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Home -> Community -> Mailing Lists -> Oracle-L -> 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.
> PQ slaves uses direct reads bypassing the SGA to read the segment blocks =
> which requires waiting to flush all committed
> changes in the SGA (dirty buffers) of that object to make sure the PQ =
> slaves
> will access the most recent version of that object.
>
> Regards,
>
> Waleed
>
> -----Original Message-----
> From: Diego Cutrone [mailto:diegocutrone_at_yahoo.com.ar]
> 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 =
> of TC enqueues
> I have read that TC enqueue stands for "Thread Checkpoint enqueue".=20
>
> Anybody knows what are they used for? what kind of resources they =
> 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=20
> PX Deq: Execute Reply=20
> PX Deq: Table Q Normal=20
> PX Deq: Parse Reply=20
>
> Does anybody know where I can get a description for them?=20
> 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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