# Re: Statistics Problem on partitioned table

Date: Wed, 2 Oct 2013 12:55:39 +0100

Message-ID: <04AFAC43D78D4E79AB8DC5E81821C2E2_at_Primary>

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) . Thats 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.*

*>*

*>*

-- http://www.freelists.org/webpage/oracle-lReceived on Wed Oct 02 2013 - 13:55:39 CEST