RE: Blocking_session is blocker or blocked

From: Matt Adams <madams_at_equian.com>
Date: Thu, 8 Aug 2019 17:11:33 +0000
Message-ID: <DM6PR10MB41879B38F7ACE846EF42B2AFA5D70_at_DM6PR10MB4187.namprd10.prod.outlook.com>



Examining 11.2.0.4, V$SESSION has four columns related to blocking that can be useful for weeding out false positives.
(especially when processes are very briefly blocked by things like the DBWR and LGWR processes.
This is a very common problem on one of my systems that very frequently experiences blocking issues.)

COLUMN_NAME



BLOCKING_SESSION_STATUS
BLOCKING_SESSION
FINAL_BLOCKING_SESSION_STATUS
FINAL_BLOCKING_SESSION
(Those last two are helpful you have a cascading blocking).

The two *_STATUS columns can have values of UNKNOWN, NOT IN WAIT, NO HOLDER and VALID. (and maybe others, those are just the ones I remember)

Matt Adams
"Doing linear scans over an associative array is like trying to club someone to death with a loaded uzi."

  • Larry Wall

From: Powell, Mark <mark.powell2_at_dxc.com> Sent: Thursday, August 08, 2019 12:48 PM To: ecandrietta_at_gmail.com; ORACLE-L <oracle-l_at_freelists.org>; Matt Adams <madams_at_equian.com> Subject: Re: Blocking_session is blocker or blocked

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Ecandrietta, being that the OP's posted query uses V$SESSION and that 'VALID' is not one of the five valid values of the STATUS column what column value are you referring to?

Mark Powell
Database Administration
(313) 592-5148



From: oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org> <oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>> on behalf of Matt Adams <madams_at_equian.com<mailto:madams_at_equian.com>> Sent: Thursday, August 1, 2019 1:07:52 PM To: ecandrietta_at_gmail.com<mailto:ecandrietta_at_gmail.com> <ecandrietta_at_gmail.com<mailto:ecandrietta_at_gmail.com>>; ORACLE-L <oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org>> Subject: RE: Blocking_session is blocker or blocked

You may want to add the clause

and blocking_session_status = 'VALID'

I've seen cases where blocking_session is not null, but the blocking_session_status != 'VALID'. I believe that both checks are needed to avoid giving false positives.

From: oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org> <oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>> On Behalf Of Eriovaldo Andrietta Sent: Thursday, August 01, 2019 11:06 AM To: ORACLE-L <oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org>> Subject: Blocking_session is blocker or blocked

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Hello,

In the sql below , the blocking_session is the BLOCKED or BLOCKER session ?

Select blocking_session, blocking_instance,wait_class, sid, serial#, inst_id, seconds_in_wait, program, module, s.LOGON_TIME From gv$session s
where blocking_session is not NULL
order by blocking_session;

Regards

Eriovaldo

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Received on Thu Aug 08 2019 - 19:11:33 CEST

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