Oracle-L: RE: Burned by DBMS

From: Jesse, Rich <Rich.Jesse_at_qtiworld.com>
Date: Wed, 09 Apr 2003 11:24:04 -0800
Message-ID: <F001.0057E4B9.20030409112404@fatcity.com>

I tried to see if that was indeed the issue by saving SYS.HIST_HEAD$ after an ANALYZE and repopulating the DENSITY column after rebuilding the stats with DBMS_STATS, but the explain plan of the icky SQL in question didn't change. I then tried doing the same with the remaining columns that differ in HIST_HEAD$ between ANALYZE and DBMS_STATS -- BUCKET_CNT, SAMPLE_SIZE, MINIMUM, MAXIMUM, SPARE2, and AVGCLN -- but no change in results.

So, without further hacking, I think I'm left with using ANALYZE for the forseeable future.

Did I mention a new/improved query in this 3rd party app? They added an ORDERED hint causing a 7-sec query to now blow up after using all 2GB of TEMP available. The explain plan estimates TEMP usage at about 29GB on a MERGE SORT CARTESIAN (if I interpreted it correctly)...

Thank God tomorrow's Beer Day at the Beer Ale Lager Lovers Society! :9 http://society.servebeer.com

Rich

Rich Jesse                        System/Database Administrator
rich.jesse_at_qtiworld.com           Quad/Tech International, Sussex, WI USA

-----Original Message-----
Sent: Wednesday, April 09, 2003 10:54 AM To: Multiple recipients of list ORACLE-L

A-ha....now try the same thing with a column that is NULL in all rows.

There's one difference between ANALYZE and DBMS_STATS, but I'm not sure if that accounts for the explain plan diffs I'm seeing. It would account for the fact that I wasn't seeing any of those columns in DBA_IND_COLUMNS for this particular schema though.

Stay tuned to this thread for further developments.

Rich

Rich Jesse                        System/Database Administrator
rich.jesse_at_qtiworld.com           Quad/Tech International, Sussex, WI USA

"AAAAAAAAAAAAAAAAAAAAAAAAAAAUGH!  Tension breaker, had to be done."
          -- Chainsaw
             Summer School

-----Original Message-----
Sent: Tuesday, April 08, 2003 5:09 PM
To: Multiple recipients of list ORACLE-L

I've just checked on my 8.1.7.4

create table t1 (n1 number, v1 varchar2(10)); create index t1_idx on t1(n1);

insert into t1
select rownum rownum
from all_objects
where rownum <= 100;

analyze table T1 compute statistics;

select * from user_tab_histograms
where table_name = 'T1';

This gives me two rows each
for N1 and V1.

Similarly

select low_value, high_value
from user_tab_columns
where table_name = 'T1';

gives me one row for each column,
with the high and low value set.

analyze table XXX compute statistics;

should be the equivalent of

'for table for ALL columns size 1';

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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Author: Jesse, Rich
INET: Rich.Jesse_at_qtiworld.com

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RE: Burned by DBMS_STATS **AGAIN**

RE: Burned by DBMS_STATS AGAIN