Oracle-L: RE: Statistics - using dbms

From: Grabowy, Chris <cgrabowy_at_fcg.com>
Date: Thu, 08 Aug 2002 12:19:37 -0800
Message-ID: <F001.004AFAEC.20020808121937@fatcity.com>

Hi Raj,

I am assuming that you are using DBMS_STATUS.GATHER_SCHEMA_STATUS, so perhaps you are not generating stats for the indexes. The syntax...

DBMS_STATS.GATHER_SCHEMA_STATS (
ownname VARCHAR2,
estimate_percent NUMBER DEFAULT NULL,

   block_sample     BOOLEAN  DEFAULT FALSE,
   method_opt       VARCHAR2 DEFAULT 'FOR ALL COLUMNS SIZE 1',
   degree           NUMBER   DEFAULT NULL,
   granularity      VARCHAR2 DEFAULT 'DEFAULT', 
   cascade          BOOLEAN  DEFAULT FALSE);

The last parameter is "cascade", which determines if stats are generated for indexes. As you can see, the default is FALSE.

If you are using DBMS_STATS.GATHER_SCHEMA_STATS then are you setting the cascade parameter to TRUE?

Also, if your only populating the first two parameters, then you may want to look over all the parameters. Everyone of them may have some potential value for your situation.

HTH Chris

-----Original Message-----
Sent: Thursday, August 08, 2002 2:49 PM
To: Multiple recipients of list ORACLE-L

Okay ... here is the problem ...

We have our DB (8161) running in RULE mode. Due to some schema using Context, we need to analyze a bunch of tables, but the table has optimizer mode set to RULE.

We used to do 'exec dbms_utility.analyze_schema('<schema>,'COMPUTE');' for a long time. Lately it doesn't finish, so I changed it to ESTIMATE. The database and certain queries were okay, running within limits.

Then one day (my mistake), I changed the scripts to use dbms_stats to do the analyze instead of dbms_utility.analyze_schema. This broke some of our critical and large reports. These reports run in 20 mins, but after using dbms_stats, it took the reports > 2.5 hours to finish.

I assume, dbms_utility.analyze_schema(), 'alter table analyze', and dbms_stats are same and do the same thing. So, why do the reports work fine when using the former 2 and a re dead slow when using dbms_stats ?? What is so different in 'analyze table' and 'dbms_stats' ??

Any hints, ideas are gratefully accepted.

Thanks in advance
Raj

Rajendra Jamadagni MIS, ESPN Inc.
Rajendra dot Jamadagni at ESPN dot com
Any opinion expressed here is personal and doesn't reflect that of ESPN Inc.

QOTD: Any clod can have facts, but having an opinion is an art!

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Author: Grabowy, Chris
INET: cgrabowy_at_fcg.com

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RE: Statistics - using dbms_stats breaks the query