Hi Jonathan, Yes. tested in 11.2.0.2, 11.2.0.3 and found a similar behaviour as reported by you. Blocking TM locks not captured by v$WAIT_CHAINS Cross checked the documentation and it states V$WAIT_CHAINS is intended to capture all blocked sessions but ends up capturing only blocking TX locks and not blocking TM locks as tested. V$WAIT_CHAINS is built on top of X$KSDHNG_CHAIN and from what i understand , this view is populated by DIAG process every 3 seconds for local hang analyse information and every10 seconds for RAC. I would read the missing TM locks behaviour as a bug. Not sure how others would read this interestingly, one more observation I had and is new learning to me and could be useful to others Session 1. Lock table in exclusive mode Session 2. Update a row in the table Session 3. Update the same row that is locked in session 2 We will see session 2 and 3 waiting on Enqueue TM Contention. Now issue a commit or rollback on session 1. Session 3 would still show a TM contention. I was expecting a TX Enqueue when the first session completed but Oracle decides to keeps the old TM lock mode as the blocking mode. Thanks again got to learn 2 new items today best regards sriram kumar On Fri, Jan 18, 2013 at 2:00 PM, Jonathan Lewis <jonathan@xxxxxxxxxxxxxxxxxx > wrote: > > > I've just tried a simple test on an 11.2.0.3 instance. > Get 3 sessions to lock a table in exclusive mode - one gets it, the other > two queue. > The query returned no rows. In fact v$wait_chain held no rows. > > I haven't checked the documentation yet, but the waits captured by > v$wait_chain may include all the common waits we might like. > > > Regards > > Jonathan Lewis > http://jonathanlewis.wordpress.com/all-postings > > Author: Oracle Core (Apress 2011) > http://www.apress.com/9781430239543 > > ----- Original Message ----- > From: "John D Parker" <orclwzrd@xxxxxxxxx> > To: "Sriram Kumar" <k.sriramkumar@xxxxxxxxx> > Cc: "oracle-l" <oracle-l@xxxxxxxxxxxxx> > Sent: Wednesday, January 16, 2013 6:32 PM > Subject: Re: query for waiters queue > > > | It appears that you win the prize! > | > | ________________________________ > | From: Sriram Kumar <k.sriramkumar@xxxxxxxxx> > | To: orclwzrd@xxxxxxxxx > | Cc: oracle-l <oracle-l@xxxxxxxxxxxxx> > | Sent: Wednesday, January 9, 2013 7:51 PM > | Subject: Re: query for waiters queue > | > | > | Hi, > | > | you can look at the following script by Guy Harrison. Displays the chain > of locks > | > | http://guyh.textdriven.com/OPSGSamples/Ch15/wait_chains.sql > | > | best regards > | > | sriram kumar > | > | > | > | On Thu, Jan 10, 2013 at 12:27 AM, John D Parker <orclwzrd@xxxxxxxxx> > wrote: > | > | So I have all the classic queries for finding blockers and waiters. I > keep running into the situation where I have one holder and 600 waiters. I > clear off the blocker and then another one picks up and blocks. Is there a > query that will give the current waiter queue? I see that Jonathan talks > about a trace event to create a trace file but that's not particularly > useful in my situation. Anyone have a query for this? > | >Thanks in advance! > | > > | >John > | > > | >-- > | >//www.freelists.org/webpage/oracle-l > | > > > -- > //www.freelists.org/webpage/oracle-l > > > -- //www.freelists.org/webpage/oracle-l