CR Block copies, always 6 in 10.2.0.3?

  • From: amonte <ax.mount@xxxxxxxxx>
  • To: oracle-l <oracle-l@xxxxxxxxxxxxx>
  • Date: Mon, 24 Mar 2008 01:10:05 +0100

Hi all

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?

So I fired up 7 sessions and see what kind of wait is this! I updated the
same table (EMP from scott tiger), 14 rows in same data block and each
session updates a row, then each session fires a query agaisnt EMP. I
noticed that the number of CR is never more than 6 despite having 7 updates
concurrently and I dont see what is really going on. Does this mean whenever
the 7th CR block is being cloned one of 6 previous CR is being overwritten
or "destroyed"?

I did the test in 10.2.0.3.

TIA

Alex

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