RE: Histograms - SIZE clause & num_buckets anomaly (with a piggyback question)

  • From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Tue, 03 Aug 2004 10:17:23 -0600

You have a compressed HB histogram - one with popular values - if 
dba_tab_columns.num_buckets < max(dba_histograms.endpoint_number).
There is a slim theoretical chance that that condition is true for a 
frequency histogram, however, in general

num_buckets = 1 ( = max(endpoint_number) ==> no histogram
num_buckets = num_distinct-1 ==> frequency histogram
num_buckets = max(endpoint_number) ==> HB histogram without popular values 
( this includes case one, treating the entire value range as one big bucket)
num_buckets < max(endpoint_number) ==> HB histogram with popular values

At 06:33 AM 8/3/2004, you wrote:

>How to identify if the actual number of buckets is different from the value
>shown in NUM_BUCKETS column of USER_TAB_COLUMNS?
>Thanks & regards,


Wolfgang Breitling
Centrex Consulting Corporation 

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