Matt,
Histograms can cause the optimizer to make some really bad or really good
decisions. Histograms are good for SQL statements that use literals but
can be detrimental for systems that use binds. (They can also be good for
systems that use binds if the data is evenly distributed between stored
values).
So, histograms are not always bad and are not always good either. You have
to really be aware of them when performance tuning as they could be helping
you or killing you depending on the specific situation.
Chris
On Mon, Nov 9, 2015 at 12:06 PM, Matt Adams <MAdams@xxxxxxxxxxxxxxxxxxx>
wrote:
I can understand not gathering histograms across all columns due to the
potential time it would take to do so. Is there any other technical reason
not to..(perhaps some issue with the optimizer I'm not currently aware of)?
I routinely gather histogram information for all INDEXED columns.
Matt Adams
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Wolfgang Breitling
Sent: Monday, November 09, 2015 12:13 PM
To: kp0773@xxxxxxxxx
Cc: Oracle-L@xxxxxxxxxxxxx
Subject: Re: gather stats
Use auto_sample_size and refrain from gathering histograms on all columns
( method_opt 'for all columns size 1')
Sent from my iPhone. Typing errors may have occurred.
On Nov 9, 2015, at 10:01, K R <kp0773@xxxxxxxxx> wrote:2.5 TB) . If i keep estimate percent 10,15 then some of the table are
All,
What is the recommended way of gathering stats on 11gR2 database (
taking hours and hours .
Please let me know .--
Thanks in advance.
Kart.
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