So with the introduction of Adaptive plans and Adaptive Statistics in 12c where
Oracle can (in theory) optimize plans based on the feedback, would histograms
still pose issues? I mean, wouldn’t the optimizer be able to handle any bad
plans through its Adaptive features if it indeed makes a bad choice in the
beginning?
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Chris Taylor
Sent: Monday, November 09, 2015 1:14 PM
To: MAdams@xxxxxxxxxxxxxxxxxxx
Cc: oracle-l
Subject: Re: gather stats
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<mailto: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>
[mailto: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<mailto:kp0773@xxxxxxxxx>
Cc: Oracle-L@xxxxxxxxxxxxx<mailto: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<mailto:kp0773@xxxxxxxxx>>--
wrote:
All,
What is the recommended way of gathering stats on 11gR2 database ( 2.5 TB)
. If i keep estimate percent 10,15 then some of the table are taking hours
and hours .
Please let me know .
Thanks in advance.
Kart.
