RE: Histograms

  • From: "Marquez, Chris" <cmarquez@xxxxxxxxxxxxxxxx>
  • To: <charlottejanehammond@xxxxxxxxx>, "ORACLE-L" <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 16 Aug 2005 16:51:50 -0400

One DBA decided "based one an Oracle guru article" to start collecting a
lot of Histograms.
Despite other serious performance problems ("cursor_sharing" & "variable
peaking", resolved by member of this list, thanks Wolfgang Breitling)
we also ran into a nasty "failed to extend" on an internal sys table.
We ere previously getting extend errors (all day).

Seems that all this Histograms stuff has to be stored somewhere.
We have a 4k block size and originally a 8i database upgrade migrated to
This is important because this information drives the extent setting on
some/many/all internal tables.

The funny/sad thing is when I went to Metalink the problem was described
as improper DBA space allocation.
Funny...I don't remember my job requiring me to establish extent
parameters for internal Oracle tables.

What do you think the fix was...I think if was ALTERing *and* UPDATEing
internal tables to allow this table to have *more* extents....this
required a (short) outage and came with "you been warned" warning form
Oracle...oh joy. :o|

I like being a DBA but take no pleasure in mucking with internal tables.

Oh yeah, the guru left the overhead and potential issues out of his


Chris Marquez
Oracle DBA

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Charlotte Hammond
Sent: Tuesday, August 16, 2005 7:34 AM
Subject: Histograms

Hi All,

Can I poll the list on their views on the use of histograms?  I've
previously been quite conservative, only gathering them when we've had a
specific case of bad CBO performance due to skewed data.  However I was
interested in this article mentioning a "broad brush"
approach to histogram gathering:

Any thoughts to share?

Thank you

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