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$.
During normal operations, it's SMON who's doing that over regular
intervals.
You can disable collecting these statistics by
setting _column_tracking_level to 0.
I don't really see where CBO could use those
statistics for speeding up statement execution, because during execution CBO
knows all the predicates & statement structure anyway. But it is probably
useful for various 10g's advisories, which can make you recommendations based on
how the tables (columns) are used. Also, it might help automatic statistics
gathering to determine which stats need to be updated or not (this gather stale
stuff).
Tanel.
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Title: col_usage$ question
- col_usage$ question Jamadagni, Rajendra
- Re: col_usage$ question Wolfgang Breitling
- RE: col_usage$ question K Gopalakrishnan
- RE: col_usage$ question Jamadagni, Rajendra
- RE: col_usage$ question Jamadagni, Rajendra
- Re: col_usage$ question Tanel Poder
- Re: col_usage$ question Daniel Fink
- Re: col_usage$ question Wolfgang Breitling
- Re: col_usage$ question Wolfgang Breitling
- Re: col_usage$ question Binley Lim
- RE: col_usage$ question Jamadagni, Rajendra