How to reduce skew factor on stage tables with NoPI?

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How to reduce skew factor on stage tables with NoPI?

Hi,


 


I am new to teradata. I have several stage tables defined as NoPI.


I notice most stage talbes have skew factor > 50. Is there a way to reduce this.


What is the best way to handle this situation for stage tables with NoPI?


Any ideas. please advise.


 


Thanks,


VM.


22 REPLIES
Junior Apprentice

Re: How to reduce skew factor on stage tables with NoPI?

How large are those tables?


And how are they loaded?


Dieter


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Enthusiast

Re: How to reduce skew factor on stage tables with NoPI?

Hi VM,


 


These are probably small tables tables loaded with batch load TD utility.


Even though it is true that your NoPI tables will be loaded in round robin manner in this case, the round robin is applied on block level (not row level).


This implies that in the case of small tables that fit in one (a couple) of blocks, all the data will end up on a single (a couple) of AMPs. That should explain the high skew factor.


 


I would recommend distributing those tables on appropriate PI column.


You won't get any benefits on FastLoading a small NoPI table.


 


Cheers,


Igor


Re: How to reduce skew factor on stage tables with NoPI?

I have same problem.


My Table size 480 GigaByte and  skew factor > 78 . It is 7 column  table(Using 3 Column as primary Index).


I create also NoPI table but still skew factor is same.


 


How i reduce it ? Please help me.


Junior Supporter

Re: How to reduce skew factor on stage tables with NoPI?

If you created the NoPI table from the PI Table the skew will be the same (AMP local). You must create the NoPI table EMPTY and load it from scratch. This should guarantee a good distribution (e.g.: low skew).


HTH.


Cheers.


Carlos.


Junior Apprentice

Re: How to reduce skew factor on stage tables with NoPI?

In TD14 there's also a new option for INSERT/SELECT into NoPI tables, HASH BY RANDOM, to reduce skew.


 


Dieter


Re: How to reduce skew factor on stage tables with NoPI?

Hi,


I have a table in PRON which is having 3 Billion data. There are 4 Primary Index column, Partition on Date and secondary Index. when I checked the Distint Primary Indix on the combination of 4 columns. it is aboly 2.98 Billion. Percentage of duplicates is about 2%.


But the Skew in the table is 54. Can you plese explain how reduse the Skew factor.


 


Appriciate your help.


 


Thanks,


Manju


Enthusiast

Re: How to reduce skew factor on stage tables with NoPI?

Hi Manju,


Secondary index will not impact skew factor.


Skew factor can be reduced by choosing more evenly distributed set of columns. if your 2% is going to one amp then you can find out what distinguishs it in other columns from each other.


But reducing skew factor by choosing more appropriate Primary index column set will not help Teradata performance unless it is used in SQLs. Primary index needs to be mostly usable in sqls as whole and not partially and nearly evenly distributed.


Thanks


Harpreet


Re: How to reduce skew factor on stage tables with NoPI?

Thanks Harpeet ...


Enthusiast

Re: How to reduce skew factor on stage tables with NoPI?

hi 


can we take a column which is declare as compress(0) as PI  column.


max how many column we can go for combination  to find better pi for skew