Oracle-L: RE: col_usage$ question

From: Jamadagni, Rajendra <Rajendra.Jamadagni_at_espn.com>
Date: Wed, 19 Nov 2003 05:20:00 -0800
Message-ID: <F001.005D728C.20031119052000@fatcity.com>

Thanks Tanel,

I also found that whenever one issues dbms_stats.flush_database_monitoring_info(), it updated some info in col_usage$ as well with mon_mods$ of course. That's where I found this reference and hence my original email.

Thanks everyone.

I am currently working on a test to prove that pipelining doesn't work as advertised in some cases (... only if I could get some free time to finish the test). Raj

Rajendra dot Jamadagni at nospamespn dot com All Views expressed in this email are strictly personal. QOTD: Any clod can have facts, having an opinion is an art !

-----Original Message-----
Sent: Tuesday, November 18, 2003 1:04 PM To: Multiple recipients of list ORACLE-L

Hi!

If you describe this table then you see that this table stores column usage information in filter and join predicates for database objects. From describe, you see there are several filter and join conditions tracked for an object's (obj#) columns (intcol#). You can join them to col$ table for example.

During shutdown, the session executing shutdown, writes the column usage statistics to col_usage$. During normal operations, it's SMON who's doing that over regular intervals.

You can disable collecting these statistics by setting _column_tracking_level to 0.

I don't really see where CBO could use those statistics for speeding up statement execution, because during execution CBO knows all the predicates & statement structure anyway. But it is probably useful for various 10g's advisories, which can make you recommendations based on how the tables (columns) are used. Also, it might help automatic statistics gathering to determine which stats need to be updated or not (this gather stale stuff).

Tanel.

Original Message ----- To: Multiple recipients of list ORACLE-L <mailto:ORACLE-L_at_fatcity.com> Sent: Tuesday, November 18, 2003 6:29 PM

Does anyone know what this table (sys.col_usage$) is used for? To me it sounds like something that CBO might appreciate ... but any ideas? It is referenced by dbms_stats and dbms_stats_internal packages ...

Thanks in advance
Raj

Rajendra dot Jamadagni at nospamespn dot com All Views expressed in this email are strictly personal. QOTD: Any clod can have facts, having an opinion is an art !

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Author: Jamadagni, Rajendra
  INET: Rajendra.Jamadagni_at_espn.com

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Received on Wed Nov 19 2003 - 07:20:00 CST