RE: Any quick way to remove histograms?
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: Brandon.Allen@xxxxxxxxxxx
- Date: Tue, 27 Mar 2007 07:19:36 -0600
Why spool, capture and then execute when you can do it all in one:
declare
l_ndv number;
l_dummy number;
l_srec dbms_stats.statrec;
begin
for r in (select owner, table_name, column_name, null
partition_name from DBA_TAB_COL_STATISTICS
histogram <> 'NONE' [ and possibly other criteria ]
union all
select owner, table_name, column_name, partition_name from
DBA_PART_COL_STATISTICS
histogram <> 'NONE' [ and possibly other criteria ]
) loop
dbms_stats.get_column_stats (
ownname => r.owner,
tabname => r.table_name,
colname => r.column_name,
partname => r.partition_name,
stattab => null,
statid => null,
distcnt => l_ndv,
density => l_dummy,
nullcnt => l_dummy,
srec => l_srec,
avgclen => l_dummy);
dbms_stats.set_column_stats (
ownname => r.owner,
tabname => r.table_name,
colname => r.column_name,
partname => r.partition_name,
distcnt => l_ndv);
end loop;
end;
and no fighting with quotes :-)
I believe if you have subpartitions you will need to export the
statistics to a stattab table, manipulate the statistics there and
then re-import as there is no set_column_stats for subpartitions.
At 06:23 PM 3/26/2007, Allen, Brandon wrote:
At first I was thinking that Alberto's procedure would still be required
for retrieving the current stats and then resetting just the distcnt
value. However, after thinking it through for a while, I realized what
you were probably both thinking the whole time, which is that with this
simplified method, you can just use a simple SELECT statement on
all_tab_col_statistics to retrieve the current num_distinct value and
plug it into the set_column_stats procedure for all columns that
currently have histograms, thereby creating a script that can be used to
very quickly remove all existing histograms. It took me a while to get
all the single quotes just right, but here is the working version for
anyone else that might find it helpful:
select 'execute dbms_stats.set_column_stats(''' || owner || ''',''' ||
table_name || ''',''' || column_name || ''', distcnt=>''' ||
num_distinct || ''');' from all_tab_col_statistics where histogram <>
'NONE';
Sample Output:
----------------------------------------------------------------------
execute dbms_stats.set_column_stats('SCOTT','T','C1', distcnt=>'2421');
execute dbms_stats.set_column_stats('SCOTT','T','C2', distcnt=>'2425');
execute dbms_stats.set_column_stats('SCOTT','T','C3', distcnt=>'2421');
Thanks again to Wolfgang and Alberto!
Regards,
Brandon
-----Original Message-----
From: Alberto Dell'Era [mailto:alberto.dellera@xxxxxxxxx]
Sent: Friday, March 16, 2007 4:43 PM
To: breitliw@xxxxxxxxxxxxx
Cc: Allen, Brandon; Oracle-L@xxxxxxxxxxxxx
Subject: Re: Any quick way to remove histograms?
Much simpler :) - interesting.
On 3/16/07, Wolfgang Breitling <breitliw@xxxxxxxxxxxxx> wrote:
>
> I also did a quick check and just using
>
> exec
> dbms_stats.set_column_stats(user,'table_name',colname=>'column_name',d
> istcnt=>
> <num_distinct>);
>
> will remove the histogram without removing the low_value and
high_value.
>
>
>
> At 01:40 PM 3/16/2007, Alberto Dell'Era wrote:
> >On 3/16/07, Allen, Brandon <Brandon.Allen@xxxxxxxxxxx> wrote:
> >>Is there any faster way to remove histograms other than re-analyzing
> >>the table? I want to keep the existing table, index & column stats,
> >>but with only 1 bucket (i.e. no histograms).
> >
> >You might try the attached script, that reads the stats using
> >dbms_stats.get_column_stats and re-sets them, minus the histogram,
> >using dbms_stats.set_column_stats.
> >
> >I haven't fully tested it - it's only 10 minutes old, even if I have
> >slightly modified for you another script I've used for quite some
> >time - and the spool on 10.2.0.3 seems to confirmthat the histogram
> >is, indeed, removed, while all the other statistics are preserved. I
> >have also reset density to 1/num_distinct, that is the value you get
> >if no histogram is collected.
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Regards
Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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