Re: V$active session history

You are right. By default, every 10th sample is written from in-memory ASH to AWR. We can also control it via _ash_disk_filter_ratio parameter.

I#NameTypeValueISDEFAULTISSESISSYS_MODISMODIFIEDISADJDesc 1_ash_disk_filter_ratioInteger10TRUEFALSEIMMEDIATEFALSEFALSERatio of the number of in-memory samples to the number of samples actually written to disk

Regards,
Vishal Gupta

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> Reply-To: <jonathan_at_jlcomp.demon.co.uk> Date: Friday, 20 March 2015 09:41
To: ORACLE-L <oracle-l_at_freelists.org> Subject: RE: V$active session history

>
> No,
> Ryan is correct.
>
> V$active_session_history takes a sample once every second.
> The content of a sample consists of every session that is active at the moment
> the sample was taken.
> The AWR (dba_hist_active_sess_history) reduces this to every 10th sample - i.e
> the result you would get if you sampled once every 10 seconds instead of once
> per second.
>
> You can confirm this, assuming that your ASH data survives for just a little
> more than the basic one hour target, by comparing the sample_time on the
> dba_hist_active_sess_history data of the most recent AWR snapshot with the
> sample_times from v$active_session_history for a similar period.
>
>
>
> Regards
> Jonathan Lewis
> http://jonathanlewis.wordpress.com
> _at_jloracle
>
> From: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] on behalf
> of Vishal Gupta [vishal_at_vishalgupta.com]
> Sent: 20 March 2015 09:25
> To: rjanuary_at_gmail.com
> Cc: jeremy.schneider_at_ardentperf.com; mohamed.houri_at_gmail.com; ORACLE-L
> Subject: Re: V$active session history
>
> Ryan,
>
> Session does have to be active for 10 secs to be included in AWR sample. AWR
> takes top 10% of the rows for every second and stored in repository.
>
> Regards,
> Vishal Gupta
>
> On 19 Mar 2015, at 18:11, Ryan January <rjanuary_at_gmail.com> wrote:
>
> I agree with Jeremy, but have a slight correction. As I understand it, every
> 10th ASH sample will make it to the dba_hist* views. A sql statement wouldn't
> have to be active a full 10 seconds to be included. That session can sit idle
> for 9.999 seconds and, by being active at just the right time, be included in
> the AWR sample.
>

>> On Mar 19, 2015, at 1:05 PM, Jeremy Schneider
>> <jeremy.schneider_at_ardentperf.com> wrote:
>> 
>> every SQL that runs for more than 1 second will show up in
>> v$active_session_history (until the memory buffer cycles around).
>> every SQL that runs for more than 10 seconds will be retained in the
>> dba_hist_* view.

--
http://www.freelists.org/webpage/oracle-l