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Message Posted: Thu, 01 Mar 2013 @ 01:39:40 GMT


     
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Subj:   Re: Tables: How small is small for TD to dynamically
 
From:   Attila_Finta

Ken Hansen wrote:
  I have a question regarding PI definition for small tables. Teradata replicates small tables across all AMPs (when joined to another table having a different PI). Therefore we have been recommending that small tables should have a Unique PI that is the same as the PK (to maximize even distribution). For larger tables I believe we must also consider frequent access points and join paths. Do you have any guidance re: "how small is small"? How small is small enough for TD to replicate the table? 1 MB? 10 MB?  


  When joining two tables with different PIs, Teradata will replicate and redistribute the smaller of the two - irrespective of size but success will depend upon the size of available spool space.  


Thanks Ken. Isn't it "replicate OR redistribute"? Aren't those are two very different things? My understanding is that a small code table will replicated to all AMPs in its entirety (all rows copied to all AMPs) while for a large table (still the smaller one in the join) each of its joining rows will be redistributed to the single appropriate AMP. So the point of my question is: what's that threshold? Or what am I misunderstanding?


Attila Finta



     
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