Re: consistent read gets

----- Original Message -----

From: Bobak, Mark

To: Multiple recipients of list ORACLE-L

Sent: Monday, January 26, 2004 6:39 PM

Subject: RE: consistent read gets

(I'm sending the reply to the freelists.org list as well.  Hope you all agree that's a reasonable thing to do.)

 

no work - consistent read gets - Oracle needs a block that's consistent w/ a particular SCN, goes to the buffer cache, finds it there.  It's done.
cleanouts only - consistent read gets - Oracle needs a block that's consistent w/ a particular SCN, goes to the buffer cache, finds it there, but discovers it was recently modified and never cleaned out.  It needs to do extra work to clean out the block.
rollbacks only - consistent read gets - Oracle needs a block that's consistent w/ a particular SCN, goes to the buffer cache, finds it there, but discovers that the SCN on the block is too recent.  So, it refers to data stored in rollback, to roll back the block until it's old enough to be consistent w/ the query SCN.
cleanouts and rollbacks - consistent read gets - Oracle needs a block that's consistent w/ a particular SCN, but discovers it needs to cleanout the block, does so, then discovers it needs to roll it back, and does that too.

 

Hope that's clear.  In reality, there are lots of different types of situations that can occur.  The above is probably a bit simplified, but I think accurate as far as it goes.

 

-Mark

 

 

 

Mark J. Bobak
Oracle DBA
ProQuest Company
Ann Arbor, MI
"Imagination was given to man to compensate him for what he is not, and a sense of humor was provided to console him for what he is."  --Unknown

-----Original Message-----
From: Sultan Syed [mailto:ssyed@fine.ae]
Sent: Monday, January 26, 2004 8:44 AM
To: Multiple recipients of list ORACLE-L
Subject: consistent read gets

Hi all,

Could somebody give example scenario for the followings please

 

no work - consistent read gets                      
cleanouts only - consistent read gets               
rollbacks only - consistent read gets               
cleanouts and rollbacks - consistent read gets

 

 

And

Is ther difference between consistent read gets and consistent gets?

 

Thanks in advance

Syed

 

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Author: Sultan Syed
  INET: ssyed_at_fine.ae

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