RE: TC Enqueue waits
- From: "Khedr, Waleed" <Waleed.Khedr@xxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 30 Apr 2004 22:57:55 -0400
I can't say that I'm 100% sure about the details, but I can say I was =
able to observe this behavior many times in environments that mix oltp =
(serial transactions) and Data Warehouses (reports that use PQO).
Also think about the fact, that direct reads go directly to files/TS =
where there might be a chance of having some dirty buffers that belong =
to that segment & Tablespace that could really affect the =
uniqueness/integrity of data being extracted by direct reads.
I'm sure many of the enqueue/X$/v$ experts on this list can correct me =
or add more details.
Regards,
Waleed
-----Original Message-----
From: Diego Cutrone [mailto:diegocutrone@xxxxxxxxxxxx]
Sent: Friday, April 30, 2004 6:54 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: TC Enqueue waits
Thank you Waleed
Let me confirm what I understood.
So you're telling me that when an object needs to be accessed by using =
PQO,
the session that required this access will (possible) have to wait
on a TC enqueue waiting for the dirty buffers to get into disk. did I =
get it
correctly?
I thought the session used to waiting on the cross instance call (CI)
enqueue while an object checkpoint was taking place (before a direct =
read
takes place)....
Please, let me know your thoughts.
Thanks!
Diego.
----- Original Message -----=20
From: "Khedr, Waleed" <Waleed.Khedr@xxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, April 30, 2004 10:50 AM
Subject: RE: TC Enqueue waits
> PQ slaves uses direct reads bypassing the SGA to read the segment =
blocks =3D
> which requires waiting to flush all committed
> changes in the SGA (dirty buffers) of that object to make sure the PQ =
=3D
> slaves
> will access the most recent version of that object.
>
> Regards,
>
> Waleed
>
> -----Original Message-----
> From: Diego Cutrone [mailto:diegocutrone@xxxxxxxxxxxx]
> Sent: Friday, April 30, 2004 4:25 PM
> To: Oracle List
> Subject: TC Enqueue waits
>
>
> Hi List.
> I have detected high enqueue waits in one instance.
> After quering x$ksqst I realized most of them were TX and TC enqueues.
>
> I'm on the TX enqueues by tracing some sessions. But I have never =
heard =3D
> of TC enqueues
> I have read that TC enqueue stands for "Thread Checkpoint =
enqueue".=3D20
>
> Anybody knows what are they used for? what kind of resources they =3D
> protect?
>
> And I have another quick question:
>
> I'm also seeing Parallel query events like:
>
> PX Deq: Execution Msg
> PX Idle Wait
> PX qref latch=3D20
> PX Deq: Execute Reply=3D20
> PX Deq: Table Q Normal=3D20
> PX Deq: Parse Reply=3D20
>
> Does anybody know where I can get a description for them?=3D20
> I'd like to know which ones can be ignored and which ones can't.
>
> Thank you very much
> Regards
> Diego
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