fastload to NOPI table gives skew

Database
Teradata Employee

fastload to NOPI table gives skew

a large table created with a NOPI is loaded with more than 1.000.000.000 rows to a 6800 system with 126 AMPs.

88 AMPS have much more data than the other 38, for example the first 4 AMPS give:

TableName VPROC CurrentPerm

CCT001HND 0      197.323.776

CCT001HND 1   2.246.341.632

CCT001HND 2      197.011.968

CCT001HND 3  2.246.341.632

..

The same pattern occurs with similar NOPI tables loaded.

When a copy is made of the table with CREATE TABLE XX AS CCT001HND WITH DATA suddenly all AMPs have around the same space (about 2.246.xxx.xxx currentperm)

How is this possible ? Is there some kind of compression when loading the data ? is something wrong with the currentperm figure with NOPI tables ? How do you check the number of rows per AMP with a NOPI table ?

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3 REPLIES
Teradata Employee

Re: fastload to NOPI table gives skew

-----------+-----------+
|            |Compr-|Estimated |Estimated % |                      Distribution of data block sizes                       |   Data block    |   Total    |   Total   |
|            |ession| Compres- | of Blocks  |                       (by range of number of sectors)                       | size statistics |   Number   |   Number  |
|  Table ID  |Status|  sion    |   Un-      +----+----+----+----+----+----+----+----+----+----+----+----+-----+-----+-----+    (sectors)    |     of     |     of    |
|            |      |  Ratio   | compressed |  1-|  9-| 25-| 65-|121-|169-|217-|257-|361-|457-|513-|761-|1025-|1305-|1633-|-----+-----+-----+    Data    | Cylinders |
|            |      |          |            |  8 | 24 | 64 |120 |168 |216 |256 |360 |456 |512 |760 |1024|1304 |1632 |2048 | Min | Avg | Max |   Blocks   |           |
|    0  5560 |  PC  |  90.45%  |  79.53%    |    |    | 30%|    |    |    |    |    |    | 70%|    |    |     |     |     |   4 | 371 | 512 |   1079883  |     19224*|
+------------+------+----------+------------+----+----+----+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+------------+-----------+
* Reported in units of Large Cylinders
  (A Large Cylinder is 6 times the size of a small cylinder)

 "Compression Status" :  C = Fully Compressed
                        PC = Partially Compressed
                         U = Fully Uncompressed
                         N = Not Compressible

This is the ferret showblocks output.. There seem to be data compressed

But difficult to see why only 38 AMPs are compressed

Teradata Employee

Re: fastload to NOPI table gives skew

Executing UpdateSpace and checking again would allow determination whether it is a space accounting issue. 

I suggest opening a teradata incident in any case. Skew is expected if the table is small but in a table this size it should be quite evenly distributed. 

Junior Supporter

Re: fastload to NOPI table gives skew

Hi.

>>"But difficult to see why only 38 AMPs are compressed"

Temperature-based block-level compression perhaps?

Cheers.

Carlos.