Re: CR Block copies, always 6 in 10.2.0.3?

  • From: amonte <ax.mount@xxxxxxxxx>
  • To: "조동욱" <ukja.dion@xxxxxxxxx>
  • Date: Mon, 24 Mar 2008 12:52:20 +0100

Do you have the wait interface ebook?


Its in page 221 where it says:

"To avoid flooding the buffer cache with cloned buffers, Oracle limits the
number of cloned buffers (or cr copies) to six per data block address . Once
the limit is reached, *Oracle waits for the buffer; the normal wait time is
10cs before it attempts to clone/reread the buffer*"

TIA

Alex


On Mon, Mar 24, 2008 at 12:15 PM, 조동욱 <ukja.dion@xxxxxxxxx> wrote:

> I read from somewhere, I think the wait interface book where it states
> that the number of clone copies of data block is governed by
> _DB_BLOCK_MAX_CR_DBA which is set to 6. If there will be more than 6 copies
> then Oracle will wait for the buffer, this is what I dont get, wait?
>
> Can you point us to the original doc?
> I've never heard that consistent read is blocked and being waited by any
> reason.
> (One exception is that buffer lock contention which is caused by physical
> read - read by other session wait event)
>
> As you observed it right, cr blocks are recycled by age.
> The olest one is replaced by new cr block.
> You can verify it using x$bh view.
>
>
> Dion Cho
>
> PS)
> "I read somewhere..." kind of thing seems not to be a good habit.
> You'd better leave a link to original doc or make the replayable test case
> yourself.
>
>
>

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