Re: Statistics Problem on partitioned table

Okay - got it.

The simple answer is that you're missing a histogram (or the histogram that Oracle acquired id garbage.
Most efficient trick - you've run the query about which values appear how often - create a frequency histogram for the 250 most popular (or less if appropriate), include the low and high values put in one extra value with the number of rows x 2 that you want the optimizer to consider for all other values then call set_table_stats.

See my latest article for allthingsoracle - published about 24 hours ago, by coincidence.

Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com/all-postings

Author: Oracle Core (Apress 2011)
http://www.apress.com/9781430239543

• Original Message ----- From: "Mohamed Houri" <mohamed.houri_at_gmail.com> To: "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> Cc: "ORACLE-L" <oracle-l_at_freelists.org> Sent: Wednesday, October 02, 2013 12:39 PM Subject: Re: Statistics Problem on partitioned table

Jonathan,

I am sorry I may have not been clear but there are in fact 721,699 and that is what I showed above

 *select per_ind, count(1) cnt from XXX_PER_YYY group by per_ind;*

721,699 rows …

   PER_IND CNT

• ----------

14820567 2

14820568 2

14823592 2

14888565 2

14332136 2

13565375 2

 13617240 2

…

 13546549 92

  13546573 92

  13546630 92

  13546881 92

  13546890 92

  13546911 92

…

  13546914 92…

….

And so on until I arrived at the end (721,699)

13831389 130

13831395 130

13831404 130

13831451 130

0                            6119655   ----> this is my predicate

It is when I count how many distinct CNT I have that I found 59 rows (2, 92, 130, .......6119655) . That’s what I meant by 59 rows

Best regards

2013/10/2 Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>

>
> Mohamed,
>
>
>
> There's still the puzzle that you now show 56 distinct values, but the
> stats show 721,599 distinct keys.
>
> We need to work out how this discrepancy could have appeared (it would
> explain your plan, of course).
>
>
>
> Regards
>
> Jonathan Lewis
>
>
>
>
>
> ________________________________
> From: Mohamed Houri [mohamed.houri_at_gmail.com]
> Sent: 02 October 2013 09:58
> To: Jonathan Lewis
> Cc: ORACLE-L
> Subject: Re: Statistics Problem on partitioned table
>
>
> Jonathan
>
> > How come there is only one distinct value of per_ind (first post), but
> the number of distinct keys in the index on per_ind is over 700,000 ?
>
> Again nicely spotted. Here below is the correct figure
>
> select per_ind, count(1) cnt from XXX_PER_YYY group by per_ind;
>
> 721,699 rows …
>
> I managed to put the result in a test table so that I can check how much
> count I have for each per_ind and so on
>
> select distinct cnt from mho_test order by cnt asc;
>
> 2
>
> 4
>
> 6
>
> 8
>
> 10
>
> 12
>
> 14
>
> …
>
> 6119655 ---> this the count for per_ind = 0 (at the moment the query was
> issued)
>
> 56 rows
>
>
> The old figure (that have prompted your question) was against a view
> XXX_PER_YYY_VW (which is select * from XXX_PER_YYY where per_ind = 0).
>
>
> There 4 columns on the XXX_PER_YYY table and they are all not null;
>
> SQL> select count(1)
>
> from
>
> (
>
> select table_name, partition_name, global_stats, last_analyzed,
> num_rows
>
> from all_tab_partitions
>
> where table_name='XXX_PAR_YYY’
>
> )
>
> where num_rows = 0;
>
>
>
> COUNT(1)
>
> ----------
>
> 758
>
>
>
> 785 empty partitions over 1493 partitions.
>
>

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