Archives of the TeradataForum
Message Posted: Thu, 03 Aug 2006 @ 17:32:51 GMT
| Subj: | | Re: Recommendations from Statistics Wizard |
| |
| From: | | Victor Sokovin |
| | Does anyone know where is the sampling rate is held, nothing obvious in the dbs control settings? | |
I might have got confused when I mentioned the DBS settings. They can influence the random AMP sample, not the All-AMPs sample, which you are
using. The rate of the latter is dynamically increased if the data is skewed so perhaps skewing it even further is the way to go. Just
kidding.
| | I presume that the sampling also has an impact on the min and max values that the stats usual gather for the column? | |
Yes, it has impact on everything.
| | For info, the table being used is a 6.5 billion row table and the column having the stats amended is a PPI column for the
table. | |
I think some posters might have been confused by your earlier statement (perhaps it was somebody else's statement; hard to tell as it was
anonymously posted):
"However, on some columns on a few very small tables, the recommendation came out as "Collect Statistics Using Sample... ." on some
of the columns/Indexes. In fact, some columns in these same tables were implemented as "using Sample" while others were implemented as using the
entire population (without sampling). All recommendations for a given table were made and implemented on the same day."
800 unique values was also creating an idea of something small but it turned out that to this cute little head chewing on the green
bushes quite a dinosaur was attached.
How many AMPs does your system have? Do you know the skew rate for the table? It might be interesting to understand the math behind this case
but we need to know more about the table definition and data distribution.
Regards,
Victor
| 
