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Message Posted: Mon, 17 Mar 2008 @ 23:48:45 GMT


     
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Subj:   Re: Creating a table with a 0 skew factor
 
From:   Curley, David

You don't say how many rows you inserted, but if it's less than the number of AMPs, the table can't help but be skewed.

I've heard from a couple people that UPIs can't be skewed, but nobody's actually been able to explain why. On the other hand, it's trivial to create a highly skewed UPI table, so perhaps I just misheard them. Maybe they just meant it's unlikely.

I'm curious about why you're doing this in the first place, though. You paid how much for this disk space and you're going to lock it away? Maybe your local powers that be would also want stop users from submitting queries - that should keep a lot of CPU available, too ;) Why not just allocate space to a new database and leave it empty so it's available for spool, then reallocate it if you need it for data?

If you really wanted to make it non-skewed and you knew the total number of rows you wanted, base it off an existing big table. Say you wanted 100 rows on each AMP:

     insert into COD_1 (seq_no)
     select rn
     from
     (select row_number() over (order by 1) rn
     from some_big_table) list_of_rn
     qualify row_number() over (partition by hashamp(hashbucket(hashrow(rn)))
     order by rn) < 101

Dave



     
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