSIZE.CurrentPerm)/MAX(TSIZE.CurrentPerm)*100)) AS SkewFactor

FROM DBC.TableSize TSIZE

JOIN DBC.Tables TDEF

ON TSIZE.DatabaseName = TDEF.DatabaseName

AND TSIZE.TableName = TDEF.TableName

GROUP BY 1,2,3,4,5,6;

Lower the skew factor the better - although if you have only a very few rows on a table you are going to have a skewed table no matter what!

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08-28-2008
12:21 PM

08-28-2008
12:21 PM

In Teradata Administrator you can simply right-click the table and select "Space Summary".

Regards,

Adeel

Regards,

Adeel

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08-26-2009
01:44 AM

08-26-2009
01:44 AM

What is a acceptable Skew Factor ? Say if one of my table is having skew factor of 16. Is it acceptable?

--Thanks in advance.

--Thanks in advance.

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11-23-2010
04:31 PM

11-23-2010
04:31 PM

how to check the skew factor?

suppose i use Primary index that situation how to distributes the row?

suppose i use unique Primary index that situation how to distributes the row?

normally if we u PI then data will distribute evenly thats not an issue

if we use UPI then how we have to distributes the records evenly

suppose i use Primary index that situation how to distributes the row?

suppose i use unique Primary index that situation how to distributes the row?

normally if we u PI then data will distribute evenly thats not an issue

if we use UPI then how we have to distributes the records evenly

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11-23-2010
07:16 PM

11-23-2010
07:16 PM

Hi,

how to distributes the row in mload if we use UPI and how in fload if we use UPI and how if we use NUPI

and finally i have to distributes the row evenly to all AMPs for best skew factor,

any one which best way to distribute the row evenly in mload and fload when we use UPI and NUPI

how to distributes the row in mload if we use UPI and how in fload if we use UPI and how if we use NUPI

and finally i have to distributes the row evenly to all AMPs for best skew factor,

any one which best way to distribute the row evenly in mload and fload when we use UPI and NUPI

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02-27-2011
10:00 AM

02-27-2011
10:00 AM

Skew facter is tell the distribution of rows

if uniformally distribution i.e skew is the zero

if the skew factor is reverse of parllel efficence

if uniformally distribution i.e skew is the zero

if the skew factor is reverse of parllel efficence

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11-04-2014
12:15 PM

11-04-2014
12:15 PM

Hi,

Below is the query which is usefull to find out skewfactor.

`SELECT `

`TABLENAME,`

`SUM(CURRENTPERM) /(1024*1024) AS CURRENTPERM, `

`(100 - (AVG(CURRENTPERM)/MAX(CURRENTPERM)*100)) AS SKEWFACTOR `

`FROM `

`DBC.TABLESIZE `

`WHERE DATABASENAME= <DATABASENAME> `

`AND `

`TABLENAME =<TABLENAME> `

`GROUP BY 1;`

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