kcbget

Maclean Liu(刘相兵

Question:

I have found your very interesting article:
https://profiles.google.com/113940305066161026918/buzz/Ku1Qyb1igBg

Could you please be so kind and share some places unclear for me.

1)
What do you know about difference between kcbget and kcbgcur?
kcbgcur is usually used for current get or db block get,
kcbget is also used for it, as I noticed.
Do these functions do similar work or absulutely different?

2)
You wrote:
kcbgtcr:

• If successful, returns the “best” candidate (performed by ktrexf or examination function)
• Scans the hash bucket for the DBA for buffers that may be used to build a CR buffer
• If not successful, calls kcbget

If not successful, calls kcbget for what?
3)
And maybe do you know how exactly SCN is passed into kcbgtcr ?
kcbgtcr should knows which for which SCN it should finds buffer, right? or not?

Maclean Liu(刘相兵

Answer:

1. these three function do different work.




2. why call kcbget ?  Actually my context is getting CR buffer in RAC environment ;

kcbget:
Retries the scan just tried by kcbgtcr

If you find a buffer, you return it now.
If not, then if it is being READ in or there is a current mode buffer, you wait until it is available and then rescan the buffer.
If these fail, you cannot use any locally cached buffers.

If the above fails:
CR server manages the CR request.

The CR server was a separate background process in Oracle8i. In Oracle9i and later, the same functionality is part of the LMS process