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Forum Newbie
Group: Forum Members
Last Login: 4/8/2008 3:12:17 PM
Posts: 2,
Visits: 11
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We've a SET table defined with a UPI that has 9.3 Million rows on a 1400 AMP, V2R6 Teradata system. Please look at the numbers below. The AMP that has the MAX rows has 3.47 times more rows than the AMP with the MIN rows. This does not make sense to me given the fact that we've a UPI and a high volume of rows in the table for an even distribution.
xTimesGreaterMaxAvg - 1.56
xTimesGreaterMaxMin - 3.47
Mx - 1393664
Avrg - 890657.07
Mn - 401920
CurPerm - 1282546176
Can someone please shed some light on this? Is there something we can look at to improve data distribution? Any help would be greatly appreciated.
PS: The table also has a PPI defined on a date field which is part of the UPI (if this matters).
Thanks,
Sayee.
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Sayee
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Supreme Being
Group: Forum Members
Last Login: Yesterday @ 9:37:55 AM
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Hi Sayee,
most of the skew is due to the high number of AMPs:
There are 65536 entries within the hashmap, so the average number of entries per AMP is:
SELECT 2**16/1400 -> 46,81
Of course there's no .81 entry, so some AMPs will get 46 and some 47:
SELECT 47/46.0000 -> 1,0217 -> 2.17 percent more data even if there's a UPI.
Now the table is still small (for a 1400 AMP system), 6642 rows per AMP in average, this is probably not enough for a perfectly even distribution. Now add this small skew to the 2.17 percent...
Dieter
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Forum Newbie
Group: Forum Members
Last Login: 4/8/2008 3:12:17 PM
Posts: 2,
Visits: 11
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Thank you, Dieter! That was pretty good information. I never would have thought 9MM rows was not enough volume. :-)
We've more than 1 day's data in those tables now and we're seeing much better numbers (distribution).
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Sayee
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